Why Dermatology Is Tested
Dermatology stations test candidates' ability to describe a skin lesion precisely and take a focused history. These are core skills relevant to every specialty — from general practice to surgery. Examiners use this station to assess descriptive vocabulary, systematic thinking, and the ability to formulate a sensible differential diagnosis.
💡 Tip
Dermatology is unusual in that description is itself the diagnosis in many cases. An accurate, structured description of a lesion should lead naturally to a differential. Practise out loud with dermatology atlases until lesion description becomes automatic.
Taking a Dermatology History
Presenting Complaint
- When did the rash/lesion first appear?
- Where did it start? Has it spread?
- Is it painful, itchy, burning, or asymptomatic?
- Is it getting better, worse, or static?
History of Presenting Complaint
- Speed of onset (sudden vs. gradual)
- Pattern over time (persistent, fluctuating, episodic)
- Any precipitating factor — sun exposure, new product, drug, food, stress, infection, heat
- Associated systemic symptoms — fever, joint pain, fatigue, weight loss, malaise
- Any similar episodes in the past
Drug History
- Current medications including OTC, herbal, supplements — many drugs cause rashes
- Any new drugs started in the past 2-3 months
- Topical treatments tried
Specific Dermatological Questions
| Question | Relevance |
|---|---|
| Any change in a pre-existing mole? | Melanoma — use ABCDE |
| Does anyone else at home have a similar rash? | Scabies, tinea (infectious) |
| Any known eczema, psoriasis, or skin conditions? | Flare of existing condition |
| Any family history of skin cancer or psoriasis? | Genetic predisposition |
| Sun exposure and sun protection habits? | Actinic keratosis, SCC, BCC, melanoma |
| Occupation and hobbies? | Contact dermatitis, agricultural exposures |
| Any immunosuppression (HIV, transplant, steroids)? | Atypical infections, Kaposi's sarcoma |
Social History
- Occupation (chemical exposures, outdoor work)
- Travel history (tropical infections, leishmaniasis)
- Smoking and alcohol
- Sexual history (secondary syphilis, HIV)
Describing a Skin Lesion — The Systematic Framework
Always describe lesions using the following framework:
1. Site and Distribution
- Anatomical location: face, trunk, limbs, palms, soles, flexures, extensor surfaces, mucous membranes
- Unilateral vs. bilateral; dermatomal vs. widespread
- Distribution pattern: photodistributed (SLE, PLE), flexural (eczema, intertrigo), extensor (psoriasis)
2. Number and Arrangement
- Solitary, multiple, grouped (herpetiform), linear, annular, dermatomal
3. Primary Lesion Type
| Term | Definition | Example |
|---|---|---|
| Macule | Flat colour change <1 cm | Freckle, café-au-lait |
| Patch | Flat colour change >1 cm | Vitiligo, Mongolian spot |
| Papule | Raised solid lesion <1 cm | Acne, molluscum |
| Plaque | Raised flat-topped lesion >1 cm | Psoriasis |
| Nodule | Solid raised lesion >1 cm, deeper | BCC, lipoma |
| Vesicle | Fluid-filled <1 cm | Herpes simplex, chickenpox |
| Bulla | Fluid-filled >1 cm | Bullous pemphigoid, second-degree burn |
| Pustule | Pus-filled | Acne, impetigo, folliculitis |
| Wheal | Transient raised oedematous | Urticaria |
| Telangiectasia | Dilated small blood vessels | Rosacea, hereditary haemorrhagic telangiectasia |
| Purpura | Non-blanching red/purple (blood outside vessels) | Meningococcaemia, HSP, ITP |
4. Secondary Changes
- Scale (psoriasis: silver scale; tinea: fine scale), crust (honey-coloured in impetigo), erosion (shallow), ulcer (deep), excoriation (scratch marks), lichenification (thickened skin with exaggerated skin markings), fissure, scar, atrophy, hyperpigmentation, hypopigmentation
5. Size
- Measure in cm (or describe as smaller than / similar to a coin)
6. Shape
- Round, oval, irregular, stellate, annular, serpiginous
7. Edge/Border
- Well-defined vs. poorly defined; raised edge (BCC — rolled, pearly edge); irregular vs. regular
8. Colour
- Erythematous, flesh-coloured, hyperpigmented, hypopigmented, violaceous, yellow (xanthoma), brown, black
9. Surface
- Smooth, rough, warty/verrucous, umbilicated (molluscum), crusted
10. Base
- On a stalk/pedunculated (skin tag), sessile
ABCDE of Melanoma
When describing a pigmented lesion, always apply the ABCDE criteria:
| Letter | Feature | Concerning Feature |
|---|---|---|
| A | Asymmetry | Asymmetrical shape |
| B | Border | Irregular, notched, or ill-defined border |
| C | Colour | Multiple colours within single lesion (brown, black, red, white, blue) |
| D | Diameter | >6 mm (though melanomas can be smaller) |
| E | Evolution | Any change in size, shape, colour, or symptoms |
⚠️ Red Flag
Any suspicious pigmented lesion with ABCDE features should be referred urgently under the NICE 2-week-wait pathway to a dermatologist. Do not reassure and discharge — document your findings and refer appropriately.
