Idiopathic Parkinson Disease
Idiopathic Parkinson disease is a progressive neurodegenerative disorder caused by loss of dopaminergic neurons in the substantia nigra pars compacta, manifesting as resting tremor, rigidity, bradykinesia, and postural instability.
Idiopathic Parkinson Disease (iPD)
Idiopathic Parkinson disease (iPD) is a chronic, progressive neurodegenerative disorder characterised by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the pathological hallmark of intraneuronal Lewy bodies (α-synuclein aggregates) [1][2][3]. It is the most common cause of parkinsonism, accounting for approximately 80% of all cases [2].
The term "parkinsonism" is a clinical syndrome — it refers to any condition that produces the combination of bradykinesia plus at least one of resting tremor or rigidity [1][4]. iPD is one specific aetiology of parkinsonism, distinguished from secondary (symptomatic) causes and "Parkinson-plus" syndromes by its clinical course, response to dopaminergic therapy, and absence of atypical features.
"Parkinson's disease" ≠ "Parkinsonism." Parkinsonism is the umbrella syndrome; iPD is the most common cause. Always think about the differential when you see parkinsonism.
Breaking down the name:
- Idiopathic (Greek: idios = one's own, pathos = suffering) → cause unknown/multifactorial
- Parkinson → eponymous, after James Parkinson's 1817 "Essay on the Shaking Palsy"
| Parameter | Detail |
|---|---|
| Prevalence | ~160 per 100,000 (~1% of population > 65 years) [3] |
| Incidence | ~20 per 100,000 per year [3] |
| Sex ratio | M:F ≈ 3:2 (male predominance, possibly oestrogen-protective) [3] |
| Age of onset | Typically 40–70 years, peak in 6th decade [3] |
| Early-onset PD | ~10% before age 50; ~1% before age 30 (think genetic causes — Parkin, PINK1) [3][5] |
| Familial | 5–10% of cases have a clear familial component [3] |
Relevance to Hong Kong
- Hong Kong has a rapidly ageing population. With > 20% of the population projected to be > 65 by 2030, the burden of iPD will increase proportionally.
- Drug-induced parkinsonism is particularly important in Hong Kong because of high usage of metoclopramide (廣泛使用的止嘔藥) and traditional Chinese medicine (some may contain manganese or heavy metals).
- Genetic studies in Chinese/East Asian cohorts show that LRRK2 G2385R variant is a risk factor with higher frequency than in Caucasian populations.
3. Risk Factors
| Factor | Mechanism |
|---|---|
| Age | Strongest risk factor. Cumulative oxidative stress, mitochondrial dysfunction, and protein misfolding increase with age |
| Male sex | Oestrogen may be neuroprotective for dopaminergic neurons (antioxidant, anti-inflammatory effects) |
| Family history | 2× risk if first-degree relative affected [3] |
| Genetics | LRRK2, SNCA, Parkin, PINK1, GBA mutations (see Aetiology) |
| Factor | Mechanism |
|---|---|
| Pesticide/herbicide exposure (rotenone, paraquat) | Mitochondrial complex I inhibition → selective dopaminergic neurotoxicity |
| Rural living / well-water drinking | Surrogate for pesticide exposure |
| Head trauma | Chronic neuroinflammation (e.g. "punch-drunk syndrome" / pugilistic encephalopathy) |
| Manganese exposure | Occupational (welders, miners); accumulates in basal ganglia |
| MPTP | A synthetic opioid contaminant; metabolised to MPP+ which is a mitochondrial complex I inhibitor — classic neurotoxin model for PD [3] |
| Factor | Proposed Mechanism |
|---|---|
| Cigarette smoking | Nicotine may stimulate dopamine release and have anti-inflammatory effects (inverse association consistently shown epidemiologically) |
| Caffeine intake | Adenosine A2A receptor antagonism — modulates basal ganglia circuitry |
| Physical exercise | Neuroplasticity, ↑BDNF, ↓neuroinflammation |
| NSAIDs (ibuprofen) | Anti-inflammatory; COX-2 inhibition may reduce microglial activation |
High Yield
The inverse association of smoking and caffeine with PD is a classic exam question. Remember: these are epidemiological associations, NOT recommendations for prevention.
4. Anatomy and Physiology of the Basal Ganglia
Understanding iPD requires a solid grasp of basal ganglia motor circuitry. This is the "why" behind every motor symptom.
| Structure | Role |
|---|---|
| Striatum (caudate + putamen) | Main input station of the basal ganglia; receives cortical glutamatergic input |
| Globus pallidus externus (GPe) | Relay in the indirect pathway |
| Globus pallidus internus (GPi) | Main output nucleus (inhibitory, GABAergic) → thalamus |
| Subthalamic nucleus (STN) | Excitatory relay in the indirect pathway (glutamatergic) |
| Substantia nigra pars compacta (SNpc) | Source of dopaminergic neurons projecting to striatum (nigrostriatal pathway) |
| Substantia nigra pars reticulata (SNr) | Output nucleus (like GPi) |
| Thalamus (ventral anterior/ventrolateral nuclei) | Relays basal ganglia output to motor cortex |
Think of the basal ganglia as a "brake and accelerator" system for movement:
Direct pathway ("GO" pathway):
- Cortex → Striatum (D1 receptors) → GPi/SNr (inhibitory) → Thalamus (disinhibited) → Motor cortex → Movement
- Net effect: facilitates movement (releases the thalamic brake)
Indirect pathway ("STOP" pathway):
- Cortex → Striatum (D2 receptors) → GPe (inhibitory) → STN (disinhibited, excitatory) → GPi/SNr (more inhibition) → Thalamus (more inhibited) → Motor cortex → Less movement
- Net effect: suppresses movement (applies the thalamic brake harder)
Role of Dopamine from SNpc:
- Dopamine from SNpc modulates the balance:
- D1 receptors (direct pathway): dopamine excites → promotes movement
- D2 receptors (indirect pathway): dopamine inhibits → reduces suppression of movement
- Therefore, dopamine overall facilitates movement via both pathways
Degeneration of dopaminergic neurons in the SNpc leads to [1][2][3]:
- ↓ D1 stimulation → Direct pathway underactive → Less facilitation of movement
- ↓ D2 inhibition → Indirect pathway overactive → More suppression of movement
- Net result: Overactivity of the indirect pathway → excessive inhibition of the thalamus → reduced excitation of motor cortex → bradykinesia, rigidity [2]
"60–80% of dopaminergic neurons are lost before motor symptoms emerge" — this is why there is a long prodromal phase with non-motor symptoms [2].
| Pathway | From → To | Function | In iPD |
|---|---|---|---|
| Nigrostriatal | SNpc → Striatum | Motor control | Bradykinesia, rigidity, tremor |
| Mesolimbic | VTA → Nucleus accumbens | Reward, motivation | Apathy, anhedonia, depression |
| Mesocortical | VTA → Prefrontal cortex | Cognition, executive function | Cognitive impairment, dementia |
| Tuberoinfundibular | Hypothalamus → Pituitary | Inhibits prolactin | (Not primarily affected in iPD, but relevant for drug side effects) |
| Hypothalamic | Hypothalamus | Autonomic regulation | Autonomic dysfunction [3] |
Why Non-Motor Symptoms Occur Early
Non-motor symptoms (anosmia, constipation, REM sleep behaviour disorder, depression) appear years before motor symptoms because neurodegeneration in iPD follows a caudal-to-rostral (bottom-up) pattern as described by Braak staging: it starts in the dorsal motor nucleus of the vagus and olfactory bulb (stages 1–2), progresses to the substantia nigra (stages 3–4, when motor symptoms appear), and eventually reaches the cortex (stages 5–6, when dementia develops).
5. Aetiology
The vast majority of iPD cases are sporadic with no identifiable single cause [5]. The pathogenesis is considered multifactorial, involving:
- Genetic susceptibility (polygenic risk)
- Environmental triggers (pesticides, toxins)
- Aging-related cellular decline (mitochondrial dysfunction, oxidative stress, impaired protein clearance)
5–10% of PD cases are familial [3][5]. Key genes to know:
| Gene (Locus) | Inheritance | Key Features |
|---|---|---|
| SNCA / PARK1 (α-synuclein) | AD | Point mutations or multiplications. Clinical and pathologic features overlap with MSA and DLB [5]. α-synuclein is the main component of Lewy bodies |
| Parkin / PARK2 | AR | Most common cause of early-onset PD (< 50 years). Symmetrical presentation, slowly progressive, good levodopa response [5] |
| PINK1 / PARK6 | AR | Early onset (< 50 years), slowly progressive, excellent response to levodopa [5] |
| LRRK2 / PARK8 | AD | MOST common monogenic form of PD [5]. Accounts for significant proportion of familial AND a smaller proportion of sporadic PD. The G2385R variant is a risk factor in East Asian populations |
| GBA (glucocerebrosidase) | Risk factor | Heterozygous GBA mutations are the most common genetic risk factor for PD overall. Homozygous mutations cause Gaucher disease |
Exam Pearl - Genetics
LRRK2 = most common monogenic cause of PD (autosomal dominant). Parkin = most common cause of early-onset PD (autosomal recessive). GBA = most common genetic risk factor for PD (not monogenic, but confers ~5× risk). These are distinct concepts — don't confuse them.
The key pathological mechanisms converge on dopaminergic neuronal death in the SNpc:
-
α-Synuclein misfolding and aggregation
- α-Synuclein is a presynaptic protein normally involved in vesicle trafficking
- In iPD, it misfolds → oligomers → fibrils → Lewy bodies (dense eosinophilic intracytoplasmic inclusions)
- Misfolded α-synuclein is toxic to neurons and can spread in a prion-like fashion (cell-to-cell transmission), which explains the Braak staging pattern
-
Mitochondrial dysfunction
- Complex I deficiency in the electron transport chain → ↑ reactive oxygen species (ROS) → oxidative damage
- PINK1 and Parkin are involved in mitophagy (clearance of damaged mitochondria); mutations → accumulation of dysfunctional mitochondria
-
Ubiquitin-proteasome system (UPS) and autophagy-lysosomal pathway failure
- Parkin is an E3 ubiquitin ligase; loss of function → impaired protein degradation → protein aggregation
- GBA encodes glucocerebrosidase (a lysosomal enzyme); mutations → ↓ lysosomal function → ↓ α-synuclein clearance
-
Neuroinflammation
- Activated microglia release pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) → further neuronal damage
- Creates a self-perpetuating cycle of degeneration
-
Oxidative stress
- Dopamine metabolism itself generates ROS (via MAO-B and auto-oxidation)
- SNpc neurons are particularly vulnerable because they have high metabolic demand, high iron content (Fenton reaction), and relatively low antioxidant defences
6. Pathology
- Depigmentation of the substantia nigra (and locus coeruleus): normally dark due to neuromelanin pigment in dopaminergic neurons; loss of neurons → pale appearance on cross-section
- Lewy bodies: eosinophilic intraneuronal inclusion bodies in the basal ganglia (and later cerebral cortex) [2][3]
- Composed primarily of aggregated α-synuclein with ubiquitin
- Initially found in brainstem → spread rostrally (Braak staging)
- Lewy neurites: dystrophic neurites containing α-synuclein aggregates
- Neuronal loss and gliosis (astrocytic scarring) in the SNpc
| Stage | Site of Pathology | Clinical Correlate |
|---|---|---|
| 1 | Dorsal motor nucleus of vagus, olfactory bulb | Anosmia, constipation, REM sleep behaviour disorder |
| 2 | Locus coeruleus, raphe nuclei | Depression, sleep disturbance |
| 3 | Substantia nigra (SNpc) | Motor symptoms begin (this is when clinical diagnosis is typically made) |
| 4 | Mesocortex (amygdala, temporal cortex) | Emotional and cognitive changes |
| 5–6 | Neocortex (diffuse) | Dementia (PD dementia) |
Why Anosmia and Constipation Come First
Braak stages 1–2 involve the olfactory bulb and dorsal motor nucleus of the vagus nerve. The vagus nerve controls gut motility, so its degeneration → constipation. Olfactory bulb degeneration → hyposmia/anosmia. These non-motor symptoms can precede motor features by 10–20 years.
7. Classification
This is the framework to think about when you see any patient with parkinsonism:
Causes of Parkinsonism (must know!) [2][4]:
| Category | Examples |
|---|---|
| Idiopathic Parkinson's disease (80%) | Sporadic / Familial (e.g. LRRK2, SNCA) [2] |
| Parkinson-plus syndromes | MSA, PSP, CBD, DLB [2] |
| Vascular parkinsonism | Lacunar infarcts at basal ganglia (characterised by lower body involvement) [2] |
| Drug-induced | Dopamine antagonists (antipsychotics, antiemetics), valproate, methyldopa [2][4] |
| Metabolic disorders | Wilson's disease, Huntington's disease, anoxic brain damage post-cardiac arrest [2] |
| Toxins | CO, Mn, MPTP [2] |
| Infections | Post-encephalitis, neurosyphilis [2] |
| Structural brain lesions | Tumours of basal ganglia, normal pressure hydrocephalus, head trauma (pugilist encephalopathy) [2] |
Drug-induced parkinsonism from metoclopramide, antipsychotics, or antihistamines is particularly important to identify as it is reversible [4].
| Subtype | Features | Prognosis |
|---|---|---|
| Tremor-dominant | Prominent resting tremor, less bradykinesia/rigidity | Better prognosis, slower progression |
| Akinetic-rigid (postural instability and gait difficulty — PIGD) | Prominent bradykinesia, rigidity, gait disturbance; relatively little tremor | Worse prognosis, faster cognitive decline |
| Mixed | Features of both | Intermediate |
The Hoehn and Yahr staging system helps assess disease severity [4]:
| Stage | Description |
|---|---|
| 1 | Unilateral involvement only |
| 1.5 | Unilateral and axial involvement |
| 2 | Bilateral involvement without impairment of balance |
| 2.5 | Mild bilateral disease with recovery on pull test |
| 3 | Mild to moderate bilateral disease; some postural instability; physically independent |
| 4 | Severe disability; still able to walk or stand unassisted |
| 5 | Wheelchair-bound or bedridden unless aided; complete invalidism requiring constant nursing care |
Clinical Pearl
Postural instability appearing early (within the first 3 years) is a red flag for Parkinson-plus syndromes (especially PSP) rather than iPD. In iPD, postural instability is typically a late feature [2].
8. Clinical Features
The clinical features of iPD are divided into motor and non-motor symptoms. The key teaching point is that non-motor symptoms often precede motor symptoms by years to decades (Braak staging), and they are commonly under-recognised.
