UKMLA Dermatology Red Flags: High-Yield Revision Guide

Dermatology is the UKMLA specialty where half the marks are about recognising a killer rash in the first thirty seconds — and the other half are about de-escalating the obsessive use of topical steroids in a teenager with eczema. The GMC content map lists both red-flag emergencies (meningococcal septicaemia, SJS/TEN, necrotising fasciitis, erythroderma, anaphylaxis) and the chronic bread-and-butter (atopic eczema, psoriasis, acne vulgaris, skin cancer triage), and the AKT rewards candidates who can tell them apart at a glance.

This pillar covers every red-flag rash that must not be missed, the three types of skin cancer with their 2-week-wait referral triggers, eczema and psoriasis as NICE-aligned stepped therapies, acne vulgaris under NG198, common bacterial/fungal/viral skin infections, drug eruptions, and the topical steroid ladder with finger-tip-unit dosing. We close with a pattern library — the twelve stems that dominate UKMLA dermatology.

Use this alongside our emergency presentations masterclass for meningococcal septicaemia and anaphylaxis, the paediatrics high-yield guide for paediatric rash differentials, the infectious diseases guide for cellulitis and nec fasc overlap, and NICE guidelines high-yield for the stepped-therapy principles the AKT expects.

1. Why Dermatology SBAs Hinge on Recognition

Dermatology is pattern-matching medicine. The UKMLA stem will rarely ask you to biopsy — it will ask you to recognise the rash, decide on urgency, and pick the first-line management.

The stems fall into four buckets:

1. Emergencies — the rash that kills in hours (meningococcal, SJS/TEN, nec fasc, anaphylaxis, erythroderma).
2. Cancer triage — the lesion that needs a 2WW referral (melanoma, SCC).
3. Chronic inflammatory — eczema, psoriasis, acne with NICE stepped therapy.
4. Infections and drug reactions — cellulitis, impetigo, fungal, viral exanthems, drug rashes.

The three habits that raise a dermatology score: (1) always describe the rash systematically — distribution, morphology (macule/papule/vesicle/pustule/plaque/nodule/ulcer), colour, secondary features (scale, crust, excoriation, lichenification); (2) always ask which features make it a red flag — fever, mucosal involvement, skin pain, new rapidly progressing pigmented lesion; (3) always remember the drug history — most inpatient rashes are iatrogenic.

2. Meningococcal Rash — Recognition and Immediate Action

Meningococcal septicaemia is the classic "miss this and the patient dies within hours" rash. The GMC mark it as a must-recognise red flag for every UK medical graduate.

Clinical features:

• Fever, headache, neck stiffness, photophobia (meningitic features) or shock without meningitis (septicaemic).
• Non-blanching petechial or purpuric rash — does not fade on pressure (glass test or tumbler test).
• Starts as small petechiae (pinpoint, peripheral), progresses to purpura (larger, stellate), then purpura fulminans (widespread necrotic skin).
• Cold peripheries, mottling, delayed capillary refill — distinguishes septicaemic presentation.

Differential for non-blanching rash:

• Meningococcal septicaemia (must assume until excluded)
• Other sepsis with DIC (pneumococcal, gram-negative, staphylococcal)
• ITP, leukaemia, HUS (context-dependent)
• Henoch-Schönlein purpura (IgA vasculitis — palpable purpura on buttocks and legs in children — see paediatrics guide)
• Trauma (linear patterns)

Immediate management (pre-hospital or ED):

• IM/IV benzylpenicillin before transfer if primary care — 1.2 g adult / 600 mg 1–9 years / 300 mg <1 year.
• In ED: IV ceftriaxone 2 g (add amoxicillin in over-50s to cover Listeria; see infectious diseases guide).
• Resuscitate with IV fluids, oxygen, monitor, ICU if shock.
• Public Health England notification is mandatory.
• Prophylaxis for close contacts: ciprofloxacin single dose (or rifampicin).

UKMLA trap: a feverish child with a single petechial spot in a "non-blanching rash" — even a single petechiae warrants urgent assessment and empirical antibiotics.

3. SJS / TEN — Triggers, Management, Mortality

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are a spectrum of severe mucocutaneous drug reactions. Classification by body surface area (BSA) detached:

• SJS: <10%
• SJS/TEN overlap: 10–30%
• TEN: >30%

Pathophysiology: CD8+ T-cell-mediated keratinocyte apoptosis triggered by drug or metabolite. Mortality 10% SJS, up to 50% TEN.