Common Conditions and Their Classic Descriptions
| Condition | Classic Description |
|---|---|
| Psoriasis | Well-defined erythematous plaques with silver-white scale on extensor surfaces (elbows, knees), scalp, and nails (pitting, onycholysis) |
| Eczema (atopic) | Poorly-defined erythematous patches with scaling and excoriation; flexural distribution (antecubital, popliteal fossae); lichenification if chronic |
| Basal cell carcinoma (BCC) | Pearly, flesh-coloured nodule with rolled telangiectatic edges; central ulceration in "rodent ulcer"; sun-exposed areas |
| Squamous cell carcinoma (SCC) | Hyperkeratotic, crusted, ulcerated nodule or plaque; sun-exposed areas; can arise from actinic keratosis |
| Melanoma | Pigmented lesion with ABCDE features; can be amelanotic |
| Tinea corporis | Annular, scaly, erythematous patch with central clearing; advancing edge |
| Herpes zoster (shingles) | Dermatomal distribution of grouped vesicles on erythematous base; unilateral; pain precedes rash |
| Impetigo | Honey-coloured crusted lesions on erythematous base; face/nares; highly contagious |
| Urticaria | Transient erythematous wheals; blanch on pressure; intensely pruritic |
| Cellulitis | Ill-defined erythema, warmth, swelling, tenderness; no raised edge; may have lymphangitis |
Dermoscopy and Skin Biopsy (for Discussion)
Be ready to discuss further investigation:
- Dermoscopy: magnification of pigmented lesions — used by dermatologists to assess for melanocytic features
- Punch biopsy / excision biopsy: histological diagnosis
- Skin swab: bacterial and viral cultures
- Wood's lamp: fluorescence in tinea capitis (green), erythrasma (coral-red), vitiligo (bright white)
- Patch testing: contact allergen identification
Common Mistakes
- Describing only the colour without other features
- Using "rash" or "spot" instead of specific terminology
- Forgetting to assess distribution
- Not examining the nails, scalp, hair, and mucous membranes
- Not applying ABCDE to pigmented lesions
- Failing to ask about occupational exposures and drug history
Examiner Tips and Mark Scheme Pointers
Mark schemes typically award points for:
- 1Systematic and complete lesion description using correct terminology
- 2Appropriate history taking including drug history, family history, and triggers
- 3ABCDE assessment of pigmented lesions
- 4Coherent differential diagnosis from description
- 5Appropriate investigation plan
- 6Safety-netting and referral if malignancy suspected
Frequently Asked Questions
"What is the ABCDE of melanoma and what features should prompt an urgent 2-week-wait referral?"
The ABCDE criteria for suspicious pigmented lesions are: Asymmetry, Border irregularity (notched or ill-defined), Colour variation within the lesion (multiple shades of brown, black, red, white, or blue), Diameter >6 mm, and Evolution (any change in size, shape, colour, symptoms, or bleeding). Any lesion with one or more of these features should be referred urgently via the NICE 2-week-wait pathway to a consultant dermatologist. In the OSCE, failing to mention the referral pathway after correctly identifying ABCDE features is a common reason marks are lost.
"What is the difference between a papule, a plaque, and a nodule?"
A papule is a raised, solid lesion less than 1 cm in diameter — examples include acne comedones and molluscum contagiosum. A plaque is a raised, flat-topped lesion greater than 1 cm — the classic example is psoriasis. A nodule is a solid raised lesion greater than 1 cm that extends deeper into the dermis or subcutaneous tissue — examples include basal cell carcinoma and lipoma. These distinctions are fundamental vocabulary that examiners expect you to use correctly — using "spot" or "lump" instead will lose you marks.
"How do you distinguish psoriasis from eczema on examination?"
Psoriasis produces well-defined, erythematous plaques with a characteristic silver-white scale on extensor surfaces (elbows, knees), the scalp, and the sacrum. Nail changes (pitting, onycholysis) and psoriatic arthritis are associated features. Atopic eczema produces poorly-defined, erythematous patches with scaling and excoriation in a flexural distribution (antecubital and popliteal fossae). In chronic eczema, lichenification (thickened skin with exaggerated skin markings from scratching) is a key feature. The distribution — extensor for psoriasis versus flexural for eczema — is the single most useful distinguishing feature.
"What questions are most important in the drug history for a dermatology OSCE?"
Ask specifically about: all current medications including OTC and herbal preparations; any new drugs started in the past 2-3 months (drug rashes can be delayed); topical treatments already tried and their effect; and any previous adverse drug reactions. Many drugs cause characteristic rashes — amoxicillin causes a maculopapular rash (especially in infectious mononucleosis), NSAIDs cause urticaria, and ACE inhibitors cause angioedema. Mentioning specific drug-rash associations demonstrates clinical depth and scores above average marks.
"What investigations would you request after describing a suspicious pigmented skin lesion?"
First, refer urgently to a dermatologist under the 2-week-wait pathway — this should be stated immediately. The dermatologist will perform dermoscopy (magnified examination of the pigmented lesion looking for melanocytic features) and, if indicated, excision biopsy with histopathological analysis to confirm the diagnosis. Punch biopsy is used for flat or inflammatory lesions. A skin swab is used if infection is suspected. A Wood's lamp may be used to assess for tinea capitis (green fluorescence), erythrasma (coral-red), or vitiligo (bright white) — these are recognised by examiners as showing breadth of dermatological knowledge.
"What areas of the body should never be omitted in a skin examination?"
A complete skin examination must include the nails (pitting, onycholysis in psoriasis; koilonychia in iron deficiency; clubbing in chronic disease), scalp (psoriasis, seborrhoeic dermatitis, alopecia), hair (alopecia areata, lichen planopilaris), mucous membranes (oral ulcers in Behcet's disease, Wickham's striae in lichen planus, Koplik's spots in measles), and the soles and palms (palmoplantar psoriasis, secondary syphilis, hand eczema). Omitting these areas is one of the most common mistakes in the dermatology OSCE mark scheme.
Related guides: Hip Examination OSCE · Explaining a Diagnosis OSCE · Musculoskeletal History OSCE · Safeguarding OSCE Guide