8.1 Non-Motor (Prodromal) Symptoms
These arise from early neurodegeneration in brainstem nuclei, olfactory bulb, and autonomic nervous system, before the SNpc is significantly affected.
| Symptom | Pathophysiological Basis |
|---|---|
| Anosmia / hyposmia | Lewy body pathology in the olfactory bulb (Braak stage 1). One of the earliest features — can precede motor symptoms by > 10 years. Present in ~90% of iPD patients [2] |
| Pain | Musculoskeletal (rigidity-related), neuropathic (central sensitisation from dopamine depletion), dystonic pain (especially early-morning foot dystonia) |
| Fatigue | Likely multifactorial: central dopamine depletion, sleep disruption, depression |
| Symptom | Pathophysiological Basis |
|---|---|
| Constipation | Lewy body pathology in the dorsal motor nucleus of vagus and enteric nervous system (Braak stage 1). ↓ parasympathetic drive → ↓ gut motility. Can precede motor symptoms by > 10 years |
| Urinary frequency / urgency | Detrusor hyperactivity from loss of inhibitory dopaminergic control on the pontine micturition centre |
| Postural (orthostatic) hypotension | Degeneration of sympathetic postganglionic neurons → ↓ noradrenaline release → failure to vasoconstrict on standing. Can also be exacerbated by dopaminergic medications |
| Erectile dysfunction | Autonomic neuropathy affecting sacral parasympathetic outflow |
| Excessive sweating (hyperhidrosis) | Hypothalamic dopamine depletion → dysregulated thermoregulation |
| Choking / dysphagia | Pharyngeal muscle bradykinesia and rigidity → impaired swallowing coordination (important cause of aspiration pneumonia) [2] |
| Sialorrhoea (drooling) | NOT due to increased saliva production; rather, due to reduced frequency of swallowing from oropharyngeal bradykinesia |
| Symptom | Pathophysiological Basis |
|---|---|
| Depression | Degeneration of serotonergic (raphe nuclei) and noradrenergic (locus coeruleus) systems in Braak stage 2. Also ↓ dopamine in mesolimbic pathway → anhedonia. Affects ~40% of iPD patients |
| Anxiety | Similar pathophysiology to depression; noradrenergic system degeneration |
| Auditory hallucinations (AH) | Rare in untreated iPD; more common as side effect of dopaminergic medications. May also reflect cortical Lewy body spread [2] |
| REM sleep behaviour disorder (RBD) | Loss of normal REM atonia due to degeneration of brainstem nuclei (sublaterodorsal nucleus / locus coeruleus) → patients "act out" their dreams (punching, kicking during sleep). A very strong prodromal marker — up to 80% of RBD patients will develop PD or DLB within 10–15 years |
| Excessive daytime sleepiness | Multifactorial: nocturnal sleep disruption, medication effects, degeneration of wake-promoting nuclei |
| Apathy | ↓ dopamine in mesolimbic/mesocortical pathways → ↓ motivation and reward processing |
| Symptom | Pathophysiological Basis |
|---|---|
| Subcortical dementia | Executive dysfunction, slowed processing speed, visuospatial impairment, but relatively preserved language and memory recall (unlike Alzheimer's which is cortical). Due to mesocortical dopamine depletion + cholinergic nucleus degeneration [2][3]. Affects up to 80% of patients after 20 years of disease |
Subcortical vs Cortical Dementia
Subcortical dementia (PD, PSP, Huntington's): slow thinking (bradyphrenia), executive dysfunction, personality changes, but relatively preserved recall if given cues. Cortical dementia (Alzheimer's): aphasia, agnosia, apraxia, prominent anterograde amnesia with poor recall even with cues. PD-associated dementia tends to develop later in the disease course (> 10 years). If dementia develops within 1 year of motor symptoms, consider Dementia with Lewy Bodies (DLB) instead (the "1-year rule").
8.2 Motor Symptoms — The Cardinal Features
The four cardinal features of parkinsonism can be remembered using the mnemonic TRAP [4]:
| Letter | Feature |
|---|---|
| T | Resting Tremor |
| R | Rigidity |
| A | Akinesia / Bradykinesia |
| P | Postural instability |
For MDS diagnostic criteria, the core requirement is: Bradykinesia + at least one of (rest tremor OR rigidity) [2].
Definition: Reduction in both speed AND amplitude of voluntary movements [2].
- This is the hallmark of parkinsonism and the only mandatory feature for diagnosis
- Pathophysiology: ↓ dopamine in striatum → overactive indirect pathway → excessive thalamic inhibition → ↓ cortical motor output → slow, small movements
- Correlates with the degree of dopaminergic neuron loss in the SNpc [2]
Clinical manifestations:
| Feature | Description | Why? |
|---|---|---|
| Distal movements affected first | E.g. finger tapping, heel tapping [2] | Fine motor control requires the most precise basal ganglia–cortical integration |
| Micrographia | Handwriting becomes progressively smaller | Decrementing amplitude of repetitive movements |
| Hypomimia (masked face) | Reduced facial expression, infrequent blinking [2] | Bradykinesia of facial muscles |
| Microphonia | Low-volume, monotonous, tremulous speech [2] | Bradykinesia of laryngeal and respiratory muscles |
| Difficulty with ADLs | Buttoning, shaving, cutting food | Fine motor bradykinesia |
| Decrementing movements | Finger tapping starts normally but becomes smaller and slower with repetition | Progressive "motor fatigue" from dopamine depletion |
Special tests for bradykinesia [2]:
- Touch thumbs with fingers (finger tapping)
- Open and close fingers (hand grips)
- Heel tapping
- Look for progressive decrement in speed AND amplitude
A 4–6 Hz resting tremor that is the presenting symptom in ~70% of iPD patients.
| Feature | Detail | Pathophysiology |
|---|---|---|
| Pill-rolling tremor | Thumb abduction–adduction, finger flexion–extension, wrist pronation–supination [2] | Rhythmic oscillation generated by thalamocortical circuits that are disinhibited due to basal ganglia dysfunction |
| UL > LL | Can affect lips, jaw, tongue, legs [2] | |
| Worse when supported and not engaged in activity | Resting tremor ↑ at rest, ↓ with action [2] | Voluntary movement engages the corticospinal tract directly, temporarily overriding basal ganglia dysfunction |
| Re-emergence | Manifests after a latency of ~5 seconds when hands are outstretched [2] | Distinguishes PD re-emergent tremor from essential tremor (no latency) |
| Asymmetric | Typically starts unilaterally and remains asymmetric throughout | Asymmetric SNpc degeneration |
| Worsened by stress, anxiety, contralateral motor tasks | "Stress test": ask patient to count backwards or perform serial 7s — tremor becomes more apparent | Mental effort withdraws cortical suppression of the tremor circuit |
Velocity-independent increase in muscle tone throughout the range of motion (cf. spasticity, which is velocity-dependent — faster stretch = more resistance).
| Type | Description | Mechanism |
|---|---|---|
| Lead-pipe rigidity | Tonic resistance throughout the entire range of motion [2] | Continuous co-contraction of agonist and antagonist muscles due to loss of reciprocal inhibition in the basal ganglia |
| Cogwheel rigidity | Tremor superimposed on tonic resistance → ratchety, step-wise resistance [2] | Lead-pipe rigidity + resting tremor = cogwheel effect |
- Best elicited by slow passive movement of a joint (wrist, elbow)
- Froment's manoeuvre (activation phenomenon): ask the patient to perform repetitive movements with the contralateral limb (e.g., open and close the other hand) — this "unmasks" subtle rigidity because it withdraws cortical compensation
The key distinction from spasticity (UMN lesion): spasticity is velocity-dependent, has a "clasp-knife" quality, and is associated with hyperreflexia, clonus, and Babinski sign. Rigidity is velocity-independent and not associated with UMN signs.
- A late feature of iPD — if present early (within first 3 years), think Parkinson-plus (especially PSP) [2]
- Least responsive to dopaminergic therapy [2] (because it likely involves non-dopaminergic pathways — cholinergic, noradrenergic)
- Pathophysiology: loss of postural reflexes due to degeneration of brainstem/basal ganglia postural control circuits
- Tested by the pull test: stand behind the patient, give a firm pull backwards on the shoulders
- Normal: recovers in 1–2 steps
- Abnormal: takes > 2 steps back (retropulsion) or would fall without catching
| Feature | Description | Pathophysiology |
|---|---|---|
| Parkinsonian gait | Stooped posture, reduced arm swing, hesitation in initiation, difficulty turning, shuffling gait, festination [2] | Bradykinesia + rigidity + postural instability → flexed, shuffling gait. Festination = involuntary acceleration with small steps and forward lean (centre of gravity shifts forward faster than feet can keep up) |
| Freezing of gait (FOG) | Sudden, transient inability to move the feet ("feet glued to the floor"), especially at doorways, turns, or when approaching a target | Likely due to disruption of the supplementary motor area and basal ganglia locomotor circuits. A major cause of falls |
| Striatal hand phenomenon | Flexed MCPJs, extended IPJs, adducted thumb [2] | Dystonia from dopamine imbalance in the striatum — resembles an ulnar claw but is due to basal ganglia rather than peripheral nerve pathology |
| Impaired upward gaze | [2] (cf. PSP which has impaired downward gaze) | Mild vertical gaze limitation can occur in iPD (and normal ageing), but prominent downward gaze palsy is the hallmark of PSP |
| Tip-of-tongue phenomenon | Difficulty with word retrieval [2] | Bradyphrenia (slowed cognitive processing) |
| Infrequent blinking | [2] | Bradykinesia of levator palpebrae and orbicularis oculi |
| Dystonia | Sustained muscle contraction causing abnormal postures, especially early-morning foot dystonia (before first dose of levodopa) | Related to dopamine fluctuations; more common in young-onset PD |
| Glabellar tap sign (Myerson's sign) | Persistent blinking in response to repeated tapping on the glabella (forehead) — normally habituates after a few taps | Failure of frontal lobe–mediated habituation (not specific to PD) |
This is an extremely high-yield comparison for exams [2]:
| Feature | PD Tremor | Essential Tremor |
|---|---|---|
| Age | > 50 years | Bimodal (teenage & 50s) |
| Family history | < 1% | ~50% (autosomal dominant) |
| Tremor type | Resting | Action / Postural |
| Symmetry | Asymmetrical | Symmetrical |
| Frequency | 4–6 Hz | 6–12 Hz |
| Progression | Yes | No |
| Body parts | Hands, leg, jaw, tongue, chin | Hands, head (titubation), voice |
| Latency | Re-emerge after 5 seconds | None |
| Alcohol | No effect | Reduces tremor |
| Writing | Micrographia | Large, irregular |
Exam Favourite
The re-emergent tremor after a latency of ~5 seconds when hands are held outstretched is a key distinguishing feature of PD from essential tremor. Essential tremor appears immediately on posture with no latency.
Special tests for PD [2]:
| Test | Purpose |
|---|---|
| Bradykinesia tests: finger tapping, hand grips, heel tapping | Assess speed and amplitude decrement |
| Gait assessment (must perform!) | Look for shuffling, reduced arm swing, festination, freezing, turning difficulty |
| Vertical gaze | Rule out PSP (impaired downward gaze) |
| Cerebellar signs | Rule out MSA (cerebellar subtype) |
| BP (lying and standing) | Rule out MSA (severe orthostatic hypotension) and assess autonomic dysfunction |
| Pull test | Propulsion and retropulsion — assess postural instability |
| MoCA | Screen for dementia |
| Writing | Micrographia |
| Drug history | Exclude drug-induced parkinsonism |
| Chest examination | Look for DBS (deep brain stimulation) device if already treated |
9. Key Concepts from Lecture Slides
Cardinal features of parkinsonism: TRAP — resting Tremor, Rigidity, Akinesia/bradykinesia, Postural instability
Hoehn and Yahr staging: Stage 1 (unilateral) → Stage 5 (wheelchair-bound/bedridden)
Causes: idiopathic PD, drug-induced (metoclopramide, antipsychotics, antihistamines), PSP, MSA, Wilson's disease, NPH, MPTP, CO poisoning
Drug-induced parkinsonism is particularly important to identify as it is reversible. Common culprits: metoclopramide, antipsychotics, antihistamines.
Huntington's disease: autosomal dominant, CAG trinucleotide repeats on chromosome 4p16.3, caudate and putamen atrophy, triad of chorea + psychiatric manifestations + progressive dementia.
PD is one of the most common neurological conditions in older adults. Consider medication review — many drugs can worsen or cause parkinsonism.
Dementia with Lewy Bodies (DLB) shares pathology with PD (Lewy bodies), but DLB has dementia within 1 year of motor symptoms (or before), visual hallucinations, fluctuating cognition, and REM sleep behaviour disorder.
The "1-year rule": If dementia precedes or appears within 1 year of parkinsonism → DLB. If parkinsonism precedes dementia by > 1 year → PD dementia (PDD). Same pathological spectrum, different clinical presentation.
High Yield Summary
Definition: iPD is a chronic progressive neurodegenerative disease caused by loss of dopaminergic neurons in the SNpc, with Lewy body pathology.
Epidemiology: Prevalence ~1% over 65; M > F; peak onset 6th decade; 5–10% familial.
Pathology: Degeneration of SNpc → ↓ striatal dopamine → overactive indirect pathway → ↓ thalamic excitation of motor cortex. Lewy bodies (α-synuclein) spread caudal-to-rostral (Braak staging).
Genetics: LRRK2 = most common monogenic (AD); Parkin = most common early-onset (AR); GBA = most common genetic risk factor.
Cardinal motor features (TRAP): Bradykinesia (mandatory) + rest tremor and/or rigidity. Postural instability is late.
Non-motor features precede motor by 10–20 years: Anosmia, constipation, RBD, depression, fatigue.
Key distinctions: PD tremor is resting (4–6 Hz), asymmetric, with re-emergence after 5-second latency. Essential tremor is action/postural (6–12 Hz), symmetric, no latency, improved by alcohol.
Red flags for NOT iPD: Symmetric onset, early falls, early dementia, prominent autonomic failure, cerebellar/pyramidal signs, poor levodopa response, downward gaze palsy.
Drug-induced parkinsonism is reversible — always check drug history!
Active Recall - Idiopathic Parkinson Disease (Clinical Features)
[1] Lecture slides: GC 091. Unsteady gait cerebellar lesions; movement disorders; Parkinsonism.pdf [2] Senior notes: Maksim Medicine Notes.pdf (Neurology – Parkinsonism, p.248–250) [3] Senior notes: Ryan Ho Neurology.pdf (Section 5.2.2 Parkinson's disease, p.120) [4] Senior notes: learning_points_output.txt (Neurology – Two Cases of Movement Disorders) [5] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (Section III. Etiology, p.1297–1299) [6] Lecture slides: GC 037. Common neurological problems in older people.pdf [7] Lecture slides: GC 169. My grandmother keeps forgetting things Geriatric psychiatry, Dementia.pdf [8] Lecture slides: GC 241. Reference (1) - Alzheimers Dementia - Revised criteria for diagnosis and staging of Alzheimer s disease.pdf
Differential Diagnosis of Parkinsonism
When a patient presents with parkinsonism (bradykinesia + rest tremor and/or rigidity), your job is NOT to jump straight to "iPD" — it is to systematically work through the differential. Around 20% of parkinsonism is NOT idiopathic PD [2], and several of those causes are reversible (drug-induced) or have very different prognoses and management (Parkinson-plus syndromes). Missing these has real consequences.
The approach is best structured as: "Is this really iPD, or is there something else going on?"
The differential for parkinsonism can be organised into a clean aetiological framework. Think of it as concentric rings:
Causes of Parkinsonism (must know!) [2][4]:
| Category | Examples | Key Distinguishing Feature(s) |
|---|---|---|
| Idiopathic Parkinson's disease (80%) | Sporadic / Familial (e.g. LRRK2, SNCA) | Asymmetric onset, good levodopa response, slow progression, resting tremor |
| Parkinson-plus syndromes | MSA, PSP, CBD, DLB | Additional neurological signs beyond TRAP, poor levodopa response (except partially in MSA-P/DLB) |
| Vascular parkinsonism | Lacunar infarcts at basal ganglia | Characterised by lower body involvement [2]; stepwise deterioration; more symmetrical |
| Drug-induced | Dopamine antagonists (antipsychotics, antiemetics), valproate, methyldopa | Bilateral symmetrical onset; temporal relationship to drug start; reversible |
| Metabolic disorders | Wilson's disease, Huntington's disease, anoxic brain damage post-cardiac arrest | Young onset (Wilson's), chorea (Huntington's), history of cardiac arrest (anoxic) |
| Toxins | CO, Mn, MPTP | Occupational/exposure history |
| Infections | Post-encephalitis, neurosyphilis | History of encephalitic illness, positive syphilis serology |
| Structural brain lesions | Tumours of basal ganglia, normal pressure hydrocephalus, head trauma (pugilist encephalopathy) | Imaging findings, triad of NPH, boxing history |
3. Detailed Differential Diagnosis — Condition by Condition
Drug-induced parkinsonism from metoclopramide, antipsychotics, or antihistamines is particularly important to identify as it is reversible [4][9].