Common drug triggers (HLA-associated in some populations):

• Anticonvulsants: carbamazepine, lamotrigine, phenytoin, phenobarbital
• Allopurinol (HLA-B*5801 in Han Chinese — screen before starting)
• Sulphonamides (co-trimoxazole)
• NSAIDs (especially oxicams)
• Nevirapine
• Sulfasalazine, dapsone

Clinical features:

• Prodrome (1–14 days after drug start): fever, malaise, myalgia.
• Mucocutaneous phase: painful erythematous rash on trunk/face progressing to flaccid bullae and epidermal detachment.
• Nikolsky sign positive — lateral pressure slides skin off underlying tissue.
• Mucosal involvement (≥2 sites): oral, ocular, genital — key discriminator from erythema multiforme.
• Systemic: fever, tachycardia, hypotension, hepatitis, AKI, pneumonitis.

Management:

• Stop the culprit drug immediately (the single most important action — each day of continued exposure worsens outcome).
• Transfer to specialist burns unit or ICU.
• Supportive: aggressive fluid resuscitation (20–30% BSA loss → burn-level crystalloid), analgesia (often opioids), temperature regulation, nutrition (enteral feeding), wound care (non-adherent dressings, silver sulfadiazine).
• Ophthalmology review daily (adhesions, scarring risk for blindness).
• SCORTEN score predicts mortality (age, malignancy, HR, BSA, urea, bicarbonate, glucose).
• Adjuncts: IVIG, ciclosporin, infliximab — evidence limited, guided by specialist.

UKMLA trap: a patient on lamotrigine with rash + oral ulcers + conjunctivitis + fever → SJS → stop lamotrigine, admit, supportive care. Do not "rechallenge."

4. Necrotising Fasciitis — LRINEC, Surgical Timing

Necrotising fasciitis is rapidly progressive soft tissue infection of fascia and muscle with systemic toxicity. Mortality 20–40%.

Types:

• Type I: polymicrobial (anaerobes + gram negatives + streptococci) — diabetes, post-surgical, IVDU.
• Type II: Streptococcus pyogenes (group A strep, often invasive) — healthy hosts, rapid progression, toxic shock syndrome.
• Type III: Vibrio vulnificus (seawater/raw seafood), Clostridium perfringens (gas gangrene).
• Type IV: fungal (rare, immunocompromised).

Clinical features:

• Pain out of proportion to physical signs — cardinal feature, often before visible skin changes.
• Erythema progresses to dusky/grey skin, tense oedema, blisters, bullae, crepitus (gas in tissue), necrotic skin patches.
• Systemic toxicity: fever, tachycardia, hypotension, confusion.
• Fournier's gangrene: perineal/scrotal nec fasc.

LRINEC score (Laboratory Risk Indicator for Necrotising Fasciitis): CRP, WCC, Hb, Na, Cr, glucose. Score ≥6 = high suspicion (but DO NOT rely on it — clinical suspicion is paramount).

Investigation:

• Bedside: clinical examination; "finger test" (dissection without resistance under local anaesthesia).
• CT/MRI: fascial oedema, gas — but do not delay surgery for imaging.

Management:

• Immediate surgical debridement (within hours — most important determinant of survival).
• IV broad-spectrum antibiotics (piperacillin-tazobactam + clindamycin for toxin suppression + vancomycin if MRSA risk).
• Fluid resuscitation, ICU.
• IVIG for strep toxic shock (evidence modest).
• Serial debridement every 24 hours until clean.
• Amputation if limb non-salvageable.

UKMLA trap: a diabetic with "cellulitis" that is not responding to antibiotics, with severe pain and a tense area + gas on X-ray → nec fasc → immediate surgery, not longer antibiotics.

5. Skin Cancer Triage: BCC vs SCC vs Melanoma

UK skin cancer incidence has been rising for two decades. The UKMLA tests the triage: which lesion is benign, which needs watching, which needs a 2-week-wait referral.

