Skin Rash
A skin rash is a visible change in the color, texture, or appearance of the skin, often manifesting as redness, bumps, or lesions, resulting from inflammatory, infectious, allergic, or systemic causes.
Murtagh Diagnostic Strategy
| Category | Diagnosis | Key Discriminator | Cantonese Question / Finding |
|---|---|---|---|
| Probability Diagnosis | Atopic eczema | Chronic relapsing itch, flexural, atopic hx, ill-defined border [1] | 「紅疹係咪喺手踭窩、膝頭窩嗰啲位？」(Flexural?) |
| Contact dermatitis (allergic / irritant) | Well-demarcated, distribution follows exposure [6] | 「有冇用新嘅護膚品、首飾、洗潔精？」 | |
| Psoriasis | Well-demarcated erythematous plaque, silvery scale, extensor, nail pitting [1] | 「啲紅疹有冇銀色嘅皮屑？指甲有冇凹凹窿窿？」 | |
| Urticaria | Transient wheals ( < 24h each), raised, itchy [1] | 「每粒紅疹出完幾耐消？係咪24小時內會消？」 | |
| Tinea corporis | Annular, central clearing, scaly edge, KOH +ve | 「係咪中間正常、邊邊紅同甩皮？」 | |
| Serious Not To Miss | SJS/TEN | Fever > 39°C, prodromal flu, painful maculopapular → sheet-like detachment, Nikolsky +ve, mucosal involvement [5] | 「有冇發高燒？有冇口爛、眼紅？皮膚一推有冇甩？」 |
| Meningococcal sepsis | Non-blanching purpuric rash + fever ± meningism [7] | 「啲紅點用杯壓落去係咪唔會消？」(Glass test) | |
| SLE | Malar rash sparing nasolabial folds, photosensitivity, arthralgia, oral ulcers [3] | 「面紅有冇避開鼻兩邊嗰條紋？曬太陽有冇差啲？」 | |
| Cutaneous malignancy | Changing mole/non-healing ulcer, asymmetry, border irregularity | 「有冇邊粒痣變大、變形、或者損咗唔好？」 | |
| Pitfalls | Scabies | Intense nocturnal itch, burrows at web spaces, close contacts affected | 「夜晚特別痕？手指罅有冇見到好細嘅線？屋企人有冇痕？」 |
| Tinea incognito | Rash worsened by steroids, atypical morphology [4] | 「搽類固醇之後反而差咗？」 | |
| Pityriasis rosea | Herald patch → Christmas tree distribution, self-limiting | 「第一粒紅疹係咪比其他大好多？背脊啲紅疹排列似聖誕樹？」 | |
| Secondary syphilis | Widespread MP rash involving palms/soles, condylomata lata | 「手板腳板有冇出紅疹？有冇新嘅性伴侶？」 | |
| Masquerades | Drug eruption | Temporal link to new drug, morbilliform, symmetric [5] | 「最近有冇食過新藥？食完幾耐出紅疹？」 |
| Diabetes-related skin changes | Acanthosis nigricans, necrobiosis lipoidica, recurrent candida | 「有冇糖尿病？頸後面有冇深色嘅皮膚？」 | |
| Thyroid disease | Pretibial myxoedema (Graves'), dry skin (hypothyroid) | 「有冇心跳快、手震、怕熱、或者好攰？」 | |
| Stress / anxiety / body image | Rash is the ticket; real concern is work stress, relationship, cosmetic | 「你最擔心紅疹邊方面呢？有冇影響你嘅心情或者人際關係？」 |
Skin Rash — Family Medicine Clinical Test Page
| Time | Task | Cantonese Key Phrases | Why It Scores Marks |
|---|---|---|---|
| 0:00–0:30 | Friendly opening, rapport, set agenda | 「你好呀，我係X醫生，今日由我幫你睇，可以點稱呼你呀？」「今日你嚟主要想睇啲咩呀？」 | Interpersonal marks: greeting, patient-centred opening |
| 0:30–2:00 | HPI: symptom analysis — site, onset, duration, progression, morphology, distribution, itch/pain, aggravating/relieving, treatments tried | 「呢個紅疹喺邊度先出㗎？」「出咗幾耐呀？」「有冇痕？定係痛呀？」「有冇搽過啲咩藥膏？有冇好轉過？」「有冇嘢令佢差啲或者好啲？例如曬太陽、出汗？」 | Core HPI marks; morphology + distribution → narrows DDx |