Why does it happen? These drugs are dopamine D2 receptor antagonists — they block dopamine's action in the striatum, functionally mimicking the dopamine deficiency of iPD. The indirect pathway becomes overactive, just as in iPD, but there is no neuronal death.
| Drug Class | Common Culprits | Mechanism |
|---|---|---|
| Antipsychotics | Haloperidol, risperidone, chlorpromazine | D2 receptor blockade in nigrostriatal pathway |
| Antiemetics | Metoclopramide, domperidone (domperidone less so — doesn't cross BBB well) | D2 receptor blockade |
| Antihypertensives | Methyldopa | Depletes central dopamine (false neurotransmitter) |
| Anti-epileptics | Valproate | Mechanism unclear; possibly GABAergic effects on basal ganglia |
| Antihistamines | H1 blockers (e.g. promethazine) | Anticholinergic + weak D2 antagonism |
| Others | Lithium, calcium channel blockers (flunarizine, cinnarizine) | Various mechanisms |
How to distinguish from iPD:
| Feature | DIP | iPD |
|---|---|---|
| Onset | Temporal relationship with drug initiation (weeks to months) | Insidious |
| Symmetry | Bilateral and symmetrical | Asymmetrical |
| Tremor | Often postural/action (not classic pill-rolling rest tremor) | Resting, pill-rolling |
| Other features | May have tardive dyskinesia (oro-buccal-lingual dyskinesia) [3] | No tardive dyskinesia |
| Reversibility | Improves weeks–months after stopping offending drug | Progressive |
| DaTscan | Normal presynaptic dopamine terminals | Abnormal (reduced uptake) |
Must-Know Clinical Point
Always take a thorough drug history [2] in any patient presenting with parkinsonism. DIP is the most common reversible cause of parkinsonism. In Hong Kong, metoclopramide ("胃必治") is widely prescribed for nausea, and many elderly patients are on antipsychotics for BPSD in dementia. Missing DIP means the patient suffers unnecessarily from a treatable condition.
3.2 Parkinson-Plus Syndromes (Atypical Parkinsonism)
These are neurodegenerative diseases that share parkinsonism with iPD but have additional prominent neurological features not explained by iPD alone [5]. Key unifying features of Parkinson-plus syndromes:
- Presents with parkinsonism features BUT also with prominent degrees of pyramidal signs, cerebellar involvement and dysautonomia [5]
- Relatively symmetrical presentation (except CBD) [5]
- Poor or no response to levodopa [5]
- Faster progression than iPD
- Cognitive function is relatively well-preserved compared with PD probably reflecting a lower degree of cortical involvement [5] (except DLB which has prominent early dementia)
MSA = "multiple systems" are affected. Breakdown: three subtypes reflecting which system predominates.
MSA is pathologically characterised by aggregation of α-synuclein which affects oligodendroglia instead of neurons [5] (cf. iPD where Lewy bodies are in neurons). This is an α-synucleinopathy, like iPD and DLB, but the cell type affected is different.
| Subtype | Old Name | Key Features | Imaging |
|---|---|---|---|
| MSA-P (predominant parkinsonism) | Striatonigral degeneration | Symmetrical parkinsonism, poor levodopa response | Hyperintense lateral putaminal rim on T2 MRI [5] |
| MSA-C (predominant cerebellar ataxia) | Olivopontocerebellar atrophy | Cerebellar ataxia, scanning dysarthria, limb ataxia | Hot cross bun sign (hyperintense T2 signal in a cross pattern within the pons from degeneration of transverse pontocerebellar fibres) [5] |
| MSA-A (predominant autonomic failure) | Shy-Drager syndrome | Severe autonomic failure: postural hypotension, impotence, bladder dysfunction [5] | — |
Why to suspect MSA over iPD:
- Cerebellar signs (ataxia, nystagmus, dysmetria) → absolute exclusion criterion for iPD [2][5]
- Severe early autonomic failure (orthostatic hypotension with > 30 mmHg systolic drop within 3 minutes of standing, severe urinary retention) within 5 years of onset → red flag [5]
- Symmetrical parkinsonism
- Poor/absent levodopa response
- Inspiratory stridor (laryngeal dystonia from vagal nucleus degeneration) — very characteristic of MSA and is a red flag [5]
Rule out MSA: check for cerebellar signs and measure lying-standing BP [2].
PSP = "progressive" (worsening), "supranuclear" (the gaze palsy is above the level of cranial nerve nuclei — i.e. the nuclei themselves are intact but the descending cortical commands to them are disrupted), "palsy" (weakness/paralysis of gaze).
Pathology: Presence of protein tau in astrocytes, oligodendrocytes and neurons and neurofibrillary tangles (abnormal form of microtubule-associated protein tau) [5]. This is a tauopathy, NOT an α-synucleinopathy — fundamentally different from iPD/MSA/DLB at the molecular level.
Cardinal feature:
- Supranuclear vertical gaze palsy is the hallmark [5]
- Initially downward palsy followed by upward palsy [5]
- "Supranuclear" means voluntary saccades are impaired but reflexive eye movements (e.g. oculocephalic / doll's eye reflex) are preserved — because the brainstem nuclei themselves are intact
Other key features:
- Gait disturbance resulting in falls is a typical initial feature in the most classic phenotype [5]
- Falls tend to be backwards (retropulsion) — classic exam point
- Recurrent falls > 1/year within 3 years of onset is a red flag against iPD [5]
- Axial rigidity > limb rigidity (extended, upright posture — "rocket sign" — cf. iPD which is flexed/stooped)
- Early dysarthria and dysphagia
- Frontal lobe dementia (executive dysfunction, apathy, impulsivity)
Imaging: Hummingbird sign — prominent midbrain atrophy with relatively preserved pons resembling a hummingbird on midsagittal MRI [5]
Rule out PSP: always test vertical gaze, especially downward saccades [2]. Downward vertical supranuclear gaze palsy is an absolute exclusion criterion for iPD [5].
iPD vs PSP at a Glance
| Feature | iPD | PSP |
|---|---|---|
| Gaze | Impaired upward gaze (mild, also seen in ageing) | Impaired downward gaze (hallmark) |
| Posture | Flexed/stooped | Extended/upright ("rocket sign") |
| Falls | Late feature | Early feature (within first year), backwards |
| Tremor | Prominent resting tremor | Tremor usually mild or absent |
| Levodopa response | Good, dramatic | Poor |
| Pathology | Lewy bodies (α-synuclein) | Neurofibrillary tangles (tau) |
| Imaging | Usually normal early MRI | Hummingbird sign (midbrain atrophy) |
CBD = "cortico" (cortex) + "basal" (basal ganglia) — degeneration affects both cortical and subcortical structures.
Pathology: Intracellular aggregation of microtubule-associated protein tau [5] — another tauopathy, like PSP.
Key features:
- Progressive asymmetrical movement disorders with symptoms initially affecting one limb [5]
- Combinations of akinesia, rigidity, dystonia, focal myoclonus, ideomotor apraxia and alien limb phenomenon [5]
- Alien limb phenomenon: the affected limb moves involuntarily and the patient does not recognise it as their own — truly bizarre and pathognomonic for CBD
- Ideomotor apraxia: inability to perform learned motor tasks on command despite intact motor and sensory function
- Cognitive impairment is a common manifestation: executive dysfunction, aphasia, apraxia, behavioural change and visuospatial dysfunction [5]
- Cortical sensory loss (graphaesthesia, stereognosis with intact primary sensation) — this is an absolute exclusion criterion for iPD [5]
How to distinguish from iPD:
- CBD is the one Parkinson-plus that is also asymmetric — but it has cortical signs (apraxia, alien limb, cortical sensory loss) that iPD does not
- Myoclonus is prominent
- No meaningful levodopa response
DLB is really on the same pathological spectrum as iPD — both have Lewy bodies composed of α-synuclein. The distinction is clinical and somewhat arbitrary, based on the "1-year rule" [7][8].
"If dementia occurs before or within 1 year of motor symptoms of bradykinesia, rigidity, or resting tremor, a diagnosis of DLB can be established" [8]. If parkinsonism precedes dementia by > 1 year → PD dementia (PDD) [7].
Core clinical features of DLB (must have ≥ 2 for probable DLB) [7][8]:
| Feature | Prevalence | Detail |
|---|---|---|
| Cognitive fluctuations | 60–80% | Fluctuating attention and alertness; episodes of "blanking out", daytime drowsiness, bizarre behaviour interspersed with periods of near-normal function |
| Visual hallucinations | 67% | Occurs early; well-formed and detailed (people, children, animals) — unlike iPD where hallucinations are typically a late or drug-related phenomenon |
| REM sleep behaviour disorder | 85% | Dream enactment behaviour, vocalisation, complex motor behaviour; may precede other symptoms |
| Parkinsonism | 70–90% | Usually more bilaterally symmetric and milder than in PD |
- Severe sensitivity to antipsychotics (30–50%): acute irreversible parkinsonism, loss of consciousness ± neuroleptic malignant syndrome
- Repeated falls, syncope, autonomic dysfunction, hypersomnia, hyposmia
Dementia profile: Early impairments in attention, executive function, and visuoperceptual processing (memory affected late) [7] — contrasts with Alzheimer's disease where memory loss is the earliest and most prominent feature.
Imaging:
- MRI: Preserved medial temporal lobe structures (cf. AD which has hippocampal atrophy) [7]
- SPECT/PET: Generalised ↓ perfusion and ↓ metabolism, most marked in occipital areas [7]
- Dopamine transporter imaging (DaTscan) is most helpful in distinguishing DLB from Alzheimer disease [8]
Antipsychotic Sensitivity in DLB
This is a life-threatening complication. Patients with DLB given typical antipsychotics (and even some atypicals) can develop severe, irreversible parkinsonism, obtundation, or NMS. Only very low doses of atypical antipsychotics should be considered in DLB [7]. Quetiapine is generally safest; avoid haloperidol entirely.
Characterised by lower body involvement [2][3] — this makes intuitive sense because lacunar infarcts in the basal ganglia (from small vessel disease / lipohyalinosis) tend to affect the motor homunculus representation of the lower limbs preferentially in the putamen/caudate.
Key features:
- Lower limbs > upper limbs ("lower body parkinsonism")
- Stepwise deterioration (reflecting recurrent small vessel strokes) rather than smooth progression [3]
- More symmetrical than iPD [3]
- Poor response to levodopa [3]
- Associated with vascular risk factors (hypertension, diabetes, smoking, hyperlipidaemia)
- Gait: "magnetic gait" — feet stuck to the floor, wide-based, short steps (similar to NPH)
- Pseudobulbar affect and pyramidal signs may coexist (reflecting white matter ischaemia)
Imaging: Multiple lacunar infarcts in basal ganglia and/or subcortical white matter on MRI
Always consider in young patients (< 40–50 years) with parkinsonism, especially if there is liver disease.
Wilson's disease = autosomal recessive disorder of copper metabolism (ATP7B gene) → copper accumulates in the liver, brain (particularly basal ganglia — lenticular nuclei), and cornea.
Wilson's disease can mimic Parkinson's disease — extrapyramidal deposition of copper [10].
Key clues:
- Young age (typically < 40 years)
- Kayser-Fleischer rings (copper deposition in Descemet's membrane of the cornea — seen on slit lamp)
- Liver disease (hepatitis, cirrhosis, fulminant hepatic failure)
- Coombs-negative haemolytic anaemia [10] (copper directly damages red cell membranes)
- Movement disorder can include tremor, rigidity, dystonia, dysarthria ("wing-beating tremor" — a coarse postural/intention tremor is more characteristic than rest tremor)
- Psychiatric features (personality change, depression, psychosis)
Investigations: ↓ serum ceruloplasmin, ↑ 24-hour urinary copper, ↑ hepatic copper on biopsy, KF rings on slit lamp, genetic testing (ATP7B — though genetic test does not have to be positive to reach a diagnosis since the hereditary pathway is very heterogeneous [10])
The classic triad: "Wet, Wacky, Wobbly" — urinary incontinence, dementia, gait apraxia [3][7].
| Feature | Detail |
|---|---|
| Gait | Magnetic gait / gait apraxia — wide-based, shuffling, "feet glued to floor" (lower body parkinsonism) |
| Dementia | Frontal-subcortical type: mental slowing, apathy, inattention [7] |
| Urinary incontinence | Frontal lobe disinhibition of micturition reflex |
| Age | Commonest in 50–70 year age group [7] |
Why it mimics parkinsonism: The dilated ventricles compress the periventricular white matter and corona radiata fibres supplying the legs, producing a "lower body parkinsonism." There is NO true basal ganglia pathology.
Imaging: ALL ventricles enlarged disproportionate to sulcal effacement [7] (i.e. ventriculomegaly out of proportion to cortical atrophy — this distinguishes NPH from ex-vacuo hydrocephalus of Alzheimer's)
Key distinction from iPD:
- NPH: no resting tremor, gait apraxia (not festinating), urinary incontinence, no psychiatric symptoms, sleep disorder, or dysautonomic features [7]
- Treatable with VP shunt (CSF diversion) — therefore crucial not to miss
Autosomal dominant condition caused by CAG trinucleotide repeats on chromosome 4p16.3, leading to atrophy of the caudate and putamen [4].
Triad: chorea + psychiatric manifestations (depression, psychosis) + progressive dementia [4].
Why it enters the parkinsonism differential:
- The juvenile-onset (Westphal variant) of Huntington's disease can present with an akinetic-rigid phenotype rather than chorea — so it can look like parkinsonism [3]
- Juvenile-onset cases inherited from fathers tend to be more severe due to anticipation (expansion of CAG repeats during paternal meiosis) [4]
Key clues: Family history (AD), chorea, psychiatric features, caudate atrophy on MRI ("box-car" ventricles)
| Toxin | Source / Context | Mechanism |
|---|---|---|
| MPTP | Synthetic opioid contaminant (historically in illicit drug users) | Metabolised by MAO-B to MPP+, which is a mitochondrial complex I inhibitor → selective destruction of SNpc dopaminergic neurons [2][3] |
| Manganese (Mn) | Occupational: welders, miners, smelters | Accumulates in globus pallidus → "manganism." Typically affects GPi rather than SNpc, so less responsive to levodopa. Can cause dystonia + parkinsonism [2] |
| Carbon monoxide (CO) | House fires, faulty heating, deliberate self-harm | Causes bilateral globus pallidus necrosis (often delayed presentation weeks after exposure — "lucid interval") [2] |
| Rotenone | Pesticide | Mitochondrial complex I inhibitor (like MPTP) |
- Historically associated with encephalitis lethargica (von Economo's encephalitis, 1917–1928 pandemic) — now extremely rare [3]
- Any viral encephalitis affecting the basal ganglia can cause parkinsonism (e.g. Japanese encephalitis, HSV, HIV)
- May present years after the acute encephalitis
- Oculogyric crises (sustained upward gaze deviation) are a characteristic feature of post-encephalitic parkinsonism
Essential tremor is NOT parkinsonism — it is a pure tremor disorder without bradykinesia, rigidity, or postural instability. However, it is the most common movement disorder and the most frequent reason patients are referred "? PD."