Basal cell carcinoma (BCC):

• Commonest skin cancer. Slow-growing, locally destructive, almost never metastasises.
• Subtypes: nodular (classic pearly papule with telangiectasia, rolled edge, central ulceration — "rodent ulcer"), superficial (erythematous scaly patch), morphoeic (ill-defined scar-like plaque, harder to excise), pigmented.
• Sun-exposed areas (face, ears, scalp, back).
• Management: surgical excision (standard), Mohs for high-risk sites (central face, nasolabial fold, periorbital), cryotherapy or imiquimod for superficial BCC, radiotherapy if surgery declined.
• Referral: routine dermatology referral (not 2WW, unless concerning features or diagnostic uncertainty).

Squamous cell carcinoma (SCC):

• Second commonest. Can metastasise (especially on lip, ear, immunosuppressed).
• Actinic keratosis → Bowen's (SCC in situ) → invasive SCC (escalation).
• Features: scaly, crusted, indurated lesion, may ulcerate. Sun-exposed sites. Fast-growing in weeks to months.
• 2-week-wait referral (NICE NG12) for suspected SCC (non-healing, indurated, bleeding, rapidly growing lesion).
• Management: surgical excision with margins; Mohs for high-risk sites; radiotherapy, chemotherapy for advanced.

Malignant melanoma:

• Lifetime UK risk ~1 in 36 men, 1 in 47 women and rising. Highest mortality of skin cancers.
• Subtypes: superficial spreading (commonest), nodular (worst prognosis — vertical growth early), lentigo maligna (elderly, sun-damaged face), acral lentiginous (palms/soles/nails, darker skin types).
• 2-week-wait referral if suspected.
• Management: wide local excision (margins based on Breslow thickness), sentinel lymph node biopsy if Breslow >1 mm, adjuvant immunotherapy (ipilimumab, nivolumab, pembrolizumab) or targeted therapy (BRAF/MEK inhibitors if BRAF+) for advanced.

Prognosis (Breslow thickness):

• <1 mm: ~95% 5-year survival.
• 1–2 mm: 80–90%.
• 2–4 mm: 60–70%.

• 4 mm: 40–50%.

6. ABCDE of Melanoma + 2-Week-Wait Referral

ABCDE criteria for suspicious pigmented lesions:

• Asymmetry
• Border (irregular, notched)
• Colour (variegated — 2+ colours)
• Diameter >6 mm (not absolute — small melanomas exist)
• Evolution (change over weeks/months — size, shape, colour, bleeding, itching, ulceration)

7-point checklist (Weighted Glasgow) — alternative used in UK primary care:

• Major (2 points each): change in size, change in shape, change in colour.
• Minor (1 point each): inflammation, oozing/bleeding, sensory change, diameter ≥7 mm.
• Score ≥3 → 2WW referral.

NICE NG12 criteria for suspected melanoma 2WW:

• Weighted 7-point checklist ≥3 or
• Dermoscopy suggests melanoma or
• New or changing pigmented lesion with other red flags.

Subungual melanoma clue: Hutchinson's sign (pigmentation extending to nail fold) is suggestive. Subungual melanoma often mistaken for haematoma — if no history of trauma and no clear resolution, refer.

UKMLA trap: an evolving pigmented lesion with ABCDE features or a 7-point score ≥3 → 2WW referral (not "apply 5-FU cream and review").

7. Eczema — Atopic, Contact, Management Ladder

Atopic eczema (AD) is chronic relapsing inflammatory dermatosis with itch, redness, scaling, and lichenification. Associated with atopic triad (eczema, asthma, hay fever).

Distribution by age:

• Infants: cheeks, extensor surfaces, trunk.
• Children/adults: flexural (antecubital, popliteal), neck, eyelids, hands.

Triggers: allergens (dust mites, pets, pollen), irritants (soaps, detergents, wool), infection (S. aureus, HSV — eczema herpeticum), stress, heat, sweat, food (children, minority).

Management (NICE NG247 + CG57 for children):

• Stepped by severity:
  • Mild: emollients + mild topical steroid (hydrocortisone 1%).
  • Moderate: emollients + moderate-potency steroid (betamethasone valerate 0.025%, clobetasone butyrate 0.05%).
  • Severe: emollients + potent steroid (betamethasone valerate 0.1%, mometasone) or very potent (clobetasol propionate) short-term.
• Emollients constantly — ≥250 g/week in adults; thicker ointments for night, creams for day. Apply in direction of hair growth.
• Topical calcineurin inhibitors (tacrolimus, pimecrolimus) for face, eyelids, flexures (steroid-sparing).
• Wet wraps for severe eczema.
• Antihistamines for sleep (sedating, short-term).
• Bandages (zinc paste, ichthammol) for lichenified areas.
• Phototherapy (UVB) for extensive disease.
• Systemic: ciclosporin, methotrexate, azathioprine, dupilumab (IL-4/13, biologic).