| 2:00–3:00 | Red flags + associated Sx — fever, weight loss, joint pain, mucosal ulcers, blisters, spreading rapidly, drug history | 「有冇發燒呀？」「有冇關節痛？」「有冇起水泡？」「最近有冇食過新藥或者抗生素？」「有冇口腔潰瘍？」 | Must-not-miss serious diagnoses (SJS/TEN, SLE, meningococcal) |
| 3:00–3:45 | PMHx, DHx, allergy, FHx, social Hx | 「你以前有冇濕疹、鼻敏感、哮喘呀？」「屋企人有冇類似嘅皮膚問題？」「你做咩工作呀？平時有冇接觸啲化學品？」「有冇食嘢敏感呀？」 | Atopic triad, contact exposure, drug allergy → DDx |
| 3:45–4:30 | ICE: uncover hidden agenda | 「你自己覺得呢個紅疹可能係咩呢？」(Idea)「你最擔心嘅係咩？」(Concern)「你今日嚟最希望我哋幫你做啲咩？」(Expectation) | ICE marks — biggest differentiator in scoring |
| 4:30–5:15 | Functional impact + psychosocial | 「呢個紅疹有冇影響你瞓覺呀？」「有冇影響你返工或者返學？」「你而家心情點呀？有冇因為佢覺得好煩躁或者唔開心？」 | Biopsychosocial marks; sleep disturbance is key in eczema |
| 5:15–6:00 | Summarise, signpost, safety-net, close | 「等我總結吓，你由X個星期前開始喺XX位出紅疹，主要係痕，你擔心…我聽得啱唔啱？」「我建議幫你檢查吓先。」「如果紅疹擴大、起水泡、或者發燒，要即刻返嚟或者去急症。」 | Summarising, checking understanding, safety-net → interpersonal marks |
Uncovering the hidden agenda: The patient may present with "rash" but the real RFC could be cosmetic worry, fear of cancer/contagion, impact on work/relationship, or medication side effects. Always ask 「你今日點解揀今日嚟睇呀？」 (Why did you come today specifically?) — this often reveals the trigger.
| Domain | English Question | Cantonese Question | Why It Matters | If Positive, Think Of |
|---|---|---|---|---|
| Site/Distribution | Where is the rash? Symmetrical? | 「紅疹喺邊度？兩邊都有定係得一邊？」 | Distribution is the single most important clue in dermatology [1] | Flexural = eczema; extensor = psoriasis; dermatomal = shingles; sun-exposed = SLE/drug |
| Onset/Duration | When did it start? Sudden or gradual? | 「幾時開始？突然定係慢慢出嚟？」 | Acute vs chronic narrows DDx dramatically | Acute + fever → viral exanthem, drug eruption; chronic relapsing → eczema, psoriasis |
| Morphology | What does it look like? Flat? Raised? Blisters? Scaly? | 「啲紅疹係平嘅定凸起嘅？有冇甩皮？有冇水泡？」 | Identify primary lesion: macule, papule, vesicle, plaque, pustule [2] | Vesicles = HSV/VZV/eczema herpeticum; silvery scale = psoriasis; honey crust = impetigo |
| Itch vs Pain | Itchy or painful? | 「痕定係痛呀？」 | Itch → eczema, urticaria, scabies; Pain → shingles, cellulitis, SJS | Painful rash + fever = red flag for SJS/TEN, NF |
| Aggravating/Relieving | Anything makes it worse? Heat, sun, soap, food? | 「有冇嘢令佢差啲？例如曬太陽、用梘液、食嘢？」 | Photosensitivity → SLE, drug eruption; soap → irritant dermatitis | Sun-aggravated → photosensitive lupus rash [3] |
| Treatments tried | Have you used any cream/medicine? Did it help? | 「搽過啲咩藥膏？有冇效？」 | Non-response to steroids → consider tinea (tinea incognito), or wrong diagnosis [4] | Steroid-worsened → tinea; no response → contact allergy to steroid itself |
