Why it matters: Chalazion vs stye is a classic exam discriminator. A chalazion is a granulomatous reaction to trapped meibomian secretion (chronic, non-tender), while a stye is an acute bacterial infection (tender, red, warm). If a chalazion recurs in the same spot in an elderly patient, consider sebaceous gland carcinoma – a rare but important "can't-miss." ^[1][7]

Think about:

• Periorbital cellulitis (preseptal) – infection anterior to orbital septum; eyelid erythema, swelling, warmth, but no proptosis, no ophthalmoplegia, no vision change
• Orbital cellulitis – infection posterior to septum; proptosis, restricted eye movements, reduced vision, pain on eye movement → ophthalmic emergency, needs IV antibiotics + CT orbit
• Allergic oedema (angioedema) – bilateral, non-tender, associated with urticaria elsewhere
• Blepharitis – chronic lid margin inflammation, crusting at lash bases, bilateral

This is one of the highest-yield sections. The lecture distinguishes:

Bilateral red eye with discharge:

• Viral conjunctivitis – watery discharge, follicles on tarsal conjunctiva, preauricular lymphadenopathy, often post-URTI. Adenovirus most common. ^[7]
• Allergic conjunctivitis – itchy, watery, papillae on tarsal conjunctiva, bilateral, atopic history
• Bacterial conjunctivitis – mucopurulent discharge, morning crusting, one eye then the other

Unilateral red eye with minimal discharge, mild tearing:

Ask: Pain? Loss of vision? Photophobia? ^[1]

This trio of questions is critical because they separate benign from sight-threatening:

Unilateral red eye associated with: Loss of vision (acute), periorbital pain, headache, malaise, nausea/vomiting → Think acute angle-closure glaucoma (AACG). ^[1]

Why AACG presents this way: The peripheral iris bows forward and physically blocks the trabecular meshwork → aqueous humour cannot drain → IOP rises rapidly (often > 40 mmHg) → corneal oedema (hazy cornea) → pain, halos around lights, nausea/vomiting (vagal response to pain). The pupil is mid-dilated and fixed because the iris sphincter is ischaemic. ^[7][8]

Why herpes labialis recurs in the same spot: HSV-1 establishes latency in the trigeminal ganglion. Reactivation sends virus along the same nerve branch to the same dermatome area, producing vesicles at the same location. Triggers include UV light, stress, immunosuppression, fever. ^[1]

• Mucocele – painless, translucent, bluish, dome-shaped swelling on lower lip or floor of mouth; caused by rupture of minor salivary gland duct → mucin extravasation. Fluctuant.
• Ranula – a large mucocele specifically on the floor of the mouth (sublingual gland)
• Fibroma (irritation fibroma) – firm, smooth, sessile nodule on buccal mucosa along bite line; due to chronic trauma
• Oral leukoplakia – white patch that cannot be scraped off → premalignant; needs biopsy
• Oral candidiasis (thrush) – white patches that CAN be scraped off revealing red base; in immunocompromised, denture users, inhaled steroid users

• Acute pharyngitis / tonsillitis – erythematous pharynx ± exudates; viral (most common) vs bacterial (GAS – Centor criteria)
• Peritonsillar abscess (quinsy) – unilateral tonsillar swelling with uvular deviation to contralateral side, trismus, "hot potato" voice, drooling → needs urgent drainage
• Hand-foot-mouth disease – vesicles/ulcers on soft palate + hands/feet; Coxsackievirus A16 or EV71; children
• Herpangina – vesicles/ulcers on posterior palate/tonsillar pillars only (no hand/foot involvement); Coxsackievirus

• Dental abscess – localized swelling, tender, may have draining sinus; refer to dentist
• Gingivitis – swollen, erythematous, bleeding gums; associated with poor hygiene; reversible
• Periodontitis – advanced gingivitis with loss of attachment and bone; pockets > 3 mm
• Epulis – localized gingival overgrowth; differential includes pyogenic granuloma, fibrous epulis, peripheral giant cell granuloma
• Drug-induced gingival hyperplasia – phenytoin, ciclosporin, nifedipine

Acne Vulgaris:

• Pathogenesis: ↑sebum production (androgens) → follicular hyperkeratinization → C. acnes colonization → inflammation
• Lesions: open comedones (blackheads), closed comedones (whiteheads), papules, pustules, nodules, cysts
• Distribution: face, chest, back (sebaceous gland-rich areas)
• Grading: mild (comedonal), moderate (papulopustular), severe (nodulocystic)

Differentiate acne from: ^[1]

This section covers seborrhoeic dermatitis vs psoriasis vs eczema vs tinea – a massively important differential.