Eczema herpeticum: HSV superinfection — monomorphic punched-out vesicles, fever, systemic illness. Emergency — IV aciclovir, ophthalmology review if near eyes.

Contact dermatitis:

• Irritant (commonest): direct damage (detergents, solvents). Any age, confined to contact area.
• Allergic (type IV hypersensitivity): e.g. nickel (earrings, belt buckles), fragrances, rubber. Patch testing.
• Management: identify and avoid trigger, emollients, topical steroids as above.

UKMLA trap: child with eczema develops monomorphic vesicles and fever → eczema herpeticum → IV aciclovir.

8. Psoriasis — Types, NICE-Aligned Stepped Therapy

Psoriasis is chronic immune-mediated hyperproliferation of keratinocytes with plaques, scaling, and sometimes arthritis. Prevalence 2%.

Types:

• Chronic plaque (90%): well-demarcated erythematous plaques with silvery scale, extensors (elbows, knees), scalp, sacrum. Auspitz sign (pinpoint bleeding after scale removal).
• Guttate: sudden eruption of small drop-like papules in young adults, often post-streptococcal throat infection.
• Flexural (inverse): smooth red plaques in flexures/groin/axilla.
• Pustular: sterile pustules; may be generalised (von Zumbusch) — medical emergency.
• Erythrodermic: >90% BSA erythema — emergency (sepsis risk, temperature dysregulation, cardiac failure).
• Nail: pitting, onycholysis, subungual hyperkeratosis, oil-drop sign.
• Psoriatic arthritis: 10–30% — see MSK guide.

Triggers: streptococcal infection (especially guttate), stress, alcohol, smoking, drugs (β-blockers, lithium, antimalarials, NSAIDs, withdrawal of steroids), Koebner phenomenon (lesions at sites of trauma).

Management (NICE CG153):

• Step 1 — topical:
  • Chronic plaque: emollients + potent topical steroid OD + vitamin D analogue OD (calcipotriol, calcitriol) for up to 4 weeks.
  • Scalp: topical steroid lotion/gel + vitamin D analogue.
  • Face/flexural: mild steroid only (short term).
• Step 2 — phototherapy: narrow-band UVB for extensive disease.
• Step 3 — systemic: methotrexate first-line, ciclosporin (short-term), acitretin.
• Step 4 — biologics: anti-TNF (adalimumab, etanercept), anti-IL12/23 (ustekinumab), anti-IL17 (secukinumab, ixekizumab), anti-IL23 (guselkumab, risankizumab). Use if severe and failed other therapy.
• Generalised pustular / erythrodermic: admit, IV fluids, temperature regulation, systemic therapy urgently.

UKMLA trap: child with recent sore throat develops small drop-like lesions → guttate psoriasis → topical steroid + vitamin D analogue; often self-limiting over weeks.

9. Acne Vulgaris — NICE Stepped Management

Acne is very common in adolescence. NICE NG198 (2023) standardises treatment.

Classification:

• Mild: predominantly comedones (open/closed), few inflammatory lesions.
• Moderate: more inflammatory papules and pustules, few nodules.
• Severe: nodules, cysts, scarring, widespread.

Management (NICE NG198):

• Mild to moderate:
  • First-line: a 12-week course of one of:
    • Topical adapalene + benzoyl peroxide (fixed combination).
    • Topical tretinoin + clindamycin (fixed combination).
    • Topical benzoyl peroxide + clindamycin (fixed combination).
    • Topical azelaic acid + oral lymecycline or doxycycline.
  • Avoid monotherapy with oral or topical antibiotics (resistance).
• Moderate to severe or failed topical:
  • Oral antibiotic (lymecycline 408 mg OD or doxycycline 100 mg OD) + topical adapalene/BPO — 12 weeks, max 6 months.
  • Combined oral contraceptive in women as alternative systemic therapy (co-cyprindiol for moderate-severe).
• Severe, resistant, scarring:
  • Referral to dermatology for oral isotretinoin — highly effective; requires pregnancy prevention programme (Roaccutane is teratogenic, monthly pregnancy tests, two forms of contraception, one month before and after). Side effects: mucocutaneous (dry skin/lips), hepatic, hyperlipidaemia, mood (rare but important), IIH (avoid tetracyclines with isotretinoin).
• Treat acne scarring after active disease controlled.