| New drugs | Any new medications in last 1–2 months? | 「最近1-2個月有冇食過新藥？」 | Drug eruption onset: antibiotics within 1 week, anticonvulsants up to 2 months [5] | Morbilliform drug eruption, SJS/TEN, DRESS |
| Fever | Any fever? | 「有冇發燒呀？」 | Fever + rash = must-not-miss: meningococcal, SJS/TEN, viral exanthem | Non-blanching purpura + fever → meningococcal |
| Joint pain | Any joint pain or swelling? | 「有冇關節痛或者腫？」 | Rash + arthralgia → SLE, psoriatic arthritis, viral | Malar rash + arthralgia → SLE |
| Mucosal involvement | Any mouth ulcers, sore eyes, genital sores? | 「有冇口腔潰瘍、眼紅痛、或者下面損咗？」 | Mucosal involvement = key feature of SJS/TEN [5] | ≥2 mucosal sites + skin → SJS/TEN |
| Atopic history | Any history of eczema, asthma, allergic rhinitis? | 「你自己或者屋企人有冇濕疹、鼻敏感、哮喘？」 | Atopic triad — personal or FHx [1] | Atopic eczema |
| Contact/Occupation | What is your job? Contact with chemicals, metals, latex? | 「你做咩工㗎？有冇接觸化學品、金屬、手套？」 | Allergic contact dermatitis follows allergen exposure pattern [6] | Nickel (jewellery), latex (healthcare), cement (construction) |
| Sexual/STI Hx | Any new sexual partner? Genital rash? | 「有冇新嘅性伴侶？有冇下面出過紅疹？」 | Secondary syphilis, HIV seroconversion | Widespread MP rash + palms/soles + lymphadenopathy → secondary syphilis |
| Travel | Any recent travel? | 「最近有冇去過旅行？」 | Dengue, measles, chikungunya | Febrile rash post-travel → tropical infections |
| Functional impact | Does it affect sleep, work, mood? | 「有冇影響你瞓覺、返工、心情？」 | Biopsychosocial assessment | Sleep disturbance common in eczema/urticaria |
| Stress | Under any stress recently? | 「最近壓力大唔大？」 | Stress exacerbates eczema, psoriasis, urticaria | Psychosomatic component |
Case Report Form Answer Builder
Write: "[Age/Sex] with [duration] history of [skin rash description] over [distribution], associated with [itch/pain/fever/other], [aggravating/relieving factors], [treatments tried and response], [impact on function/sleep]."
Key HPI points to capture:
- Onset, duration, progression
- Site, distribution, symmetry
- Morphology of primary lesion [2]
- Itch vs pain
- Triggers/aggravating factors
- Prior treatments and response
- Associated systemic symptoms (fever, joint pain, mucosal Sx)
- Drug history with timing
- Atopic / FHx
- Functional impact
Examples:
- "Patient is concerned the rash may be contagious and wants a diagnosis"
- "Patient worried the rash may be serious (cancer/SLE) and wants reassurance"
- "Patient's itch is affecting sleep and daily function; wants effective treatment"
- "Patient noticed rash worsening despite OTC cream and wants proper management"
Tip: The RFC is NOT the symptom — it is WHY the patient came TODAY. Use the exact patient words from ICE.