Seborrhoeic Dermatitis:

• Greasy, yellowish scales on erythematous base
• Distribution: scalp, eyebrows, nasolabial folds, behind ears, central chest
• Caused by Malassezia yeast → inflammatory response
• In infants = "cradle cap"
• Treatment: antifungal shampoo (ketoconazole), mild topical steroid

Psoriasis (covered on body/scalp slides too ^[1]):

• Well-demarcated, raised, erythematous plaques with silvery-white scales
• Distribution: extensor surfaces (elbows, knees), scalp, sacrum, nails
• Pathognomonic: Auspitz sign (pinpoint bleeding on removal of scale – due to thin epidermis over dilated capillaries)
• Koebner phenomenon (lesions at sites of trauma)
• Nail changes: pitting, onycholysis, oil-drop sign, subungual hyperkeratosis

Eczema (Atopic Dermatitis):

• Itchy, poorly-demarcated, erythematous patches with vesicles, weeping, crusting (acute) or lichenification (chronic)
• Distribution varies by age: infants (face, extensor), children/adults (flexural)
• Associated with atopic triad (eczema, asthma, allergic rhinitis)

Tinea (Dermatophyte Infection):

• Annular, scaly patch with active, raised border and central clearing ("ringworm")
• Can affect face (tinea faciei), scalp (tinea capitis), body (tinea corporis), groin (tinea cruris), feet (tinea pedis)
• KOH preparation shows hyphae → confirms fungal infection

This is the eczema section in greater detail, including pompholyx (dyshidrotic eczema):

• Pompholyx: intensely itchy, deep-seated vesicles on palms, sides of fingers, and soles
• Often triggered by stress, heat, nickel contact
• Vesicles are "tapioca-like" – tiny, firm, deep in the skin
• Differential: tinea manuum (usually unilateral, check both hands rule – "two feet one hand" or "one hand two feet"), contact dermatitis, psoriasis (pustular)

The "two feet, one hand" pattern = tinea, not eczema. If scaling is on both feet but only one hand, think dermatophyte infection (tinea pedis + tinea manuum). Eczema would typically be bilateral and symmetrical. ^[1]

Likely showing urticaria (hives):

• Transient, migratory wheals (raised, oedematous, erythematous plaques)
• Individual lesion lasts < 24 hours (if > 24h, consider urticarial vasculitis → biopsy)
• Mechanism: mast cell degranulation → histamine release → vasodilation, oedema
• Causes: idiopathic (most), allergic (food, drug), physical (cold, pressure, cholinergic)
• Treatment: non-sedating antihistamines (cetirizine, loratadine); if severe → short course oral steroid; if anaphylaxis → IM adrenaline

Herpes Zoster (Shingles):

• Unilateral, dermatomal distribution of grouped vesicles on erythematous base
• Preceded by prodromal pain (burning, tingling) in the same dermatome
• Pathognomonic: does not cross the midline (stays in one dermatome)
• Caused by reactivation of VZV in dorsal root ganglion
• Complications: post-herpetic neuralgia (PHN), herpes zoster ophthalmicus (V1 → Hutchinson sign = vesicle on nose tip → corneal involvement likely), disseminated zoster in immunosuppressed
• Treatment: antivirals (aciclovir, valaciclovir) within 72 hours of rash onset; analgesics

This description fits Pityriasis rosea:

• Herald patch (2-5 cm, oval, salmon-coloured with collarette scale) appears first
• Followed 1-2 weeks later by multiple smaller oval patches along skin cleavage lines → "Christmas tree" pattern on the back
• Self-limiting (6-8 weeks); treatment is symptomatic (emollients, antihistamines)
• Differential: secondary syphilis (check RPR/VDRL – always consider this!), tinea corporis, guttate psoriasis

Other rashes in this slide group may include:

• Viral exanthems (measles, rubella, roseola, erythema infectiosum/fifth disease)
• Drug eruption – morbilliform (maculopapular), symmetric, onset 7-14 days after starting drug

This is the melanoma vs benign naevus discrimination section.

ABCDE criteria for melanoma:

• "Ugly duckling" sign: the mole that looks different from all the patient's other moles → suspicious ^[11]
• Subtypes (from supporting notes ^[11]): superficial spreading (most common in Caucasians), nodular (rapidly growing dome, may be amelanotic), lentigo maligna (elderly, sun-damaged), acral lentiginous (most common in HK/Asian populations) – palms, soles, subungual

In Hong Kong / Asian populations, acral lentiginous melanoma is the most common subtype. Look for irregular pigmentation on palms, soles, or under the nail. ^[1][11]

DDx of a pigmented facial lesion:

• Seborrhoeic keratosis – "stuck on" appearance, waxy surface, horn cysts; benign; most common benign skin tumour in elderly
• Dermatosis papulosa nigra – variant of seborrhoeic keratosis; small, dark papules on face of darker-skinned individuals
• Pigmented BCC – pearly edge, telangiectasia, pigmentation common in Asians ^[11]
• Melanoma – ABCDE criteria apply