The detailed comparison table was presented in the prior section [2], but the critical points for the differential are:
| Feature | iPD | Essential Tremor |
|---|---|---|
| Tremor type | Resting (4–6 Hz) | Action/Postural (6–12 Hz) |
| Symmetry | Asymmetric | Symmetric |
| Latency | Re-emergent after 5-second latency | No latency |
| Alcohol | No effect | Reduces tremor |
| Other signs | Bradykinesia, rigidity present | Isolated tremor only (no TRAP features) |
| Family history | < 1% | ~50% |
| Head tremor | No (jaw yes, head no) | Yes (titubation) |
4. Red Flags That Point AWAY from iPD
| Red Flag | Suggests Instead |
|---|---|
| Rapid progression of gait impairment requiring wheelchair within 5 years | PSP, MSA |
| Complete absence of motor progression ≥ 5 years | Not neurodegenerative — consider DIP, functional |
| Early bulbar dysfunction within 5 years (severe dysphonia, dysphagia) | MSA, PSP |
| Inspiratory respiratory dysfunction (stridor, frequent inspiratory sighs) | MSA (laryngeal dystonia) |
| Severe autonomic failure within 5 years (orthostatic hypotension, urinary retention) | MSA |
| Recurrent falls > 1/year within 3 years | PSP |
| Disproportionate dystonic contractures within 10 years | CBD |
| Absence of any common non-motor features despite 5 years of disease | Atypical — reconsider diagnosis |
| Pyramidal tract signs (weakness, hyperreflexia) | MSA, vascular parkinsonism |
| Bilateral symmetrical parkinsonism | DIP, vascular, MSA |
| Criterion | What It Points To |
|---|---|
| Unequivocal cerebellar abnormality (cerebellar gait, limb ataxia, sustained gaze-evoked nystagmus) | MSA-C |
| Downward vertical supranuclear gaze palsy | PSP |
| Probable behavioural variant FTD or primary progressive aphasia within 5 years | FTD spectrum |
| Parkinsonian features restricted to lower limbs ≥ 3 years | Vascular parkinsonism, NPH |
| Treatment with dopamine receptor blocker/depleter in dose and time consistent with DIP | DIP |
| Absence of observable response to high-dose levodopa despite moderate severity | Parkinson-plus, vascular |
| Unequivocal cortical sensory loss, clear limb ideomotor apraxia, or progressive aphasia | CBD |
| Normal functional neuroimaging of presynaptic dopaminergic system (DaTscan) | Not neurodegenerative parkinsonism (essential tremor, DIP, functional) |
| Diagnosis | Key Distinguishing Features | Pathology | Levodopa Response | Imaging |
|---|---|---|---|---|
| iPD | Asymmetric, resting tremor, good drug response, slow progression | Lewy bodies (α-synuclein) in SNpc | Excellent | Normal MRI early; ↓ DaTscan |
| MSA-P | Symmetric, autonomic failure, stridor | α-synuclein in oligodendroglia | Poor/transient | Putaminal rim sign |
| MSA-C | Cerebellar ataxia + parkinsonism | Same as MSA-P | Poor | Hot cross bun sign |
| PSP | Downward gaze palsy, early falls (backwards), upright posture | Tau (NFTs) | Poor | Hummingbird sign |
| CBD | Alien limb, apraxia, cortical sensory loss, asymmetric | Tau | Poor | Asymmetric cortical atrophy |
| DLB | Early dementia, visual hallucinations, RBD, cognitive fluctuations | Lewy bodies (cortical) | Partial | Preserved medial temporal lobe; occipital hypoperfusion |
| DIP | Bilateral, symmetric, temporal drug relationship, tardive dyskinesia | None (functional blockade) | N/A (stop drug) | Normal MRI; normal DaTscan |
| Vascular | Lower body, stepwise, vascular RFs, pyramidal signs | Lacunar infarcts | Poor | Multiple lacunes on MRI |
| Wilson's | Young, liver disease, KF rings, wing-beating tremor | Copper deposition | Poor | Basal ganglia hyperintensity |
| NPH | Wet-wacky-wobbly triad, wide-based gait, elderly | Ventricular dilation compressing periventricular WM | N/A (VP shunt) | Ventriculomegaly out of proportion to atrophy |
| Huntington's | FHx (AD), chorea, psychiatric, caudate atrophy | CAG repeats, caudate/putamen atrophy | N/A | Caudate atrophy, box-car ventricles |
When you see parkinsonism on the wards or in an exam, run through this mental checklist:
- Drug history → Stop any dopamine-blocking/depleting agents [2][4]
- Age → Young (< 40)? Think Wilson's, early-onset genetic PD (Parkin, PINK1)
- Symmetry → Bilateral symmetrical = red flag → DIP, MSA, vascular
- Eye movements → Downward gaze palsy = PSP [2][5]
- Cerebellar signs → Ataxia, nystagmus = MSA-C [2][5]
- Autonomic severity → Severe early orthostatic hypotension, urinary retention = MSA [2][5]
- Falls → Early falls (< 3 years) = PSP [5]
- Cognitive profile → Early dementia with visual hallucinations and fluctuations = DLB [7][8]
- Cortical signs → Apraxia, alien limb, cortical sensory loss = CBD [5]
- Gait pattern → Lower body predominant with vascular risk factors = vascular parkinsonism; magnetic gait with incontinence and dementia = NPH
- Liver disease → Wilson's [10]
- Family history → AD with chorea = Huntington's; AD parkinsonism = LRRK2; AR early-onset = Parkin/PINK1
- Levodopa trial response → Clear and dramatic response supports iPD [2]
High Yield Summary
Framework: 80% of parkinsonism = iPD. The remaining 20% = drug-induced, Parkinson-plus (MSA, PSP, CBD, DLB), vascular, metabolic (Wilson's), toxic (CO, Mn, MPTP), structural (NPH, tumours), infections (post-encephalitic), and inherited (Huntington's).
First step: Always check medication history — DIP is the most common reversible cause.
Red flags against iPD: Bilateral symmetric onset, early falls/bulbar symptoms/autonomic failure, downward gaze palsy, cerebellar signs, cortical sensory loss, pyramidal signs, poor levodopa response, rapid progression.
Absolute exclusions for iPD: Cerebellar abnormality, downward supranuclear gaze palsy, normal DaTscan, FTD within 5 years, lower limb restriction ≥ 3 years, cortical sensory loss/apraxia.
Key Parkinson-plus distinctions: MSA = cerebellar/autonomic + oligodendroglial α-synuclein; PSP = downward gaze palsy + early falls + tau; CBD = alien limb + apraxia + tau; DLB = early dementia + visual hallucinations + RBD + cortical Lewy bodies.
Essential tremor is NOT parkinsonism — action/postural tremor, no bradykinesia, no rigidity, symmetric, alcohol-responsive, high-frequency (6–12 Hz).
Active Recall - Differential Diagnosis of Parkinsonism
References
[2] Senior notes: Maksim Medicine Notes.pdf (Neurology – Parkinsonism, p.248–250) [3] Senior notes: Ryan Ho Neurology.pdf (Section 5.2.1–5.2.2, p.118–121, 134) [4] Senior notes: learning_points_output.txt (Neurology – Two Cases of Movement Disorders) [5] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (Differential diagnosis of PD, p.1298–1306) [7] Senior notes: Ryan Ho Psychiatry.pdf (Section 4.2.5 DLB, p.82–95) [8] Lecture slides: GC 241. Reference (3) - Patel dementia with lewy bodies.pdf (p.6–7) [9] Senior notes: Block A - I keep on bumping into people on my side_ pituitary tumours; hypopituitarism.pdf (Drugs causing hyperprolactinemia – dopamine antagonists) [10] Senior notes: Block A - Patients with non-viral chronic liver diseases.pdf (Wilson's disease section)
Diagnostic Criteria, Diagnostic Algorithm, and Investigations for Idiopathic Parkinson Disease
Before diving into criteria and investigations, understand this core concept:
Parkinson's disease is a clinical diagnosis [1][2]. There is no single blood test, imaging study, or biomarker that "confirms" iPD in routine practice. Investigations exist to support the clinical impression and — more importantly — to exclude mimics. The definitive diagnosis is neuropathological (Lewy bodies at autopsy), but clinically we rely on pattern recognition using validated criteria.
This is fundamentally different from, say, diagnosing an MI (where troponin and ECG are confirmatory). In iPD, you diagnose by:
- Recognising the motor syndrome (parkinsonism)
- Applying supportive criteria that increase confidence
- Checking for red flags and absolute exclusion criteria that point to alternative diagnoses
- Using investigations to rule out mimics, not to "prove" iPD
Neurological investigation is to confirm the clinical suspicion [11]. Caveat of pan-investigation: beware false positives (e.g. white matter changes, silent lacunar infarcts) and false negatives (e.g. "normal" nerve conduction, early disease where structural changes are not obvious) [11].
2. MDS Clinical Diagnostic Criteria for Parkinson Disease (2015)
The Movement Disorder Society (MDS) criteria are the current gold standard for clinical diagnosis. They establish two levels of diagnostic certainty: clinically established PD and clinically probable PD [2][5].
Presence of Parkinsonism: bradykinesia + rest tremor OR rigidity [2]
- Bradykinesia is mandatory — you cannot diagnose parkinsonism without it
- It must be combined with at least one of: resting tremor or rigidity
- Why bradykinesia is mandatory: it is the most specific feature of dopaminergic deficit in the nigrostriatal pathway. Tremor alone could be essential tremor; rigidity alone could be other causes. Bradykinesia with decrement is highly specific for basal ganglia dysfunction.
Step 2: Determine If Parkinsonism Is Due to iPD
Once parkinsonism is established, apply three filters:
≥ 2 supportive criteria are required for "clinically established" PD [2]:
| Supportive Criterion | Why It Supports iPD |
|---|---|
| Clear and dramatic beneficial response to dopaminergic therapy | iPD has intact postsynaptic D1/D2 receptors — when you supply exogenous dopamine (levodopa), the system responds. Parkinson-plus syndromes have postsynaptic receptor or downstream circuit damage, so they don't respond well |
| Levodopa-induced dyskinesia | Dyskinesias develop because of pulsatile dopamine receptor stimulation in a denervated striatum. This phenomenon is essentially unique to iPD — it proves that (a) there was significant presynaptic dopamine loss, and (b) the postsynaptic receptors are intact and hypersensitive |
| Rest tremor of a limb (documented on clinical examination) | Resting tremor is the most clinically specific motor feature for iPD among all causes of parkinsonism |
| Olfactory loss OR cardiac sympathetic denervation on MIBG scintigraphy | Anosmia reflects olfactory bulb Lewy body pathology (Braak stage 1); cardiac sympathetic denervation reflects postganglionic autonomic Lewy body pathology — both are relatively specific to Lewy body diseases (iPD/DLB) versus tauopathies (PSP/CBD) or MSA |
For "clinically probable" PD: only ≥ 1 supportive criterion is needed, but no red flags allowed and no absolute exclusion criteria present.
For "clinically established" PD: ≥ 2 supportive criteria are needed, AND no red flags, AND no absolute exclusion criteria.
No 'red flags' of atypical Parkinsonism [2][5]:
| Red Flag | What It Suggests |
|---|---|
| Bilateral symmetrical onset | DIP, vascular, MSA |
| Absence of motor progression over 5 years | Not neurodegenerative |
| Rapid deterioration of gait | PSP, MSA |
| Early bulbar / respiratory / ANS dysfunction / falls | MSA, PSP |
| Pyramidal signs (weakness, hyperreflexia) | MSA, vascular parkinsonism |
| Recurrent falls > 1/year within 3 years | PSP |
| Disproportionate dystonic contractures within 10 years | CBD |
| Absence of any common non-motor features despite 5 years | Reconsider diagnosis |
| Inspiratory respiratory dysfunction (stridor, inspiratory sighs) | MSA |
| Severe autonomic failure within 5 years | MSA |
Important exam nuance: A single red flag can be "counterbalanced" by supportive criteria in the MDS system, BUT if you accumulate multiple red flags, the diagnosis becomes much less secure. If red flags > supportive criteria, iPD is unlikely.
Absence of absolute exclusion criteria [2][5]:
| Exclusion Criterion | Diagnosis It Points To |
|---|---|
| Unequivocal cerebellar abnormalities | MSA-C |
| Downward vertical supranuclear gaze palsy | PSP |
| Probable behavioural variant FTD or PPA within 5 years | FTD spectrum |
| Parkinsonian features restricted to lower limbs ≥ 3 years | Vascular parkinsonism, NPH |
| Treatment with dopamine receptor blocker/depleter in dose and time consistent with DIP | DIP |
| Absence of observable response to high-dose levodopa despite at least moderate disease severity | Parkinson-plus |
| Unequivocal cortical sensory loss, clear limb ideomotor apraxia, or progressive aphasia | CBD |
| Normal functional neuroimaging of presynaptic dopaminergic system | Essential tremor, DIP, functional |
Clinically Established vs Clinically Probable iPD
| Clinically Established | Clinically Probable | |
|---|---|---|
| Parkinsonism | Yes (bradykinesia + tremor/rigidity) | Yes |
| Supportive criteria | ≥ 2 | ≥ 1 |
| Red flags | None | None |
| Absolute exclusions | None | None |
The distinction matters for research enrollment and prognostic certainty, but in clinical practice, "clinically probable PD" is sufficient to begin treatment.
4. Investigations
Investigations in iPD serve three purposes:
- Exclude structural and metabolic mimics (MRI, bloods)
- Support the diagnosis when clinical uncertainty exists (DaTscan, MIBG)
- Assess complications and comorbidities (cognitive testing, autonomic function tests)
These are "investigations" you can do at the bedside — and they are first-line.
| Assessment | What It Tests | Key Findings in iPD | Why |
|---|---|---|---|
| Finger tapping, hand grips, heel tapping [2] | Bradykinesia | Progressive decrement in speed AND amplitude | Direct assessment of nigrostriatal dopaminergic function |
| Gait assessment (must perform!) [2] | Overall motor function | Shuffling, reduced arm swing, festination, freezing, difficulty turning | Integrates bradykinesia, rigidity, and postural reflexes |
| Vertical gaze testing [2] | Rule out PSP (downward gaze palsy) | Normal or mildly impaired upward gaze in iPD | Downward supranuclear gaze palsy = absolute exclusion for iPD |
| Cerebellar signs [2] | Rule out MSA-C | Absent in iPD | Cerebellar abnormality = absolute exclusion for iPD |
| Lying and standing BP [2] | Rule out MSA, assess autonomic dysfunction | Mild orthostatic drop may occur in iPD; severe early OH (> 30 mmHg systolic within 3 min) suggests MSA | Sympathetic postganglionic degeneration |
| Pull test [2] | Postural instability (propulsion/retropulsion) | Abnormal in later stages of iPD; if abnormal early → red flag for PSP | Tests postural reflex integrity |
| MoCA [2] | Cognitive screening | May show executive dysfunction, visuospatial deficits (subcortical pattern) | Screens for PD-dementia vs DLB |
| Writing sample [2] | Micrographia | Progressively smaller handwriting | Decrementing amplitude — hallmark of bradykinesia |
| Drug history review [2] | Exclude drug-induced parkinsonism | Temporal relationship with dopamine-blocking drugs | Most important reversible cause |
| Chest wall inspection [2] | Look for DBS device | Pulse generator under skin (chest wall, subclavicular area) | If already treated with deep brain stimulation |
| Smell testing (e.g. UPSIT, Sniffin' Sticks) | Olfactory function | Hyposmia/anosmia in ~90% of iPD | Braak stage 1 pathology; supportive criterion in MDS criteria |
High Yield Exam Point - The Levodopa Challenge Test
A therapeutic trial of levodopa is itself an important diagnostic tool. A clear and dramatic beneficial response to dopaminergic therapy is one of the MDS supportive criteria [2]. In clinical practice, patients are started on levodopa, and if they show marked improvement (> 30% improvement in UPDRS motor score), this strongly supports iPD. Conversely, absence of observable response to high-dose levodopa despite at least moderate severity of disease is an absolute exclusion criterion for iPD [5] — this effectively means "if levodopa doesn't work, it's not iPD."
Routine blood tests do not diagnose iPD but are essential to exclude metabolic and secondary causes:
| Investigation | Purpose | What to Look For |
|---|---|---|
| CBC | Baseline; exclude anaemia from chronic disease | Normocytic anaemia may suggest chronic disease |
| LRFT (Liver and Renal Function Tests) | Baseline; screen for hepatic/renal causes | Deranged LFTs → consider Wilson's disease; renal failure can exacerbate drug toxicity |
| TFT (Thyroid Function Tests) | Hypothyroidism can cause slowness mimicking bradykinesia | ↑ TSH, ↓ fT4 → hypothyroidism |
| Calcium, Phosphate | Hypocalcaemia can cause movement disorders; hypercalcaemia causes lethargy | |
| Serum ceruloplasmin | Screen for Wilson's disease (especially if age < 50) | ↓ ceruloplasmin (< 0.2 g/L) suggests Wilson's |
| 24-hour urinary copper | Confirm Wilson's disease | ↑ urinary copper (> 100 μg/24h) |
| Serum copper | Wilson's | ↓ total serum copper (bound to ceruloplasmin); ↑ free copper |
| Peripheral blood film | Wilson's (haemolysis) | Coombs-negative haemolytic anaemia [10] |
| HIV serology | HIV encephalopathy can cause parkinsonism | If risk factors present |
| Syphilis serology (RPR/VDRL, TPHA) | Neurosyphilis | If clinical suspicion |
| Vitamin B12, folate | B12 deficiency can mimic neurological features |
When to Screen for Wilson's Disease
Always screen for Wilson's disease in any patient presenting with parkinsonism under the age of 50. Wilson's is treatable — if you miss it, the patient develops irreversible liver and brain damage. Minimum screening: serum ceruloplasmin + slit lamp examination for Kayser-Fleischer rings. The genetic test does not have to be positive to reach a diagnosis because the hereditary pathway of Wilson's is very heterogeneous — not just ATP7B [10].