| Likely Examples | How to Write | |
|---|---|---|
| Idea | "I think it might be eczema / fungal / allergy" | "Patient thinks the rash is due to allergy to a new detergent" |
| Concern | "I'm worried it's cancer / contagious / SLE / will scar" | "Patient is worried the rash may be skin cancer as a colleague was recently diagnosed" |
| Expectation | "I want a cream / blood test / referral to dermatologist" | "Patient expects a referral to a dermatologist for further assessment" |
Choose based on the stem's demographic + morphology + distribution + chronicity:
| Scenario | Most Likely Dx | Minimum Evidence |
|---|---|---|
| Chronic relapsing itchy rash, flexural, atopic FHx | Atopic eczema | Flexural distribution, personal/FHx atopy, ill-defined borders, chronic relapsing [1] |
| Well-demarcated silvery plaques, extensor, nail changes | Psoriasis | Extensor involvement, silvery scale, nail pitting, Auspitz sign [1] |
| Acute well-demarcated rash after contact exposure | Contact dermatitis | Well-demarcated border following exposure pattern, vesicles [6] |
| Transient wheals < 24h | Urticaria | Individual wheals resolve within 24h, dermatographism [1] |
| DDx | Key Discriminator |
|---|---|
| Psoriasis | Silvery scale, sharply demarcated, extensor, nail changes (vs eczema's ill-defined flexural pattern) [1] |
| Contact dermatitis | Well-demarcated distribution matching contact exposure; patch test confirmatory [6] |
| Tinea corporis | Annular with central clearing, KOH +ve; may worsen with steroids [4] |
| Drug eruption | Temporal relationship to new drug; symmetric morbilliform rash [5] |
| Scabies | Intense nocturnal itch, burrows, web spaces, household contacts affected |
| Pityriasis rosea | Herald patch, Christmas tree distribution on trunk, self-limiting |
(Pick the 3 most relevant to the stem given.)
| Domain | Example |
|---|---|
| Biological | Chronic itchy skin rash causing sleep disturbance and risk of secondary bacterial infection |
| Psychological | Anxiety about diagnosis / body image distress / low mood due to visible rash |
| Social/Functional | Impaired work/school performance due to itch/sleep loss; social embarrassment; need for time off |
| Diagnosis/DDx | Best Supporting Physical Sign | How to Elicit | Why It Supports This Diagnosis |
|---|---|---|---|
| Atopic eczema | Ill-defined erythematous plaques with lichenification at flexural sites + dry skin (xerosis) [1] | Inspect antecubital & popliteal fossae, neck, wrists; palpate for roughness/thickening | Flexural lichenification + xerosis is pathognomonic for chronic atopic eczema; atopic stigmata (Dennie-Morgan folds, palmar hyperlinearity) further support [8] |
| Psoriasis | Well-demarcated erythematous plaque with silvery scale on extensor surfaces; Auspitz sign (pinpoint bleeding on scale removal) [1] | Inspect elbows, knees, scalp, natal cleft; gently remove scale | Auspitz sign confirms psoriatic plaque; check nails for pitting |
| Contact dermatitis | Well-demarcated eczematous plaque conforming to area of allergen contact [6] | Inspect hands, wrists (watch strap), periorbital (cosmetics), feet (shoe) | Sharp demarcation + exposure pattern = contact dermatitis |
| Urticaria | Dermatographism (wheal after firm stroking of skin) [1] | Firmly stroke forearm skin with tongue depressor; observe for linear wheal within minutes | Positive dermatographism supports physical/chronic urticaria |
| Tinea corporis | Annular plaque with raised scaly active border and central clearing | Inspect trunk/limbs; KOH scraping of active edge | Ring-shaped + KOH +ve = dermatophyte infection |
| SJS/TEN | Nikolsky sign positive (epidermis slides with lateral pressure on erythematous skin) [5] | Apply gentle lateral pressure on erythematous area | Positive Nikolsky in febrile patient with mucosal erosions → SJS/TEN until proven otherwise |
| SLE | Malar (butterfly) rash sparing nasolabial folds [3] | Inspect face in good lighting | Sparing of nasolabial folds distinguishes SLE malar rash from rosacea |
| Scabies | Linear burrows at finger web spaces | Inspect finger web spaces, wrists with magnification | Burrows with nocturnal itch are pathognomonic |
Top Traps That Lose Marks
- Forgetting to ask about new medications — drug eruptions are common and frequently tested. Always ask timing: antibiotics within 1 week, anticonvulsants up to 2 months [5].
