Free UKMLA dermatology questions with explanations

E. Stevens-Johnson syndrome

This presentation of widespread rash with oral and ocular mucosal ulceration two weeks after starting allopurinol is characteristic of Stevens-Johnson syndrome (SJS), a severe cutaneous adverse reaction with epidermal detachment of less than 10% body surface area and involvement of two or more mucosal sites. Allopurinol is among the most frequently implicated drugs in the UK, particularly in HLA-B*58:01 carriers, and requires immediate withdrawal plus specialist burns or dermatology input.

C. DRESS syndrome

DRESS (drug reaction with eosinophilia and systemic symptoms) typically appears 2-8 weeks after starting a culprit drug (commonly carbamazepine, phenytoin, lamotrigine, allopurinol or sulphonamides) and combines fever, morbilliform rash, facial oedema, lymphadenopathy, eosinophilia and organ involvement (most commonly hepatitis). Immediate drug withdrawal and supportive care, with systemic corticosteroids in severe cases, are the mainstays.

B. Concurrent sodium valproate therapy

Valproate inhibits the glucuronidation that clears lamotrigine, roughly doubling its half-life and plasma concentration at any given dose. Rapid rises in lamotrigine level early in treatment are the main driver of serious skin reactions, which is why the starting dose is halved to 25 mg on alternate days and titrated more slowly in anyone taking valproate. Starting at the usual 25 mg daily in a valproate-treated patient therefore exposes him to an effectively doubled dose. Atopy, sex, age and epilepsy syndrome do not materially alter the risk.

B. Topical permethrin 5% cream

The history of intense nocturnal pruritus, linear burrows in classic sites (finger webs, flexor wrists, genitals) and an affected household contact is diagnostic of scabies (Sarcoptes scabiei). Topical permethrin 5% cream is recommended as first-line, applied to the whole body, left on for 8 to 12 hours, and repeated after 7 days, with simultaneous treatment of all close contacts and laundering of clothing and bedding at 50°C or higher.

C. Septal panniculitis without vasculitis

Erythema nodosum is the prototypic septal panniculitis: inflammation is centred on the fibrous septa of the subcutaneous fat, with a mixed infiltrate and small granulomatous clusters (Miescher's radial granulomas) but no vasculitis and no fat necrosis, which is why the nodules do not ulcerate and heal without scarring. Lobular panniculitis with fat necrosis and vasculitis is the pattern of erythema induratum (nodular vasculitis), the main histological mimic, which affects the calves and ulcerates. Leukocytoclastic vasculitis produces palpable purpura rather than deep nodules, and a neutrophilic dermal infiltrate without vasculitis defines Sweet syndrome.

A. Topical ketoconazole 2% shampoo applied as a body wash

Pityriasis versicolor, caused by Malassezia yeasts (most often M. globosa), presents as hypopigmented or hyperpigmented finely scaling patches on the upper trunk, often more visible after sun-induced tanning, and fluoresces yellow-green under Wood's light. Topical ketoconazole shampoo or selenium sulfide is recommended as first-line; both are effective, but ketoconazole shampoo is generally better tolerated and easier to use as a short body wash regimen.

E. Potent topical corticosteroid

Localised cutaneous lichen planus is treated first with a potent or very potent topical corticosteroid, such as clobetasol propionate or betamethasone valerate 0.1%, applied to the papules until they flatten, with an emollient and a sedating antihistamine at night for the itch. The disease is self-limiting in most people within one to two years, so treatment aims at symptom control and limiting post-inflammatory hyperpigmentation. Systemic corticosteroids are held back for widespread, rapidly progressive, erosive or nail-destroying disease, and phototherapy or acitretin for extensive disease that fails topical treatment. Topical calcineurin inhibitors are used mainly for mucosal, genital or facial disease where long-term steroid use is undesirable.

C. Oral cetirizine

Urticaria is histamine-mediated, so a standard-dose second-generation non-sedating H1 antihistamine such as cetirizine is first-line and can be up-titrated to four times the licensed dose if symptoms persist. First-generation sedating antihistamines are avoided due to impaired cognition and sleep architecture. Escalation to omalizumab or ciclosporin is reserved for chronic refractory disease. Takeaway: Manage urticaria first-line with a non-sedating second-generation antihistamine, not a sedating one or systemic steroids.

D. Dermatofibroma

A dermatofibroma is a benign fibrous dermal nodule, most often on the lower legs of young to middle-aged adults, sometimes following minor trauma such as an insect bite. The lesion is firm and tethered to the overlying epidermis, so lateral pressure produces the characteristic dimple sign. It is harmless and is left alone unless symptomatic. The features that would raise concern for a nodular melanoma are rapid growth, irregular pigmentation, bleeding or ulceration, none of which is present.

D. Refer urgently under the suspected skin cancer pathway

Multiple rough scaly patches on chronically sun-exposed skin in an elderly outdoor worker are actinic keratoses, which are premalignant. Most are managed in primary care with field treatments or cryotherapy, but an actinic keratosis that becomes thickened, indurated, tender, rapidly enlarging or ulcerated has features of transformation to squamous cell carcinoma and must be referred urgently under the suspected skin cancer pathway. Induration and tenderness are the most useful warning signs because they suggest dermal invasion. Treating a possible SCC with topical field therapy or cryotherapy delays diagnosis.