UKMLA traps:

• Never use oral or topical antibiotic alone (resistance risk).
• Severe nodulocystic acne with scarring → refer for isotretinoin.
• Doxycycline + isotretinoin → risk of IIH (pseudotumour cerebri) → do NOT co-prescribe.

10. Cellulitis vs Erysipelas vs Necrotising

Cellulitis management (UK — NICE NG141 cellulitis/Eron classification):

• Class I (no systemic illness, no comorbidity) — oral flucloxacillin 500 mg QDS 5–7 days. Clarithromycin if penicillin-allergic.
• Class II (systemic features but no unstable comorbidity) — admit for IV flucloxacillin or treat in ambulatory unit.
• Class III (significant systemic features or unstable comorbidity) — admit for IV flucloxacillin + consider broader cover.
• Class IV (sepsis or life-threatening) — ICU, IV broad-spectrum.
• Mark the area of erythema with a pen to track progression.
• Elevate limb.
• Look for and treat portal of entry (tinea pedis, leg ulcer, eczema).

Diabetic foot infection:

• Risk of osteomyelitis (probe to bone test).
• Broader cover (co-amoxiclav, or piperacillin-tazobactam if moderate-severe).
• MDT: diabetes team, podiatry, orthopaedics, vascular.

SBA traps:

• Cellulitis not responding to oral flucloxacillin and a tense shiny area with severe pain → consider necrotising fasciitis → surgery.
• Chronic lower leg "cellulitis" that fluctuates with elevation → often venous eczema, not infection — treat with elevation + emollients + compression.

11. Impetigo and Other Bacterial Skin Infections

Impetigo:

• Commonest in children. Caused by S. aureus (bullous) or group A strep (non-bullous, "honey-crusted").
• Highly contagious.
• Management (NICE NG153):
  • Localised non-bullous: topical hydrogen peroxide 1% cream first-line; topical fusidic acid 2% or mupirocin if hydrogen peroxide unsuitable/unsuccessful (avoid in extensive disease to reduce resistance).
  • Widespread/bullous/systemic: oral flucloxacillin (clarithromycin if allergic).
  • Off school until lesions crusted or 48 hours after starting antibiotics.

Folliculitis, furuncle (boil), carbuncle:

• Inflammation of hair follicles (S. aureus).
• Management: warm compresses, incision and drainage for pus, topical or oral antibiotics if extensive.

Erythrasma:

• Corynebacterium minutissimum. Brown scaly plaques in skin folds (groin, axilla). Coral-red fluorescence on Wood's lamp.
• Management: topical fusidic acid or oral erythromycin.

Scabies:

• Sarcoptes scabiei. Intensely itchy, especially at night; burrows on wrists, finger webs, genitals; pruritus for weeks after treatment.
• Management: permethrin 5% cream, full body application, leave 8–12 hours, repeat 1 week later. Treat all household contacts simultaneously. Wash bedding at 60°C.

Head lice:

• Wet combing with conditioner every 4 days for 2 weeks first-line. Dimeticone 4% lotion if combing fails.

12. Fungal Infections (Tinea, Candida)

Dermatophyte (tinea) infections:

• Tinea capitis (scalp): children, broken hairs, scale, may progress to kerion (boggy inflammatory mass). Management: oral griseofulvin or terbinafine (topical insufficient).
• Tinea corporis (body): annular scaling plaque with central clearing and raised edge. Topical clotrimazole/terbinafine.
• Tinea pedis (athlete's foot): interdigital scaling, itch. Topical antifungal.
• Tinea cruris (groin): scaly edge, often from tinea pedis. Topical antifungal.
• Tinea unguium / onychomycosis (nail): thick, discoloured, crumbly nail. Oral terbinafine 3 months (fingernails) or 6 months (toenails) after confirming fungus on nail clippings.