- Confusing eczema and psoriasis — Eczema = flexural, ill-defined, lichenification. Psoriasis = extensor, well-demarcated, silvery scale. Psoriasis involves extensor aspects with nail changes; eczema involves flexor surfaces [1].
- Missing tinea incognito — rash worsened by topical steroids that was previously treated as "eczema" [4]. Always ask about prior treatment response.
- Not asking about mucosal involvement — mucosal erosions (eyes, mouth, genitalia) = red flag for SJS/TEN [5].
- Forgetting ICE — many students describe the rash perfectly but score zero on ICE. Always ask all three explicitly.
- Not eliciting the RFC — the rash itself is not the RFC. The RFC is the patient's reason for coming today (e.g., fear, functional impact, specific request).
- Confusing malar rash (SLE) with rosacea — SLE spares nasolabial folds; rosacea involves them and has telangiectasia/papulopustules [3][6].
Must-Not-Miss Red Flags — Urgent Referral:
- Fever + painful widespread rash + mucosal involvement → SJS/TEN → A&E immediately [5]
- Non-blanching purpuric rash + fever → meningococcal sepsis → A&E immediately [7]
- Rapidly spreading painful erythema + fever + systemic toxicity → necrotising fasciitis → A&E
- New mole with ABCDE features → melanoma → urgent dermatology referral
- Malar rash + joint pain + oral ulcers → SLE → urgent medical referral [3]
Safety-Net Closing Line: 「如果紅疹擴大、起水泡、發燒、或者出現口腔潰瘍、眼痛，要即刻嚟急症室。」
High Yield Summary
What to ASK: Site/distribution, morphology, itch vs pain, onset/duration, new drugs (with timing), atopic/FHx, contact exposure, fever, mucosal symptoms, functional impact, ICE — especially the hidden agenda (Why today?).
What to WRITE: Clear HPI with morphology + distribution; ONE RFC reflecting the patient's concern; ICE with patient's own words; most likely diagnosis supported by distribution + morphology; 3 DDx each with one discriminator; biopsychosocial problems including sleep/mood/functional impact; one physical sign (e.g., flexural lichenification for eczema, silvery scale for psoriasis, Nikolsky sign for SJS/TEN).
What NOT to MISS: Drug eruption timing, SJS/TEN mucosal involvement, meningococcal purpura, tinea incognito (steroid-worsened rash), scabies in close contacts, SLE malar rash sparing nasolabial folds.
Active Recall - Family Medicine Clinical Test
[1] GC 065. I have an itchy rash.pdf (clinical features of atopic eczema, psoriasis, urticaria) [2] CFB (MED08) Dermatology (I).pdf; Dermatology I by Dr Chan.pdf (morphology of primary lesions, clinical cases) [3] GC 046. Facial rash and painful fingers_SLE.pdf; Block A - Facial rash and painful fingers_ SLE.pdf (malar rash, SLE cutaneous manifestations) [4] Dermatology I by Dr Chan.pdf p30–31 (tinea incognito clinical case, steroid non-response) [5] CFB (MED09) Dermatology (II).pdf p50, p53 (SJS/TEN clinical features, drug timing, Nikolsky sign, investigation) [6] Block A - Dermatology PBL 1.pdf p11 (contact dermatitis, chlorhexidine case); Ryan Ho Rheumatology.pdf p117 (allergic contact dermatitis) [7] Adrian Lui Pediatrics Notes.pdf p474 (meningococcal purpuric rash, glass test) [8] MBBS Final MB (Medicine) (Felix PY Lai).pdf p1786 (atopic eczema clinical features, atopic stigmata)
Skin Lesions (pigmented)
Pigmented skin lesions are areas of skin with altered coloration due to changes in melanin production, melanocyte proliferation, or vascular abnormalities, ranging from benign nevi and seborrheic keratoses to malignant melanoma.
Skin Ulcers
Skin ulcers are open lesions resulting from the loss of the epidermis and part or all of the dermis, often caused by vascular insufficiency, prolonged pressure, neuropathy, or infection, and characterized by impaired or delayed healing.