Seborrhoeic Dermatitis — SCE Dermatology MCQ
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Correct answer: E — Malassezia species
The correct answer is E, Malassezia species. Seborrhoeic dermatitis is a chronic inflammatory skin condition driven by an abnormal cutaneous inflammatory response to the lipophilic yeast Malassezia, which colonises sebum-rich (seborrhoeic) areas including the scalp, eyebrows, nasolabial folds and upper trunk. The well-defined erythematous patches with greasy yellow scale in exactly this distribution (nasolabial folds, eyebrows, scalp) in an otherwise well young adult is the classic clinical picture. Malassezia proliferates in sebaceous areas and its metabolites provoke an irritant and inflammatory response in susceptible individuals, producing the characteristic greasy scale rather than the fine silvery scale of psoriasis or dry scale of eczema. No skin swabs or scrapings are routinely needed as the diagnosis is clinical, and first line treatment is topical antifungal (ketoconazole) with or without mild topical corticosteroid. Why the other options are wrong: B. Trichophyton rubrum: This dermatophyte causes tinea (ringworm) with an active, often annular, spreading edge and central clearing, not symmetrical greasy scale confined to sebaceous sites. D. Staphylococcus aureus: Causes impetigo, folliculitis or cellulitis with pustules, crusting or frank infection signs, not chronic greasy scaling patches. A. Candida albicans: Produces intertriginous, moist, macerated erythema with satellite pustules in flexures, not dry sebaceous-area scaling. C. Propionibacterium acnes: Implicated in acne vulgaris pathogenesis (comedones, papules, pustules), which is a distinct clinical entity from the scaly patches described here. Key point: Greasy yellow scale in sebum-rich sites (scalp, eyebrows, nasolabial folds) is the hallmark of seborrhoeic dermatitis, caused by an inflammatory reaction to Malassezia yeast.
Reference: Patient.info Professional Reference (GP-authored, aligned with NICE CKS), Seborrhoeic Dermatitis, https://patient.info/doctor/seborrhoeic-dermatitis-pro