4.3 Neuroimaging
| Aspect | Detail |
|---|---|
| Role | NOT used to diagnose iPD (MRI is typically normal in early iPD). Used primarily to exclude structural causes and support alternative diagnoses |
| When to order | All patients with parkinsonism should have at least one MRI brain to exclude mimics |
| Finding | Diagnosis Suggested |
|---|---|
| Normal | Compatible with iPD (especially early) |
| Multiple lacunar infarcts (basal ganglia, subcortical white matter) | Vascular parkinsonism |
| Hyperintense lateral putaminal rim (T2) | MSA-P [5] |
| Hot cross bun sign (pontine cross-shaped T2 hyperintensity) | MSA-C [5] |
| Hummingbird sign / Mickey Mouse sign (midsagittal midbrain atrophy) | PSP [5] |
| Asymmetric cortical atrophy (frontoparietal) | CBD |
| Ventriculomegaly out of proportion to sulcal atrophy | NPH [7] |
| Caudate atrophy ("box-car" ventricles) | Huntington's disease |
| Basal ganglia T2 hyperintensity (especially putamen/globus pallidus) | Wilson's disease, manganese toxicity |
| Bilateral globus pallidus necrosis | CO poisoning |
| Mass lesion (basal ganglia tumour, parasagittal meningioma) | Structural parkinsonism |
| Preserved medial temporal lobe structures | DLB (cf. AD which shows hippocampal atrophy) [7] |
This is the most important functional neuroimaging tool for the parkinsonism differential.
What it is:
- DaT = Dopamine Transporter
- Uses a radiotracer (e.g. ¹²³I-ioflupane / FP-CIT) that binds to the dopamine transporter (DAT) on presynaptic dopaminergic nerve terminals in the striatum
- SPECT imaging then visualises the density of these terminals
What it tells you:
- Normal DaTscan = intact presynaptic dopaminergic terminals → rules OUT neurodegenerative parkinsonism
- Abnormal DaTscan (reduced uptake) = loss of presynaptic dopaminergic terminals → consistent with neurodegenerative parkinsonism (iPD, MSA, PSP, CBD, DLB)
| DaTscan Result | Interpretation |
|---|---|
| Normal (symmetric comma-shaped uptake) | NOT neurodegenerative parkinsonism → consider essential tremor, DIP, dystonic tremor, functional/psychogenic tremor |
| Abnormal (asymmetric reduced uptake, "dot" or "comma-to-period" pattern) | Neurodegenerative loss of nigrostriatal dopaminergic terminals → compatible with iPD, MSA, PSP, CBD, DLB |
Normal functional neuroimaging of the presynaptic dopaminergic system is an absolute exclusion criterion for iPD [5]. This is the single most powerful investigation for ruling out iPD.
DaTscan Does NOT Distinguish iPD from Parkinson-Plus
A common misconception: DaTscan is NOT used to distinguish iPD from MSA/PSP/CBD — all of these show reduced presynaptic dopaminergic uptake. DaTscan is primarily used to distinguish neurodegenerative parkinsonism (iPD, Parkinson-plus) from non-degenerative tremor (essential tremor, DIP, functional).
What it is:
- MIBG = Meta-IodoBenzylGuanidine (a noradrenaline analogue)
- Taken up by postganglionic sympathetic nerve terminals, including those innervating the heart
- SPECT imaging visualises cardiac sympathetic innervation
Why it matters:
- In iPD and DLB, Lewy body pathology causes postganglionic sympathetic denervation → ↓ cardiac MIBG uptake (reduced heart-to-mediastinum ratio)
- In MSA, the autonomic failure is preganglionic → postganglionic neurons are intact → cardiac MIBG uptake is preserved/normal
- Cardiac sympathetic denervation on scintigraphy is an MDS supportive criterion for iPD [2]
| MIBG Result | Interpretation |
|---|---|
| Reduced cardiac uptake | Postganglionic denervation → supports iPD or DLB |
| Normal cardiac uptake | Intact postganglionic neurons → suggests MSA, PSP, or CBD rather than iPD |
This investigation is particularly useful when you need to distinguish iPD from MSA-P clinically (both can present with predominant parkinsonism). However, cardiac MIBG is not available for patients with DLB/PD in many countries [8] — in Hong Kong it is available at some centres.
| Type | Radiotracer | Use |
|---|---|---|
| ¹⁸F-DOPA PET | Fluorodopa | Measures presynaptic dopamine synthesis capacity. Shows reduced putaminal uptake in iPD. More sensitive than DaTscan but less available and more expensive |
| FDG-PET | ¹⁸F-fluorodeoxyglucose | Metabolic pattern analysis. Different patterns in iPD vs MSA vs PSP vs DLB. Research tool primarily |
Demonstrates perfusion to specific brain areas; different types of dementia typically present with different patterns of perfusion changes [12]:
| Pattern | Condition |
|---|---|
| Bilateral posterior temporal + parietal hypoperfusion | Alzheimer's disease [12] |
| Bilateral frontal + temporal hypoperfusion | Frontotemporal dementia [12] |
| Generalised ↓ perfusion, most marked in occipital areas | DLB [7] |
Dopamine transporter imaging is most helpful in distinguishing DLB from Alzheimer disease [8] — because both can present with cognitive decline, but only DLB has presynaptic dopaminergic loss visible on DaTscan.
| Test | Use in Parkinsonism |
|---|---|
| Polysomnography (PSG) | Confirms REM sleep without atonia in RBD. Polysomnographic confirmation of REM sleep without atonia is an indicative biomarker for DLB [8]; also supports iPD prodrome |
| Autonomic function tests | Tilt table test, Valsalva ratio, thermoregulatory sweat test → quantify autonomic dysfunction. Severe early autonomic failure suggests MSA over iPD |
| EEG | Not routinely used in iPD. Posterior slow-wave EEG activity with frequencies slower than 8 Hz is a supportive biomarker for DLB [8]. Also useful to exclude seizures or CJD (periodic sharp wave complexes) |
These are newer developments that are beginning to enter clinical practice:
| Biomarker | Principle | Status |
|---|---|---|
| α-Synuclein seed amplification assay (SAA) | Detects misfolded α-synuclein in CSF using amplification techniques. Sensitivity 59–95%, specificity 83–98% across Lewy body spectrum (DLB, PD, isolated RBD) [8] | Increasingly available; high sensitivity when neocortical Lewy body pathology present |
| α-Synuclein skin biopsy | Identifies phosphorylated α-synuclein in cutaneous nerve fibres. Sensitivity > 92% for synucleinopathies. Requires punch biopsies from three sites: posterior cervical, posterior thigh, posterior distal leg [8] | Under clinical validation |
| NfL (neurofilament light chain) in serum/CSF | Non-specific marker of neuronal damage. Higher in Parkinson-plus than iPD | Research/emerging clinical use |
The Future of PD Diagnosis
The 2023 NSD-ISS (Neuronal Synuclein Disease Integrated Staging System) proposes reclassifying PD biologically rather than clinically, using α-synuclein biomarkers (SAA) and dopaminergic deficit imaging (DaTscan) as "anchor" biomarkers. Under this system, you can have "biologically defined PD" even before motor symptoms appear. This is not yet in routine clinical use but represents where the field is heading.
| Differential to Exclude | Key Investigation | Expected Finding |
|---|---|---|
| Drug-induced parkinsonism | Drug history review; DaTscan if uncertain | Temporal drug relationship; normal DaTscan |
| Wilson's disease | Serum ceruloplasmin, 24h urine copper, slit lamp for KF rings | ↓ ceruloplasmin, ↑ urine copper, KF rings |
| NPH | MRI brain; CSF tap test (large-volume LP) | Ventriculomegaly; gait improvement after LP |
| Vascular parkinsonism | MRI brain | Multiple lacunar infarcts |
| MSA | MRI brain; cardiac MIBG; lying/standing BP | Hot cross bun / putaminal rim; normal MIBG; severe orthostatic hypotension |
| PSP | MRI brain; vertical gaze testing | Hummingbird sign; downward gaze palsy |
| CBD | MRI brain; clinical exam (apraxia, alien limb) | Asymmetric frontoparietal atrophy |
| DLB | Clinical criteria; DaTscan; SPECT/PET | Core features (fluctuations, VH, RBD, parkinsonism); ↓ DaT; occipital hypoperfusion |
| Huntington's | MRI brain; genetic testing (CAG repeats) | Caudate atrophy; ≥ 36 CAG repeats |
| Essential tremor | Clinical assessment; DaTscan if uncertain | Action/postural tremor only; normal DaTscan |
| Structural lesion | MRI brain with contrast | Mass, hydrocephalus |
Parkinson's disease: diagnosis — Clinical diagnosis. Presence of motor features: Bradykinesia + Rigidity + Resting tremor. Postural instability is typically a feature of more advanced disease [1].
Special tests for PD: Bradykinesia (touch thumbs with fingers, open and close fingers, heel tap); Gait (must perform!); Rule out Parkinson-plus: Vertical gaze (PSP), Cerebellar signs (MSA). To complete: BP (MSA), Pull test, MoCA (dementia), Writing (micrographia), Drug history, Chest (DBS) [2].
Neurological investigation is to confirm the clinical suspicion. Caveat of pan-investigation — false positive (white matter change / silent lacunar infarct) or false negative (early disease where structural changes are not obvious) [11].
High Yield Summary
iPD is a clinical diagnosis using MDS criteria: Bradykinesia (mandatory) + rest tremor or rigidity → then apply supportive criteria, red flags, and absolute exclusion criteria.
Clinically established iPD = ≥ 2 supportive criteria + no red flags + no exclusion criteria.
Supportive criteria: Dramatic levodopa response, levodopa-induced dyskinesia, rest tremor, anosmia/cardiac MIBG denervation.
Absolute exclusion criteria: Cerebellar signs, downward gaze palsy, cortical sensory loss/apraxia, normal DaTscan, no levodopa response, FTD within 5 years, lower-limb-only PD ≥ 3 years, DIP.
Investigation hierarchy:
- Bedside: gait, vertical gaze, cerebellar signs, BP, pull test, MoCA, drug history
- Bloods: CBC, LRFT, TFT, ceruloplasmin (if < 50), B12
- MRI brain: exclude structural causes; specific signs (hummingbird = PSP, hot cross bun = MSA-C, putaminal rim = MSA-P)
- DaTscan: distinguishes neurodegenerative (abnormal) from non-degenerative (normal) parkinsonism; does NOT distinguish iPD from Parkinson-plus
- Cardiac MIBG: distinguishes iPD/DLB (reduced) from MSA (normal)
- Levodopa trial: dramatic response = strong supportive criterion
Emerging: α-synuclein SAA in CSF (high sensitivity/specificity for synucleinopathies); α-synuclein skin biopsy (> 92% sensitivity).
Active Recall - Diagnostic Criteria and Investigations for iPD
References
[1] Lecture slides: GC 091. Unsteady gait cerebellar lesions; movement disorders; Parkinsonism.pdf [2] Senior notes: Maksim Medicine Notes.pdf (Neurology – Parkinsonism, p.248–250) [3] Senior notes: Ryan Ho Neurology.pdf (Section 5.2.1–5.2.2, p.118–121) [5] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (MDS criteria, red flags, exclusion criteria, p.1298–1306) [7] Senior notes: Ryan Ho Psychiatry.pdf (Section 4.2.5 DLB, p.82–95) [8] Lecture slides: GC 241. Reference (3) - Patel dementia with lewy bodies.pdf (p.6–7) [10] Senior notes: Block A - Patients with non-viral chronic liver diseases.pdf (Wilson's disease section) [11] Lecture slides: GCBA_Fundamentals_Neuro_Introduction to Neurological Investigations and Emergencies_Prof KC Teo.pdf (p.9) [12] Senior notes: Ryan Ho Diagnostic Radiology.pdf (Cerebral perfusion study, p.69)
Management of Idiopathic Parkinson Disease
Before jumping into drugs, understand the overarching philosophy:
- There is currently no disease-modifying (neuroprotective) therapy for iPD — all treatment is symptomatic. We are replacing or mimicking lost dopamine to improve motor function, but the underlying neurodegeneration continues.
- Treatment is individualised — the choice of first-line agent depends on the patient's age, dominant symptoms, functional impairment, comorbidities, and tolerance of side effects.
- Start treatment when symptoms cause functional impairment — there is no proven benefit to delaying or initiating treatment early purely for "neuroprotection." The decision to start is based on the patient's quality of life.
- Multidisciplinary approach is essential — physiotherapy, occupational therapy, speech and language therapy, and psychosocial support are as important as pharmacotherapy.
- Long-term motor complications (motor fluctuations and dyskinesias) from levodopa are inevitable in most patients and drive many management decisions.
3. Pharmacological Treatment — Detailed Drug Classes
The gold standard and most effective drug for motor symptoms of iPD.
Pharmacology — explained from first principles:
- Levodopa (L-DOPA) = L-3,4-dihydroxyphenylalanine, the natural biosynthetic precursor of dopamine
- Dopamine itself cannot cross the blood-brain barrier (BBB), but levodopa can (it is an amino acid transported by the large neutral amino acid transporter)
- Once levodopa crosses the BBB → it is converted to dopamine by aromatic L-amino acid decarboxylase (AADC) (also called DOPA decarboxylase) in the remaining nigrostriatal terminals and other brain cells
- Problem: AADC also exists peripherally (gut, liver, blood vessels). If you give levodopa alone, ~95% is decarboxylated peripherally → dopamine in the periphery causes nausea, vomiting, orthostatic hypotension, and cardiac arrhythmias, and very little reaches the brain
- Solution: Always co-administer with a peripheral decarboxylase inhibitor (DDI) that does NOT cross the BBB → blocks peripheral conversion → more levodopa reaches the brain, fewer peripheral side effects
| Combination | Brand Name | Components |
|---|---|---|
| Levodopa + benserazide | Madopar | Benserazide is the DDI |
| Levodopa + carbidopa | Sinemet | Carbidopa is the DDI |
The choice between Madopar and Sinemet is largely institutional preference. In Hong Kong, Madopar is more commonly used.
Why levodopa is the gold standard:
- Most potent symptomatic relief of motor symptoms
- Clear and dramatic beneficial response to dopaminergic therapy is itself an MDS supportive criterion for diagnosing iPD [2]
- All patients with iPD will eventually need levodopa
Side effects:
| Side Effect | Mechanism | Management |
|---|---|---|
| Nausea/vomiting | Dopamine stimulation of chemoreceptor trigger zone (area postrema — outside BBB) | Take with food; add domperidone (peripheral D2 antagonist — does not cross BBB, so does NOT worsen parkinsonism, unlike metoclopramide which DOES cross BBB) |
| Orthostatic hypotension | Peripheral dopaminergic vasodilation + central autonomic dysfunction | Slow dose titration; compression stockings; midodrine; fludrocortisone |
| Somnolence/sleep attacks | Central dopaminergic effects | Warn about driving |
| Impulse control disorders | Mesolimbic dopamine stimulation (less common with levodopa than with DA agonists) | Monitor; reduce dose |
| Hallucinations/psychosis | Cortical and limbic dopaminergic stimulation (particularly in advanced disease with cortical Lewy body spread) | See PD psychosis management below |
Long-term motor complications (these are the major management challenges — discussed in detail in Section 4):
- Wearing-off (end-of-dose deterioration)
- On-off fluctuations
- Levodopa-induced dyskinesia (peak-dose, diphasic, or off-state dystonia)
Levodopa and the Timing Dilemma
There was historical debate about whether to delay levodopa initiation to prevent motor complications ("levodopa-sparing" strategy). Current evidence (including the PD-MED and LEAP trials) suggests that delaying levodopa does NOT alter the natural course of motor complications — they are more related to disease duration and severity of dopaminergic denervation than cumulative levodopa exposure. However, in younger patients (< 65–70), dopamine agonists or MAO-B inhibitors are often tried first because younger patients have a higher lifetime risk of developing dyskinesias and a longer disease course ahead.
