Paraneoplastic Dermatosis — SCE Dermatology MCQ

Correct answer: B — Underlying malignancy (especially lung carcinoma) — present in >80% of cases

The correct answer is B, underlying malignancy (especially lung carcinoma), present in over 80% of cases. Erythema gyratum repens (EGR) is a paraneoplastic figurate erythema, and the rapidly migrating (up to 1 cm/day), concentric wood-grain banding described in the stem is the classic morphological clue that should immediately trigger a search for an occult tumour. Bronchial carcinoma is the single most common underlying cancer, though oesophageal, breast, gastric and other malignancies are also reported. Because the eruption frequently precedes the cancer diagnosis by weeks to months, any patient presenting with this pattern requires urgent, comprehensive malignancy screening (chest imaging as a priority, plus age-appropriate cancer work-up). The rash typically regresses once the underlying tumour is treated, reinforcing the causal paraneoplastic link. Why the other options are wrong: A. Tinea corporis: dermatophyte infection causes slowly enlarging, scaly annular plaques with central clearing and an active advancing edge, not rapidly migrating concentric wood-grain bands, and skin scrapings would be positive for fungal elements, which is not the discriminating feature here. D. Sarcoidosis: sarcoid skin disease produces papules, plaques or erythema nodosum, not a rapidly migrating figurate wood-grain pattern, and is not the recognised association for EGR. E. Pregnancy: pregnancy is linked with polymorphic eruption of pregnancy and pemphigoid gestationis, neither of which resembles the wood-grain morphology of EGR. C. Drug reaction: drug eruptions typically present as morbilliform, urticarial or fixed patterns rather than the specific concentric, rapidly migrating gyrate banding described, and drugs are not the recognised cause of true EGR. Key point: Erythema gyratum repens with its wood-grain, rapidly migrating morphology is one of the strongest cutaneous markers of internal malignancy and mandates urgent screening, particularly for lung cancer.

Reference: DermNet NZ, Erythema gyratum repens, 2019, https://dermnetnz.org/topics/erythema-gyratum-repens