Candida:

• Oral thrush: white plaques on buccal mucosa, tongue. Nystatin suspension or oral fluconazole. Check for immunocompromise (HIV, diabetes, steroid inhaler).
• Vaginal thrush: pruritus, cheesy discharge. Clotrimazole pessary or oral fluconazole 150 mg single dose.
• Intertrigo (skin fold candidiasis): erythema, satellite lesions, beefy red. Keep area dry; topical clotrimazole or nystatin.

Pityriasis versicolor:

• Malassezia furfur. Hypo- or hyper-pigmented patches on trunk, young adults, more visible after tanning. Fine scale. Management: topical ketoconazole shampoo, selenium sulphide, oral itraconazole for extensive disease.

UKMLA trap: child with patch of alopecia + scale + broken hairs → tinea capitis → oral antifungal (topical insufficient) plus mycology nail clippings / skin scrapings.

13. Viral Exanthems (Shingles, HSV)

Herpes zoster (shingles):

• Reactivation of VZV along a dermatome. Unilateral, pain often precedes rash, vesicles on erythematous base, crust over 7–10 days.
• Complications: postherpetic neuralgia (pain >3 months), ophthalmic zoster (V1 — Hutchinson's sign: tip-of-nose involvement = nasociliary nerve → eye involvement — urgent ophthalmology), Ramsay Hunt (VII + VIII — facial palsy + ear vesicles + vertigo + hearing loss).
• Antivirals within 72 hours of rash onset: aciclovir 800 mg 5× daily for 7 days; valaciclovir / famciclovir are alternatives with better compliance.
• Ophthalmic zoster → oral + ophthalmology referral.
• Pregnant women with chickenpox contact → VZV IgG, VZIG if non-immune.
• Shingles vaccine (Shingrix) recommended age 65+ and immunocompromised.

Herpes simplex (HSV):

• HSV-1: predominantly orolabial ("cold sores").
• HSV-2: predominantly genital.
• Primary infection: painful vesicles, systemic features. Recurrence milder.
• Management: topical aciclovir for mild; oral aciclovir 200 mg 5× daily for 5 days for moderate-severe; suppressive therapy for frequent recurrence.

Molluscum contagiosum: poxvirus, pearly umbilicated papules, children and immunocompromised. Self-limiting in 6–18 months; cryotherapy/curettage if troublesome.

Warts: HPV. Topical salicylic acid + cryotherapy.

Hand, foot and mouth disease: coxsackie A16 / enterovirus 71. Fever + vesicles on hands/feet + oral ulcers. Self-limiting.

14. Drug Rashes and Fixed Drug Eruptions

Morbilliform (maculopapular) drug eruption:

• Commonest drug rash. Diffuse erythematous macules and papules, itching, trunk and limbs, begins 5–14 days after drug start.
• Common culprits: penicillins, cephalosporins, anticonvulsants, allopurinol, NSAIDs.
• Management: stop the drug (unless essential), antihistamines, emollients, mild topical steroid.

Fixed drug eruption:

• Well-demarcated, round, erythematous/dusky plaque that recurs in the same location each time the drug is given.
• Common culprits: tetracyclines, sulphonamides, NSAIDs, paracetamol.

Urticaria:

• Wheals with itch, lasting <24 hours individual lesions. Acute <6 weeks, chronic >6 weeks. Non-sedating antihistamine first-line.

Angioedema:

• Deeper swelling of dermis and subcutaneous tissue. Can be allergic (IgE-mediated — with urticaria) or non-allergic (ACEi-induced, HAE). Airway threat → adrenaline (for anaphylaxis), C1-esterase inhibitor for HAE.

DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms):

• Rash + fever + lymphadenopathy + eosinophilia + organ involvement (hepatitis, pneumonitis, carditis, nephritis). Onset 2–8 weeks after drug.
• Culprits: anticonvulsants (carbamazepine, phenytoin), allopurinol, minocycline, sulphonamides.
• Management: stop drug, systemic steroids, supportive.

Erythema multiforme:

• Target lesions (three concentric rings), acral distribution, usually HSV-triggered; less commonly drug-triggered. Self-limiting if minor; consider SJS if severe with mucosal involvement.