Exam Pitfall: Carbidopa/Levodopa and Falls
In the AOS Geriatrics case, Mrs. Wong (84F) on carbidopa/levodopa presents with a fall from dizziness upon standing — the answer is carbidopa/levodopa (D) as the most likely medication causing her fall [13]. Levodopa causes orthostatic hypotension via peripheral dopaminergic vasodilation and worsening of autonomic dysfunction. Always think of medication-related falls in the elderly.
These are synthetic drugs that directly stimulate dopamine receptors in the striatum, bypassing the need for presynaptic dopaminergic neurons.
Why use them?
- They have a longer half-life than levodopa → more stable dopaminergic stimulation → theoretically less pulsatile receptor stimulation → lower risk of motor fluctuations and dyskinesias than levodopa (this is the rationale for using them first in younger patients)
- Can be used as monotherapy in early disease or as adjunct to levodopa in advanced disease
| Drug | Type | Key Points |
|---|---|---|
| Pramipexole | Non-ergot, D2/D3 agonist | Often first-line DA agonist; also has antidepressant effects (D3 receptor in mesolimbic pathway). Renally excreted — reduce dose in CKD |
| Ropinirole | Non-ergot, D2/D3 agonist | Hepatically metabolised. Similar efficacy to pramipexole |
| Rotigotine | Non-ergot, D1/D2/D3 agonist | Transdermal patch — useful for patients with swallowing difficulty or erratic GI absorption. Provides continuous dopaminergic stimulation |
| Apomorphine | Non-ergot, D1/D2 agonist | Subcutaneous injection (rescue for "off" episodes) or continuous subcutaneous infusion (advanced therapy). Most potent DA agonist. Despite its name, it is NOT an opioid — "apo" = derived from morphine chemically, but acts on dopamine receptors |
| Bromocriptine, cabergoline, pergolide | Ergot-derived | Largely avoided now due to risk of fibrotic complications (retroperitoneal fibrosis, cardiac valvulopathy, pulmonary fibrosis) from 5-HT2B receptor agonism. Cabergoline still used in prolactinomas, less so in PD |
Side effects (class effects):
| Side Effect | Mechanism |
|---|---|
| Nausea/vomiting | Stimulation of CTZ (same as levodopa) |
| Orthostatic hypotension | Peripheral D2 vasodilation |
| Impulse control disorders (ICDs) | Stimulation of D3 receptors in the mesolimbic "reward" pathway → pathological gambling, hypersexuality, compulsive shopping, binge eating. More common with DA agonists than levodopa. Must counsel patients and families |
| Excessive daytime sleepiness / sleep attacks | Central D2/D3 effects |
| Hallucinations | Mesolimbic/cortical D2 stimulation |
| Peripheral oedema | Mechanism unclear; possibly D2-mediated renal effects |
| Dopamine agonist withdrawal syndrome (DAWS) | Abrupt cessation → anxiety, panic, dysphoria, pain, drug craving |
| Fibrotic reactions (ergot-derived only) | 5-HT2B receptor agonism on fibroblasts |
Impulse Control Disorders — Must Counsel
ICDs affect up to 15–20% of patients on DA agonists. They can be devastating (bankruptcy from gambling, relationship breakdown from hypersexuality). Always warn patients and families before starting DA agonists, and actively screen at every follow-up visit.
MAO-B = Monoamine Oxidase type B. This enzyme is the major metabolic pathway for dopamine in the brain. Inhibiting MAO-B → ↓ dopamine breakdown → ↑ dopamine availability in the synaptic cleft.
| Drug | Key Points |
|---|---|
| Selegiline (deprenyl) | Irreversible, selective MAO-B inhibitor. Metabolised to amphetamine/methamphetamine derivatives → may cause insomnia. Avoid evening dosing |
| Rasagiline | Irreversible, selective MAO-B inhibitor. No amphetamine metabolites → better tolerated than selegiline |
| Safinamide | Reversible MAO-B inhibitor + sodium channel blocker + glutamate release inhibitor. Dual mechanism |
Indications:
- Early monotherapy: Mild symptom relief; suitable as first agent in young patients with mild symptoms
- Adjunct to levodopa: Reduces "off" time by extending dopamine action; smooths out motor fluctuations
Side effects: Nausea, headache, insomnia (selegiline), orthostatic hypotension
Important drug interaction:
- MAO-B inhibitors + pethidine (meperidine) → serotonin syndrome (excitation, hyperthermia, rigidity, death). Avoid this combination absolutely.
- MAO-B inhibitors + SSRIs/SNRIs → theoretical serotonin syndrome risk (though rare at selective MAO-B doses). Use with caution, monitor.
COMT = Catechol-O-Methyltransferase. This enzyme methylates levodopa peripherally (to 3-O-methyldopa) and centrally (dopamine to 3-methoxytyramine). Inhibiting COMT → more levodopa available for brain delivery → prolongs levodopa's action.
| Drug | Acts Where | Key Points |
|---|---|---|
| Entacapone | Peripheral only | Always given WITH each levodopa dose (has no effect alone). Combination pill: levodopa + carbidopa + entacapone = Stalevo |
| Tolcapone | Peripheral + central | More effective but requires liver function monitoring (rare fatal hepatotoxicity) |
| Opicapone | Peripheral only | Once-daily dosing (long half-life); no hepatotoxicity concern; newest agent |
Indication: Adjunct to levodopa in patients with wearing-off motor fluctuations — by inhibiting peripheral COMT, you increase the bioavailability and half-life of levodopa, extending its "on" time
Side effects:
- Dyskinesias (because you are effectively increasing levodopa exposure — may need to reduce levodopa dose when adding a COMT inhibitor)
- Diarrhoea (especially entacapone)
- Orange discolouration of urine (entacapone) — harmless but warn patients
- Hepatotoxicity (tolcapone — monitor LFTs)
Rationale from first principles: In the normal striatum, there is a balance between dopaminergic (inhibitory) and cholinergic (excitatory) interneuron activity. When dopamine is depleted, the cholinergic system is relatively overactive → this contributes especially to tremor. Anticholinergics restore the balance by reducing cholinergic excess.
| Drug | Key Points |
|---|---|
| Trihexyphenidyl (benzhexol) | Most commonly used |
| Benztropine | |
| Procyclidine |
Indications:
- Tremor-dominant iPD, especially in younger patients — anticholinergics are most effective for tremor, less so for bradykinesia/rigidity
- Drug-induced parkinsonism (acute dystonic reactions from antipsychotics)
Contraindications / Caution:
- Elderly patients (> 65): avoid due to cognitive side effects — anticholinergics worsen memory and can precipitate delirium/dementia
- Closed-angle glaucoma (mydriasis → ↑ IOP)
- Prostatic hypertrophy (urinary retention)
- Cognitive impairment/dementia
Side effects (predictable from anticholinergic mechanism):
- Dry mouth, blurred vision, constipation, urinary retention, cognitive impairment, confusion, hallucinations
Mnemonic for anticholinergic side effects: "Blind as a bat, dry as a bone, red as a beet, mad as a hatter, hot as a hare, full as a flask" — mydriasis, dry mouth/skin, flushing, delirium, hyperthermia, urinary retention.
Mechanism: Multiple mechanisms — NMDA receptor antagonist (reduces glutamatergic excitotoxicity in the indirect pathway), enhances dopamine release, blocks dopamine reuptake, and has mild anticholinergic properties.
Key indications:
- Levodopa-induced dyskinesia — amantadine is the only oral medication with proven efficacy for reducing peak-dose dyskinesias (via NMDA antagonism — reduces excessive glutamatergic signalling from the overactive STN)
- Can provide mild symptomatic benefit in early PD (modest anti-parkinsonian effect)
Side effects:
- Livedo reticularis (mottled purplish skin discolouration, typically on legs)
- Ankle oedema
- Insomnia, hallucinations, confusion (especially in elderly)
- Renally excreted — reduce dose in CKD
4. Managing Motor Complications of Levodopa Therapy
After 5–10 years of levodopa therapy, ~50–80% of patients develop motor complications. These are the main reason for treatment adjustments and advanced therapies.
The pathophysiology relates to the interplay between progressive nigrostriatal denervation and pulsatile dopamine receptor stimulation:
- Early disease: Enough dopaminergic neurons survive to "buffer" exogenous levodopa — they take up levodopa, convert it to dopamine, store it, and release it steadily. This provides a smooth, sustained therapeutic effect.
- Advanced disease: Most dopaminergic terminals are lost → levodopa is now converted to dopamine by non-dopaminergic cells (serotonergic neurons, glia) that lack storage capacity → dopamine levels in the striatum mirror plasma levodopa levels → pulsatile stimulation of postsynaptic dopamine receptors → receptors undergo plastic changes (sensitisation) → dyskinesias and fluctuations.
| Complication | Description | Mechanism |
|---|---|---|
| Wearing-off (end-of-dose deterioration) | Motor symptoms return before the next levodopa dose is due. The "on" period gets progressively shorter | Shortened duration of levodopa benefit due to loss of dopaminergic neuronal buffering capacity; plasma half-life of levodopa (~90 min) becomes the limiting factor |
| On-off fluctuations | Unpredictable, sudden switches between "on" (mobile) and "off" (immobile) states, unrelated to dosing schedule | Unpredictable absorption and delivery of levodopa + severely reduced striatal buffering capacity |
| Peak-dose dyskinesia | Involuntary choreiform movements occurring at the time of peak plasma levodopa levels | Sensitised, denervated postsynaptic D1 receptors; excessive pulsatile stimulation |
| Diphasic dyskinesia | Dyskinesias occurring at the beginning and end of each levodopa dose (as levels rise and fall), with dystonic quality | Related to intermediate dopamine levels — partial receptor stimulation |
| Off-period dystonia | Painful sustained muscle contractions, typically in the feet/legs, often early morning before first dose | Low dopamine levels → loss of basal ganglia inhibition of dystonic postures |
| Freezing of gait | Sudden inability to initiate or continue walking | Complex; involves non-dopaminergic pathways (often resistant to levodopa adjustment) |
| Strategy | Mechanism | Application |
|---|---|---|
| Fractionate levodopa (smaller doses, more frequently) | Smoother plasma levels → less pulsatile stimulation | Wearing-off |
| Add COMT inhibitor (entacapone/opicapone) | ↑ Levodopa bioavailability and half-life | Wearing-off |
| Add MAO-B inhibitor (rasagiline/safinamide) | ↓ Dopamine breakdown → prolongs "on" time | Wearing-off |
| Add dopamine agonist | Longer half-life → smoother stimulation; adjunctive effect | Wearing-off; allows levodopa dose reduction |
| Controlled-release levodopa (Madopar HBS, Sinemet CR) | Slower absorption → more sustained plasma levels | Nocturnal "off" periods; wearing-off |
| Dispersible levodopa (Madopar dispersible) | Rapid absorption for "rescue" during "off" periods | Unpredictable "off" episodes; early morning akinesia |
| Reduce individual levodopa dose | Lower peak levels → less peak-dose dyskinesia | Peak-dose dyskinesia |
| Amantadine | NMDA antagonism → reduce dyskinesia | Peak-dose dyskinesia |
| Advanced therapies (see below) | Continuous dopaminergic stimulation | Refractory motor complications |
5. Advanced Therapies
For patients with refractory motor complications despite optimal oral medication adjustment, three advanced therapies are available:
DBS is FDA-approved for essential tremor, Parkinson's disease, dystonia, and OCD [2].
Principle: High-frequency electrical stimulation of a deep brain target disrupts pathological neuronal firing patterns. In iPD, stimulation of the STN or GPi modulates the overactive indirect pathway, mimicking the effect of dopamine on basal ganglia circuitry.
Patient selection criteria [2]:
| Criterion | Rationale |
|---|---|
| Idiopathic PD (not Parkinson-plus) | Parkinson-plus syndromes do not respond to DBS because the pathology extends beyond the nigrostriatal pathway |
| Advanced disease: > 5 years since diagnosis | Ensures diagnostic certainty (Parkinson-plus often declared within 5 years) |
| Excellent response to levodopa | Predicts response to DBS [2] — if levodopa works, the postsynaptic circuits are intact and can respond to DBS modulation |
| Motor fluctuations from levodopa therapy despite optimal treatment (e.g. peak-dose dyskinesia) | This is the primary indication — DBS smooths out fluctuations |
| Age ≤ 75 | Older patients have more comorbidities and cognitive decline that limit benefit |
| UPDRS motor score > 30/108 at off state | Significant motor disability in "off" state |
| Hoehn-and-Yahr grade ≥ 3 | At least moderate bilateral disease |
Contraindications [2]:
| Contraindication | Why |
|---|---|
| Parkinson-plus syndrome | Will not respond — pathology beyond nigrostriatal |
| Mentally unfit (MMSE < 24/30, comorbid psychiatric problem, dementia) | DBS can worsen cognitive function and mood; patients need to cooperate with programming |
| Coagulopathy, medically unfit | Surgical risk |
| Remote area difficult for adjustment or battery review | DBS requires regular follow-up for programming optimisation and battery replacement |
Sites of implantation [2]:
| Target | Best For | Mnemonic |
|---|---|---|
| Subthalamic nucleus (STN) | Controlling tremor and rigidity (PD) | STN = Standard Target for Neuro (motor symptoms) |
| Globus pallidus interna (GPi) | Controlling dyskinesia / dystonia ("i for inhibition") [2] | GPi = "i" for inhibiting dyskinesias |
| Ventral intermediate nucleus of thalamus (VIM) | Tremor (especially essential tremor) | Less commonly used in PD; mainly for tremor-dominant cases |
| Pedunculopontine nucleus (PPN) | Gait freezing (experimental) |
Procedure [2]:
- Pre-operative: Madopar challenge test (confirms levodopa responsiveness), MMSE, assessment by psychiatrist
- Target under LA: stereotactic frame guidance, implant microelectrode and pulse generator
- Post-op: DBS can be started after a few days, adjust settings 6–8 weeks later
Principle: Continuous jejunal infusion of levodopa-carbidopa gel via a PEG-J tube. Bypasses erratic gastric emptying and provides continuous dopaminergic stimulation → markedly reduces motor fluctuations and dyskinesias.