Think malignancy or vascular lesion:

• Squamous cell carcinoma (SCC) – indurated nodule/plaque with hyperkeratotic or ulcerated surface, everted edge, contact bleeding; sun-exposed areas; risk factors: UV, immunosuppression, chronic wounds (Marjolin ulcer) ^[11]
• Basal cell carcinoma (BCC) – rodent ulcer with rolled pearly edge, telangiectasia, central ulceration; most common skin cancer; locally invasive, rarely metastasises ^[11]
• Pyogenic granuloma – rapidly growing, friable, bright red nodule that bleeds easily; benign vascular proliferation; often at sites of trauma
• Keratoacanthoma – rapidly growing dome-shaped nodule with central keratin plug; may mimic SCC; some consider it a well-differentiated SCC variant

DDx of painful, swollen finger joints:

• Rheumatoid arthritis – symmetrical, MCP and PIP joints, morning stiffness > 30 min, swan-neck/boutonnière deformities in chronic disease
• Osteoarthritis – DIP (Heberden nodes) and PIP (Bouchard nodes), bony swelling, first CMC joint
• Gouty tophi – firm, white/yellow deposits near joints; associated with chronic gout
• Psoriatic arthritis – asymmetric, may involve DIP, dactylitis ("sausage digit"), nail pitting, associated skin psoriasis
• Trigger finger – painful clicking/locking of finger in flexion; thickened A1 pulley

• Mallet finger – drooping DIP; extensor tendon rupture at distal phalanx; cannot actively extend DIP; caused by forced flexion injury (e.g., ball striking fingertip)
• Ganglion cyst ("There's a lump over the back of my hand") – firm, non-tender, fluctuant, transilluminant swelling, most commonly dorsum of wrist; benign, from joint capsule or tendon sheath; treatment: reassurance, aspiration, or excision if symptomatic ^[1]

• Plantar fasciitis – heel pain worst with first steps in the morning; tenderness at medial calcaneal tubercle
• Hallux valgus (bunion) – lateral deviation of great toe with medial bony prominence at 1st MTP; may be painful with shoe wear
• Gout – acutely red, hot, swollen 1st MTP (podagra); exquisitely tender; monosodium urate crystals (negatively birefringent under polarised microscopy)
• Ingrown toenail (onychocryptosis) – nail edge grows into periungual skin; pain, erythema, granulation tissue; great toe
• Verruca plantaris (plantar wart) – HPV-induced; firm, hyperkeratotic, may have black dots (thrombosed capillaries); painful on lateral compression (vs callus which hurts on direct pressure)

• Tinea pedis (athlete's foot) – interdigital maceration, scaling, fissuring between toes (especially 4th-5th web space); may be vesicular or moccasin type
• Pitted keratolysis – multiple small pits on sole; bacterial (Corynebacterium, Kytococcus); associated with hyperhidrosis and occlusive footwear; classically malodorous
• Hyperhidrosis – excessive sweating → secondary bacterial overgrowth → odour

Spot diagnoses from facial expression / appearance:

• Bell's palsy – unilateral LMN facial weakness: forehead involvement (cannot raise eyebrow), drooping mouth, inability to close eye → exposure keratitis risk. LMN vs UMN: UMN spares forehead (bilateral cortical innervation of upper face)
• Facial nerve palsy in stroke – UMN pattern: forehead sparing, contralateral limb weakness
• Myxoedema facies – coarse features, periorbital oedema, sparse outer eyebrows, dry skin → hypothyroidism
• Acromegalic facies – coarsened features, prominent brow, prognathism, large hands/feet → growth hormone excess
• Cushing facies – moon face, plethora, buffalo hump
• Thyrotoxic stare – lid retraction, exophthalmos (Graves' disease)
• Parkinson's – hypomimia (mask-like face), reduced blinking
• Down syndrome facies – epicanthic folds, flat nasal bridge, protruding tongue, upslanting palpebral fissures → Trisomy 21

This slide addresses recognising patients who may have intellectual disability or genetic syndromes from their appearance:

• Down syndrome (Trisomy 21) – as above + single palmar crease, sandal gap, cardiac defects
• Turner syndrome (45,X) – short stature, webbed neck, wide-spaced nipples, lymphoedema in neonates
• Marfan syndrome – tall, long limbs, arachnodactyly, high-arched palate, lens subluxation, aortic root dilation
• Neurofibromatosis Type 1 – café-au-lait spots ( ≥ 6, each ≥ 15 mm in adults), axillary freckling, neurofibromas, Lisch nodules ^[13]