SBA trap: 2 weeks after starting carbamazepine, a patient has rash + fever + lymphadenopathy + elevated ALT + eosinophilia → DRESS → stop carbamazepine + systemic steroids.

15. Topical Steroid Ladder and Safe Use

Topical steroid potency and site selection matter for UKMLA.

UK potency ladder (low → very high):

Finger-tip unit (FTU): amount of cream/ointment squeezed from a standard tube from tip to first crease — ~0.5 g, covers 2 hand prints of body surface.

FTU guidance:

• Face/neck: 2.5 FTU
• Whole arm: 3–4 FTU
• Whole leg: 6 FTU
• Torso front: 7 FTU
• Torso back + buttocks: 7 FTU

Safe use principles:

• Use lowest potency effective.
• Avoid potent/very potent on face, flexures, genitalia unless specialist-directed.
• Apply thinly once or twice daily.
• Do not apply immediately before or after emollient — leave 20 minutes; steroid first on active lesion, then emollient elsewhere.
• Taper: step down potency as disease improves; break courses.
• Review if need to use potent steroid >2 weeks on face, >4 weeks on body, >8 weeks on palms/soles.

Side effects (especially with prolonged potent use):

• Skin thinning (atrophy), striae, telangiectasia.
• Perioral dermatitis (face).
• Periocular glaucoma, cataract.
• Tachyphylaxis (loss of response).
• Systemic absorption (HPA axis suppression in children, large BSA, prolonged use).
• Topical steroid withdrawal (increasingly recognised — pruritus, erythema, flaking after stopping prolonged potent use).

UKMLA trap: mother applying clobetasol to a toddler's face — counsel against very potent steroids on face; step down to hydrocortisone 1%, consider tacrolimus for flexural/facial maintenance.

The UKMLA Dermatology Pattern Library

Twelve stems worth owning:

1. Feverish child with non-blanching rash → meningococcal septicaemia → IM benzylpenicillin + transfer.
2. Rash + oral ulcers + conjunctivitis on lamotrigine → SJS → stop drug, burns unit.
3. Diabetic with pain-out-of-proportion + dusky skin + gas → necrotising fasciitis → surgery now.
4. Evolving pigmented lesion, asymmetric, 8 mm, changing colour → melanoma → 2WW.
5. Non-healing indurated crusty lesion on lip in smoker → SCC → 2WW.
6. Pearly nodule with telangiectasia on nose → BCC → routine dermatology referral.
7. Silvery scaly plaques on elbows + nail pitting → chronic plaque psoriasis → topical steroid + vitamin D analogue.
8. Child with eczema + punched-out monomorphic vesicles + fever → eczema herpeticum → IV aciclovir.
9. Adolescent with moderate acne → fixed combination topical (adapalene + BPO + clindamycin) ± lymecycline; avoid monotherapy antibiotics.
10. Oral + facial vesicles along a dermatome, with tip-of-nose involvement → ophthalmic zoster → oral aciclovir + ophthalmology.
11. Tense boggy scalp lesion with broken hairs in a child → tinea capitis (kerion) → oral terbinafine / griseofulvin.
12. Rash + fever + lymphadenopathy + eosinophilia + hepatitis 4 weeks into carbamazepine → DRESS → stop drug, systemic steroids.

Putting It All Together

Dermatology rewards a four-track memory: red flags (meningococcal, SJS/TEN, nec fasc, anaphylaxis, erythroderma), cancer triage (BCC / SCC / melanoma with 2WW triggers), chronic inflammatory stepped therapy (eczema, psoriasis, acne), and infections/drug reactions. Every UKMLA dermatology SBA fits one of those tracks — the key is to triage the rash to the right track within seconds.

Pair this pillar with our emergency presentations masterclass for the meningococcal, anaphylaxis, and SJS/TEN algorithms, the paediatrics high-yield guide for paediatric-specific rashes (HSP, measles, HFMD, scarlet fever), the infectious diseases guide for cellulitis and LRINEC, and NICE guidelines high-yield for the stepped-therapy pattern the AKT expects.

If a rash stem reads ambiguously, the fastest way to sort it is to ask: is this emergency, cancer, chronic, or infection/drug? Ninety per cent of UKMLA dermatology sits in one of those four buckets. Ready to test yourself? Start with an MLA Prep dermatology mini-mock and see which of the twelve patterns you close on first read.