Indication: Advanced iPD with severe motor fluctuations refractory to optimised oral therapy; alternative to DBS (especially for patients who are not DBS candidates)
Complications: PEG-J site infection, tube dislodgement, peritonitis, polyneuropathy (possibly from vitamin B6/B12 deficiency due to high-dose levodopa)
Principle: Apomorphine (potent D1/D2 agonist) delivered via a subcutaneous pump → continuous dopaminergic stimulation
Indication: Advanced iPD with severe motor fluctuations; alternative to DBS/LCIG
Complications: Subcutaneous nodules at injection sites, nausea (co-prescribe domperidone), somnolence, hallucinations
Non-motor symptoms significantly impact quality of life and are often under-treated:
| Non-Motor Symptom | Management | Mechanism / Notes |
|---|---|---|
| Depression | SSRIs (sertraline, citalopram), SNRIs; pramipexole has antidepressant effects via D3 | Avoid TCAs in elderly (anticholinergic). SSRIs generally safe; monitor for serotonin syndrome with MAO-B inhibitors |
| Anxiety | SSRIs; benzodiazepines short-term [3] | |
| PD-psychosis / hallucinations | Step-wise: ↓ amantadine / selegiline → ↓ DA agonist → ↓ levodopa → start atypical antipsychotics (clozapine) / ECT [2] | Levodopa is least likely to cause psychosis among all PD drugs [2] — so it is the last to be reduced. Pimavanserin (5-HT2A inverse agonist, no D2 blockade) is specifically approved for PD psychosis in some regions |
| PD-dementia | Cholinesterase inhibitors (rivastigmine — only one with specific PD-dementia evidence); avoid anticholinergics | Rivastigmine improves cognition and neuropsychiatric symptoms |
| REM sleep behaviour disorder | Melatonin (first-line, safer); clonazepam (second-line) [7] | Bed safety measures (remove sharp objects, mattress on floor) |
| Orthostatic hypotension | Non-pharmacological first (compression stockings, ↑ salt/fluid, rise slowly); pharmacological: midodrine (α1-agonist), fludrocortisone (mineralocorticoid) | Review PD medications that may worsen OH (levodopa, DA agonists) |
| Constipation | ↑ Fibre, ↑ fluids, exercise; bulk/osmotic laxatives (macrogol, lactulose) [3] | |
| Sialorrhoea (drooling) | Botulinum toxin injection into salivary glands; glycopyrrolate (peripheral anticholinergic); atropine sublingual drops | Due to ↓ swallowing frequency, not ↑ production |
| Excessive daytime sleepiness | Modafinil; methylphenidate [2]; review dopaminergic medications | |
| Urinary urgency/frequency | Anticholinergics (solifenacin, trospium — more uroselective); mirabegron (β3-agonist) | Avoid oxybutynin in elderly (crosses BBB → cognitive side effects) |
PD Psychosis Management Hierarchy — Must Know
The step-wise approach [2]:
- ↓ Amantadine / selegiline (highest psychosis risk per dopaminergic potency)
- ↓ Dopamine agonist
- ↓ Levodopa (last to reduce — least likely to cause psychosis)
- Start atypical antipsychotics: clozapine (gold standard — no D2 blockade in nigrostriatal pathway) or quetiapine (less evidence but better tolerated, no clozapine monitoring)
- Never use typical antipsychotics (haloperidol) — will dramatically worsen parkinsonism
- Pimavanserin — FDA-approved for PD psychosis; 5-HT2A inverse agonist with no dopamine receptor activity
| Modality | Role | Evidence/Rationale |
|---|---|---|
| Physiotherapy | Gait training, balance exercises, cueing strategies (visual/auditory cues to overcome freezing), stretching for rigidity | Strong evidence for improving gait, balance, and reducing falls. Cueing (e.g. laser pointer on walking stick, rhythmic auditory stimulation) bypasses defective basal ganglia internal cueing |
| Occupational therapy | ADL adaptation, home safety assessment, assistive devices | Maintains independence |
| Speech and language therapy (SALT) | Lee Silverman Voice Treatment (LSVT LOUD) for hypophonia; swallowing assessment for dysphagia | LSVT LOUD is the most evidence-based speech therapy for PD — trains patients to speak with effort ("think loud") |
| Exercise | Tai chi, dance (tango), cycling, boxing, walking | Strong evidence for neuroplasticity, ↑ BDNF, slowed motor decline. Tai chi specifically improves balance |
| Dietetics | High-fibre diet for constipation; protein redistribution (take levodopa 30 min before meals — dietary protein competes for the same amino acid transporter) | Protein redistribution can improve levodopa absorption |
| Psychosocial support | Counselling, support groups, carer education | Depression, anxiety, carer burnout are major issues |
| Palliative care | In advanced disease — symptom management, advance care planning, end-of-life care | iPD is ultimately a terminal illness with median survival ~13 years from onset [3] |
| Drug Class | Drugs | Mechanism | Main Use | Key Side Effects |
|---|---|---|---|---|
| Levodopa + DDI | Madopar, Sinemet | Dopamine precursor + peripheral decarboxylase inhibitor | Gold standard; all stages | Motor complications (long-term), nausea, OH, psychosis |
| DA Agonists | Pramipexole, ropinirole, rotigotine, apomorphine | Direct D2/D3 receptor stimulation | Early monotherapy (young); adjunct | ICDs, somnolence, hallucinations, oedema |
| MAO-B Inhibitors | Selegiline, rasagiline, safinamide | ↓ Dopamine metabolism | Early monotherapy; adjunct for wearing-off | Insomnia, nausea; serotonin syndrome risk with pethidine |
| COMT Inhibitors | Entacapone, tolcapone, opicapone | ↓ Peripheral levodopa metabolism | Adjunct for wearing-off (always with levodopa) | Dyskinesias, diarrhoea, hepatotoxicity (tolcapone) |
| Anticholinergics | Trihexyphenidyl, benztropine | ↓ Relative cholinergic excess | Tremor-dominant in young patients | Cognitive decline, dry mouth, urinary retention, glaucoma |
| Amantadine | Amantadine | NMDA antagonism + ↑ DA release | Levodopa-induced dyskinesia; mild early PD | Livedo reticularis, oedema, confusion |
| Scenario | Best Approach |
|---|---|
| Young patient (< 65), mild symptoms | MAO-B inhibitor or DA agonist monotherapy; delay levodopa |
| Older patient (≥ 70), significant disability | Start levodopa + DDI (gold standard) |
| Tremor-dominant, young | Consider anticholinergic (if no cognitive impairment) or DA agonist |
| Wearing-off | Add COMT inhibitor / MAO-B inhibitor / DA agonist; fractionate levodopa |
| Peak-dose dyskinesia | ↓ Individual levodopa dose; add amantadine; consider DBS |
| PD psychosis | Step-wise drug reduction; clozapine / pimavanserin |
| PD dementia | Rivastigmine; stop anticholinergics |
| Refractory motor fluctuations | DBS, LCIG (Duodopa), or apomorphine infusion |
| Drug-induced parkinsonism | Stop offending drug; do NOT add levodopa |
High Yield Summary
No disease-modifying therapy exists — all treatment is symptomatic.
Levodopa + DDI (Madopar/Sinemet) = gold standard, most effective for motor symptoms. Always given with peripheral decarboxylase inhibitor.
Younger patients (< 65): Consider DA agonist or MAO-B inhibitor first to delay motor complications.
Motor complications (wearing-off, dyskinesia): Fractionate levodopa, add COMT/MAO-B inhibitor, add DA agonist, amantadine for dyskinesia, consider DBS/LCIG/apomorphine infusion.
DBS: For iPD with > 5 years disease duration, excellent levodopa response, motor fluctuations despite optimal oral therapy, age ≤ 75, MMSE ≥ 24. STN for tremor/rigidity; GPi for dyskinesia.
PD psychosis step-down: ↓ amantadine/selegiline → ↓ DA agonist → ↓ levodopa (least likely cause) → clozapine/pimavanserin. Never use typical antipsychotics.
Non-motor symptom management: Rivastigmine for PD dementia, SSRIs for depression, melatonin/clonazepam for RBD, midodrine/fludrocortisone for OH.
MDT essential: Physio (gait training, cueing), OT, SALT (LSVT LOUD), exercise (tai chi), dietetics (protein redistribution).
Active Recall - Management of Idiopathic Parkinson Disease
References
[1] Lecture slides: GC 091. Unsteady gait cerebellar lesions; movement disorders; Parkinsonism.pdf [2] Senior notes: Maksim Medicine Notes.pdf (Neurology – Parkinsonism, p.248–252) [3] Senior notes: Ryan Ho Neurology.pdf (Section 5.2.2 iPD management, p.121) [4] Senior notes: learning_points_output.txt (Neurology – Two Cases of Movement Disorders) [7] Senior notes: Ryan Ho Psychiatry.pdf (Section 4.2.5 DLB treatment, p.95) [13] AOS material: AOS - Geriatrics.pdf (Medication Management case, p.14)
Complications of Idiopathic Parkinson Disease
Complications of iPD arise from three interrelated sources: (1) the disease itself (progressive neurodegeneration), (2) treatment (particularly long-term levodopa therapy), and (3) interaction between disease progression and ageing. Understanding which complications come from the disease versus the drugs is critical for management — because the approach differs fundamentally.
1. Motor Complications of Disease Progression
These complications arise because neurodegeneration is relentless — the disease progresses regardless of treatment.
- Postural instability is a late feature of iPD [2] and is least responsive to dopaminergic therapy [2]
- Why? Postural control depends on non-dopaminergic systems (cholinergic pedunculopontine nucleus, noradrenergic locus coeruleus, serotonergic raphe nuclei) that are also degenerating but are NOT addressed by dopamine replacement
- Falls are the single most important cause of morbidity in advanced iPD — leading to hip fractures, subdural haematomas, and hospitalisation
- Compounded by orthostatic hypotension (both disease-related autonomic dysfunction and medication-related)
Carbidopa/levodopa can cause falls through orthostatic hypotension [13] — always consider medication contribution to falls in elderly PD patients.
Consequences of falls:
- Fractures (especially hip — #NOF)
- Head injury → subdural haematoma (these patients are often frail and may be on anticoagulants)
- Fear of falling → activity restriction → deconditioning → worsening disability (vicious cycle)
- Loss of independence, institutionalisation
- Sudden, transient inability to move the feet, typically at doorways, turns, narrow spaces, or when approaching a target
- Affects ~50% of patients after 5 years and ~80% after 10 years
- Pathophysiology: Disruption of supplementary motor area and basal ganglia locomotor circuits, involving both dopaminergic and non-dopaminergic pathways — hence often resistant to levodopa adjustment
- FOG is a major precipitant of falls
- Management: Visual cueing (laser pointer, lines on floor), auditory cueing (metronome, rhythmic music), physiotherapy, optimising dopaminergic therapy
- Oropharyngeal bradykinesia and rigidity → impaired coordination of the swallowing mechanism → silent aspiration, choking
- Develops in ~80% of patients by the advanced stage
- Aspiration pneumonia is the leading cause of death in iPD [3]
The most common cause of death in DLB/PD spectrum is failure to thrive, followed by pneumonia and swallowing difficulties, other medical conditions, and complications from a fall [14].
- Why aspiration pneumonia kills: Weakened cough reflex (brainstem degeneration) + impaired airway protection (laryngeal rigidity/bradykinesia) + reduced mobility (poor chest expansion, secretion clearance) → recurrent aspiration → pneumonia → sepsis
- Management: SALT assessment, modified diet textures, postural techniques during eating, PEG tube in advanced disease (controversial — does not clearly improve survival), chest physiotherapy
- Low-volume, monotonous, tremulous speech (microphonia) [2] worsens progressively
- Palilalia (involuntary repetition of syllables/words) may develop
- Impact: social isolation, depression, reduced quality of life, difficulty communicating needs (especially important in institutional care)
- Management: Lee Silverman Voice Treatment (LSVT LOUD); communication aids in advanced stages
2. Motor Complications of Treatment (Levodopa-Related)
These are the most important treatment-related complications and the main driver of management changes in established iPD. They typically emerge after 5–10 years of levodopa therapy.
- Motor symptoms re-emerge before the next dose of levodopa is due
- Pathophysiology: As more dopaminergic terminals are lost, the remaining terminals cannot store and release dopamine steadily. The therapeutic effect becomes directly dependent on the plasma half-life of levodopa (~90 minutes). The "on" period shortens progressively.
- Earliest motor complication; affects ~50% at 5 years, ~80% at 10 years
- Can also involve non-motor wearing-off: anxiety, pain, dysphoria, sweating returning before next dose
- Unpredictable, sudden switching between "on" (mobile, functional) and "off" (akinetic, rigid, immobile) states, not clearly related to dosing schedule
- Pathophysiology: Severely depleted dopaminergic terminals + erratic levodopa absorption + postsynaptic receptor changes → unpredictable dopamine levels in the striatum
- Very distressing — patients can "freeze" suddenly mid-activity
| Type | Timing | Character | Mechanism |
|---|---|---|---|
| Peak-dose dyskinesia | At peak plasma levodopa level (typically 30–90 min after dose) | Choreiform (flowing, dance-like involuntary movements), usually involving head, trunk, and limbs | Hypersensitised, denervated D1 receptors are excessively stimulated at peak dopamine levels |
| Diphasic dyskinesia | At the beginning and end of each dose cycle (as levels rise and fall) | Often dystonic and repetitive; may be ballistic; typically involves legs | Related to intermediate dopamine concentrations causing partial receptor activation |
| Off-period dystonia | When dopamine levels are lowest (typically early morning before first dose) | Painful sustained muscle contractions, especially foot dystonia (plantar flexion, inversion) | Loss of dopaminergic inhibition of dystonic circuits at very low dopamine |
- Risk factors for earlier LID development: younger age of onset (more years of therapy, more plastic receptors), higher levodopa dose, lower body weight, female sex
- LID can become as disabling as the parkinsonism itself — some patients prefer to be "off" rather than dyskinetic
| Complication | Strategy |
|---|---|
| Wearing-off | Fractionate levodopa, add COMT-i/MAO-B-i/DA agonist, CR formulations |
| On-off | Continuous drug delivery (LCIG, apomorphine pump), DBS |
| Peak-dose dyskinesia | Reduce individual levodopa dose, amantadine, DBS (GPi target) |
| Diphasic dyskinesia | Difficult; try increasing individual dose to "jump through" the intermediate level |
| Off-period dystonia | Early morning dispersible levodopa; CR levodopa at bedtime |
3. Neuropsychiatric Complications
These are among the most disabling and distressing complications for patients and carers alike.
- PD-dementia affects 10–15% of PD patients at any time point [3], but cumulative risk reaches up to 80% after 20 years of disease
- Pathophysiology: Cortical Lewy body spread (Braak stages 5–6) + degeneration of the cholinergic nucleus basalis of Meynert + mesocortical dopamine depletion
- Profile: Subcortical dementia — executive dysfunction, slowed processing, visuospatial impairment, attention deficits. Memory retrieval is impaired but recognition may be relatively preserved (unlike AD where encoding itself is lost)
- Drugs that may worsen cognitive function: anticholinergic drugs and dopaminergic drugs for motor symptoms of PD [6]
- PD-dementia is worsened by anticholinergics [3] — this is why anticholinergics are absolutely contraindicated in elderly PD patients with cognitive impairment
Management of PD dementia: Cholinesterase inhibitors (e.g. rivastigmine, donepezil), memantine [6]. No therapies have been shown to modify the course of the disease or influence prognosis [6] — all treatment is symptomatic.
Anticholinergics and PD Dementia
Anticholinergic drugs worsen cognitive function in PD [6]. This is a must-know drug-disease interaction [13]. If a PD patient develops cognitive decline, immediately review and stop all anticholinergics (including trihexyphenidyl, oxybutynin, amitriptyline, and other drugs with anticholinergic burden).
- PD-psychosis is common in late stages, can be due to levodopa/DA agonists and the disease itself [3]
- Spectrum: frightening nightmares → vivid dreams → formed visual illusions → visual hallucinations (often benign "passage hallucinations" initially) → paranoid delusions → delirium
- Pathophysiology: Multifactorial — cortical Lewy body pathology (serotonergic/cholinergic deficit) + dopaminergic medication overstimulation of mesolimbic/mesocortical pathways + advanced age + cognitive impairment
- Manifestations: frightening nightmares, vivid dreams/illusions, overt mania, visual hallucinations, delusions [3]
Management of PD psychosis: Reduce dose or even stop PD meds (monitor motor functions). Start antipsychotics if inadequate response (e.g. pimavanserin) [6].
- Remember the step-wise drug reduction hierarchy: ↓ amantadine/selegiline → ↓ DA agonist → ↓ levodopa (levodopa is least likely to cause psychosis) → add clozapine or pimavanserin [2]
- Depression affects > 50% of iPD patients [3] — making it one of the most common non-motor complications
- Pathophysiology: Degeneration of serotonergic (raphe nuclei), noradrenergic (locus coeruleus), and dopaminergic (mesolimbic) systems — this is a true neurobiological depression, not merely "reactive" to disability
- Associated with serotonergic deficiency, can consider SSRIs [3]
- Anxiety is also extremely common and may be part of non-motor wearing-off
- Under-recognised and under-treated — significantly impacts quality of life
- Pathological gambling, hypersexuality, compulsive shopping, binge eating, punding (repetitive purposeless behaviours)
- Prevalence: ~15–20% of patients on dopamine agonists
- Pathophysiology: D3 receptor stimulation in the mesolimbic "reward" pathway by dopamine agonists → abnormal reward-seeking behaviour
- Can be devastating — financial ruin, relationship breakdown, legal consequences
- Management: Reduce or stop the DA agonist; this is the most effective intervention. Screen actively at every follow-up.
- A specific subtype of ICD where patients compulsively take excessive levodopa despite worsening dyskinesias
- Essentially a "dopamine addiction" — patients escalate doses far beyond therapeutic need because of the euphoria associated with the "on" state
- More common in young-onset PD, male, history of mood disorders or substance use
- Management: Structured drug dosing, reduce total dopaminergic load, psychiatric support
These arise from Lewy body pathology in the autonomic nervous system (dorsal motor nucleus of the vagus, intermediolateral cell column of the spinal cord, peripheral autonomic ganglia).
| Complication | Pathophysiology | Clinical Impact | Management |
|---|---|---|---|
| Orthostatic hypotension | Postganglionic sympathetic denervation → ↓ noradrenaline release → failure to vasoconstrict on standing. Worsened by levodopa/DA agonists | Dizziness, syncope, falls (most likely cause of fall in a PD patient on carbidopa/levodopa [13]) | Non-pharmacological (compression stockings, ↑ salt/fluid, rise slowly, elevate head of bed); pharmacological: midodrine, fludrocortisone, droxidopa |
| Constipation | Lewy pathology in enteric nervous system + dorsal vagal nucleus → ↓ gut motility. Worsened by anticholinergics | Chronic, severe; can cause pseudo-obstruction | High fibre, ↑ fluids, exercise, macrogol/lactulose [3] |
| Gastroparesis | Neurological disease (e.g. Parkinsonism) is a recognised cause of gastroparesis [15] — vagal nerve dysfunction → delayed gastric emptying | Nausea, bloating, vomiting, erratic levodopa absorption (worsens motor fluctuations) | Small frequent meals, prokinetics (domperidone — NOT metoclopramide), optimise levodopa formulation |
| Urinary dysfunction | Detrusor hyperactivity (loss of dopaminergic inhibition of pontine micturition centre) | Frequency, urgency, nocturia, incontinence | Uroselective anticholinergics (solifenacin, trospium); mirabegron; avoid oxybutynin |
| Sexual dysfunction | Autonomic neuropathy (erectile dysfunction); ↓ libido from dopamine depletion; paradoxically, DA agonists can cause hypersexuality | ED, loss of libido, or ICD-related hypersexuality | Sildenafil for ED; reduce DA agonist if hypersexuality |
| Excessive sweating | Hypothalamic dopamine depletion → thermoregulatory dysfunction | Episodes of profuse sweating, often linked to "off" periods; associated with seborrhoeic dermatitis [3] | Optimise motor fluctuations; botulinum toxin for focal hyperhidrosis |
| Sialorrhoea (drooling) | ↓ Frequency of automatic swallowing (oropharyngeal bradykinesia), NOT ↑ production | Social embarrassment, perioral dermatitis, aspiration risk | Botulinum toxin to salivary glands; glycopyrrolate; sublingual atropine |
Important Drug-Disease Interaction
Parkinson's disease and metoclopramide — this is a clinically important drug-disease interaction [13]. Metoclopramide is a D2 antagonist that crosses the BBB and will dramatically worsen parkinsonism. Never use metoclopramide in PD patients. Use domperidone instead (peripheral D2 antagonist, does not significantly cross the BBB).
| Complication | Prevalence | Pathophysiology | Management |
|---|---|---|---|
| REM sleep behaviour disorder (RBD) | 30–60% of iPD | Loss of normal REM atonia (sublaterodorsal nucleus degeneration) → acting out dreams | Bed safety; melatonin (first-line); clonazepam [7] |
| Insomnia | ~60% | Multifactorial: nocturia, rigidity/akinesia preventing turning in bed, pain, depression, medication effects | Sleep hygiene; treat underlying cause; consider CR levodopa at bedtime for nocturnal akinesia |
| Excessive daytime sleepiness (EDS) | 15–50% | Degeneration of wake-promoting nuclei (hypothalamic orexin/hypocretin neurons); DA agonist side effect | Review medications; modafinil; methylphenidate [2] |
| Sleep fragmentation | Very common | Off-period immobility, restless legs, vivid dreams | Optimise nocturnal dopaminergic coverage |
| Sleep attacks | Rare but dangerous | Sudden irresistible sleepiness, especially with DA agonists | Driving precautions; reduce/change DA agonist |
DBS complications [2]:
| Category | Complications |
|---|---|
| Surgery | Intracranial haemorrhage (ICH), infection, bleeding |
| Hardware | Lead migration, lead fracture, skin erosion (over the pulse generator or extension cables) |
| Stimulation | Dysarthria, paraesthesia (from current spread to adjacent structures) |
| Neuropsychiatric | Depression, psychosis, memory decline (especially with STN stimulation, which can affect limbic circuits) |
- Hardware-related complications require surgical revision
- Stimulation-related side effects can often be managed by adjusting DBS programming parameters (changing contact, frequency, voltage)
- Impulse generator battery depletion requires surgical replacement (every ~3–5 years for non-rechargeable; ~15 years for rechargeable)
7. Other Complications
| Complication | Mechanism |
|---|---|
| Osteoporosis and fractures | Immobility, vitamin D deficiency (reduced sun exposure), falls, possible dopamine-related effects on bone metabolism |
| Frozen shoulder | Rigidity → reduced shoulder ROM → adhesive capsulitis; may be an early presenting feature |
| Camptocormia | Marked forward flexion of the trunk; likely due to dystonia of paraspinal muscles |
| Pisa syndrome | Sustained lateral trunk flexion; can be drug-related (DA agonists) |
| Contractures | Late-stage rigidity → fixed joint deformities (especially the striatal hand/foot) |
- Weight loss — multifactorial: dyskinesias increase energy expenditure; dysphagia reduces oral intake; gastroparesis causes nausea/early satiety; depression reduces appetite
- Malnutrition → sarcopenia → further weakness and fall risk → vicious cycle
- Vitamin B12/B6 deficiency — associated with high-dose levodopa therapy (levodopa metabolism consumes these vitamins); may contribute to peripheral neuropathy
- Clinical course: insidious onset with gradual progression over 10–15 years [3]
- Untreated → ↓ UPDRS motor score 8–9% per year [3]
- Mortality rate 2–5× general population matched for age [3]
- Average survival from onset = 13 years [3]
- Often die from complications e.g. pneumonia [3] (aspiration pneumonia is the leading cause of death)
- Better prognosis: tremor-dominant subtype, younger onset, female sex
- Worse prognosis: PIGD subtype (akinetic-rigid), older onset, early cognitive impairment, early autonomic failure
| Category | Key Complications |
|---|---|
| Disease progression — motor | Postural instability, falls, freezing of gait, dysphagia/aspiration, dysarthria |
| Treatment-related — motor | Wearing-off, on-off fluctuations, peak-dose dyskinesia, diphasic dyskinesia, off-period dystonia |
| Neuropsychiatric | PD dementia, PD psychosis, depression, anxiety, ICDs, dopamine dysregulation syndrome |
| Autonomic | Orthostatic hypotension, constipation, gastroparesis, urinary dysfunction, sexual dysfunction, sweating, sialorrhoea |
| Sleep | RBD, insomnia, EDS, sleep attacks |
| DBS-related | ICH, infection, lead migration, dysarthria, neuropsychiatric |
| Musculoskeletal | Fractures, osteoporosis, frozen shoulder, camptocormia, contractures |
| Nutritional | Weight loss, malnutrition, B12/B6 deficiency |
| Cause of death | Aspiration pneumonia (commonest), falls/fractures, failure to thrive |
High Yield Summary
Motor complications of treatment emerge after 5–10 years of levodopa: wearing-off (earliest, commonest), on-off fluctuations, peak-dose dyskinesia, off-period dystonia. They arise because progressive nigrostriatal denervation removes the dopamine "buffering" capacity, making striatal dopamine levels mirror pulsatile plasma levodopa levels.
PD dementia affects up to 80% cumulatively. Anticholinergics worsen it — stop them. Treat with rivastigmine. No disease-modifying therapy exists.
PD psychosis stepwise management: ↓ amantadine/selegiline → ↓ DA agonist → ↓ levodopa (last) → clozapine/pimavanserin. Never use typical antipsychotics.
Aspiration pneumonia is the leading cause of death in iPD — from oropharyngeal bradykinesia causing dysphagia and silent aspiration.
Orthostatic hypotension is a major complication causing falls — both disease-related (postganglionic denervation) and drug-related (levodopa, DA agonists).
Never use metoclopramide in PD — use domperidone instead. Metoclopramide crosses the BBB and blocks D2 receptors, worsening parkinsonism.
DBS complications: ICH, infection, lead migration, stimulation-induced dysarthria/paraesthesia, neuropsychiatric effects.
Prognosis: Average survival ~13 years from onset; mortality 2–5× age-matched general population.
Active Recall - Complications of Idiopathic Parkinson Disease
References
[2] Senior notes: Maksim Medicine Notes.pdf (Neurology – Parkinsonism, p.248–253) [3] Senior notes: Ryan Ho Neurology.pdf (Section 5.2.2 iPD clinical features and prognosis, p.121–125) [6] Lecture slides: GC 037. Common neurological problems in older people.pdf (Management of PDD, p.65) [7] Senior notes: Ryan Ho Psychiatry.pdf (Section 4.2.5 DLB treatment, p.95) [13] AOS material: AOS - Geriatrics.pdf (Medication Management case p.14; Drug-disease interactions p.19) [14] Lecture slides: GC 241. Reference (3) - Patel dementia with lewy bodies.pdf (p.20) [15] Senior notes: Block A - Indigestion and 'heartburn'_ nausea and vomiting; gastric motility problems; benign esophageal lesions.pdf (Gastroparesis causes, p.26)
High Yield Summary
Definition: iPD is a chronic progressive neurodegenerative disease caused by loss of dopaminergic neurons in the SNpc, with Lewy body pathology.
Epidemiology: Prevalence ~1% over 65; M > F; peak onset 6th decade; 5–10% familial.
Pathology: Degeneration of SNpc → ↓ striatal dopamine → overactive indirect pathway → ↓ thalamic excitation of motor cortex. Lewy bodies (α-synuclein) spread caudal-to-rostral (Braak staging).
Genetics: LRRK2 = most common monogenic (AD); Parkin = most common early-onset (AR); GBA = most common genetic risk factor.
Cardinal motor features (TRAP): Bradykinesia (mandatory) + rest tremor and/or rigidity. Postural instability is late.
Non-motor features precede motor by 10–20 years: Anosmia, constipation, RBD, depression, fatigue.
Key distinctions: PD tremor is resting (4–6 Hz), asymmetric, with re-emergence after 5-second latency. Essential tremor is action/postural (6–12 Hz), symmetric, no latency, improved by alcohol.
Red flags for NOT iPD: Symmetric onset, early falls, early dementia, prominent autonomic failure, cerebellar/pyramidal signs, poor levodopa response, downward gaze palsy.
Drug-induced parkinsonism is reversible — always check drug history!
High Yield Summary
Framework: 80% of parkinsonism = iPD. The remaining 20% = drug-induced, Parkinson-plus (MSA, PSP, CBD, DLB), vascular, metabolic (Wilson's), toxic (CO, Mn, MPTP), structural (NPH, tumours), infections (post-encephalitic), and inherited (Huntington's).
First step: Always check medication history — DIP is the most common reversible cause.
Red flags against iPD: Bilateral symmetric onset, early falls/bulbar symptoms/autonomic failure, downward gaze palsy, cerebellar signs, cortical sensory loss, pyramidal signs, poor levodopa response, rapid progression.
Absolute exclusions for iPD: Cerebellar abnormality, downward supranuclear gaze palsy, normal DaTscan, FTD within 5 years, lower limb restriction ≥ 3 years, cortical sensory loss/apraxia.
Key Parkinson-plus distinctions: MSA = cerebellar/autonomic + oligodendroglial α-synuclein; PSP = downward gaze palsy + early falls + tau; CBD = alien limb + apraxia + tau; DLB = early dementia + visual hallucinations + RBD + cortical Lewy bodies.
Essential tremor is NOT parkinsonism — action/postural tremor, no bradykinesia, no rigidity, symmetric, alcohol-responsive, high-frequency (6–12 Hz).
High Yield Summary
iPD is a clinical diagnosis using MDS criteria: Bradykinesia (mandatory) + rest tremor or rigidity → then apply supportive criteria, red flags, and absolute exclusion criteria.
Clinically established iPD = ≥ 2 supportive criteria + no red flags + no exclusion criteria.
Supportive criteria: Dramatic levodopa response, levodopa-induced dyskinesia, rest tremor, anosmia/cardiac MIBG denervation.
Absolute exclusion criteria: Cerebellar signs, downward gaze palsy, cortical sensory loss/apraxia, normal DaTscan, no levodopa response, FTD within 5 years, lower-limb-only PD ≥ 3 years, DIP.
Investigation hierarchy:
- Bedside: gait, vertical gaze, cerebellar signs, BP, pull test, MoCA, drug history
- Bloods: CBC, LRFT, TFT, ceruloplasmin (if < 50), B12
- MRI brain: exclude structural causes; specific signs (hummingbird = PSP, hot cross bun = MSA-C, putaminal rim = MSA-P)
- DaTscan: distinguishes neurodegenerative (abnormal) from non-degenerative (normal) parkinsonism; does NOT distinguish iPD from Parkinson-plus
- Cardiac MIBG: distinguishes iPD/DLB (reduced) from MSA (normal)
- Levodopa trial: dramatic response = strong supportive criterion
Emerging: α-synuclein SAA in CSF (high sensitivity/specificity for synucleinopathies); α-synuclein skin biopsy (> 92% sensitivity).
High Yield Summary
No disease-modifying therapy exists — all treatment is symptomatic.
Levodopa + DDI (Madopar/Sinemet) = gold standard, most effective for motor symptoms. Always given with peripheral decarboxylase inhibitor.
Younger patients (< 65): Consider DA agonist or MAO-B inhibitor first to delay motor complications.
Motor complications (wearing-off, dyskinesia): Fractionate levodopa, add COMT/MAO-B inhibitor, add DA agonist, amantadine for dyskinesia, consider DBS/LCIG/apomorphine infusion.
DBS: For iPD with > 5 years disease duration, excellent levodopa response, motor fluctuations despite optimal oral therapy, age ≤ 75, MMSE ≥ 24. STN for tremor/rigidity; GPi for dyskinesia.
PD psychosis step-down: ↓ amantadine/selegiline → ↓ DA agonist → ↓ levodopa (least likely cause) → clozapine/pimavanserin. Never use typical antipsychotics.
Non-motor symptom management: Rivastigmine for PD dementia, SSRIs for depression, melatonin/clonazepam for RBD, midodrine/fludrocortisone for OH.
MDT essential: Physio (gait training, cueing), OT, SALT (LSVT LOUD), exercise (tai chi), dietetics (protein redistribution).
High Yield Summary
Motor complications of treatment emerge after 5–10 years of levodopa: wearing-off (earliest, commonest), on-off fluctuations, peak-dose dyskinesia, off-period dystonia. They arise because progressive nigrostriatal denervation removes the dopamine "buffering" capacity, making striatal dopamine levels mirror pulsatile plasma levodopa levels.
PD dementia affects up to 80% cumulatively. Anticholinergics worsen it — stop them. Treat with rivastigmine. No disease-modifying therapy exists.
PD psychosis stepwise management: ↓ amantadine/selegiline → ↓ DA agonist → ↓ levodopa (last) → clozapine/pimavanserin. Never use typical antipsychotics.
Aspiration pneumonia is the leading cause of death in iPD — from oropharyngeal bradykinesia causing dysphagia and silent aspiration.
Orthostatic hypotension is a major complication causing falls — both disease-related (postganglionic denervation) and drug-related (levodopa, DA agonists).
Never use metoclopramide in PD — use domperidone instead. Metoclopramide crosses the BBB and blocks D2 receptors, worsening parkinsonism.
DBS complications: ICH, infection, lead migration, stimulation-induced dysarthria/paraesthesia, neuropsychiatric effects.
Prognosis: Average survival ~13 years from onset; mortality 2–5× age-matched general population.
Frontotemporal Dementia
Frontotemporal dementia is a group of neurodegenerative disorders characterized by progressive atrophy of the frontal and temporal lobes, leading to prominent changes in personality, behavior, and language with relative preservation of memory in early stages.
Parkinson Plus Syndromes
Parkinson Plus Syndromes are a group of neurodegenerative disorders that share parkinsonian features such as bradykinesia and rigidity but are distinguished by additional neurological signs—including early autonomic failure, cerebellar ataxia, supranuclear gaze palsy, or cortical dysfunction—and typically respond poorly to levodopa.