Pityriasis versicolor — DTM&H MCQ

Instant feedback + full explanation. One question, done properly.

EasyDermatological Tropical ConditionsPityriasis versicolorDTM&H

A 20-year-old man in tropical Brazil presents with multiple hypopigmented macules on his trunk and upper arms that do not tan with sun exposure. Skin scrapings with KOH preparation show short hyphae and round yeast cells ('spaghetti and meatballs' appearance). What is the most likely diagnosis?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Pityriasis versicolor

The correct answer is E, Pityriasis versicolor. This superficial fungal infection, caused by the lipophilic yeast Malassezia furfur (Malassezia globosa), classically produces hypopigmented or hyperpigmented macules on the trunk and proximal upper limbs that fail to tan because the organism disrupts melanocyte function and produces azelaic acid derivatives that inhibit melanin synthesis. It thrives in hot, humid tropical climates, explaining the Brazilian setting. The clinching diagnostic feature in the stem is the KOH skin scraping showing short hyphae with round yeast clusters, the pathognomonic "spaghetti and meatballs" appearance, which confirms Malassezia infection rather than a dermatophyte or non-infective cause. No further culture is needed as Malassezia is part of normal skin flora and culture adds no diagnostic value. Why the other options are wrong: D. Vitiligo: causes complete, well-demarcated depigmentation (loss of melanocytes) rather than partial hypopigmentation, and KOH microscopy would be entirely normal with no fungal elements. C. Leprosy: hypopigmented patches in leprosy are typically anaesthetic (sensory loss) due to nerve involvement, and skin smears would show acid-fast Mycobacterium leprae, not fungal hyphae and yeasts. B. Tinea corporis: dermatophyte infection produces annular, scaly, erythematous plaques with active advancing edges, and KOH shows only branching septate hyphae without the round yeast forms seen here. A. Post-inflammatory hypopigmentation: occurs after prior skin injury or dermatitis and has no associated fungal elements on microscopy; the stem gives no history of preceding inflammation. Key point: The combination of non-tanning hypopigmented truncal macules plus KOH showing "spaghetti and meatballs" hyphae and yeasts is diagnostic of pityriasis versicolor, not vitiligo or leprosy.

Reference: NICE Clinical Knowledge Summaries (CKS), Pityriasis versicolor, https://cks.nice.org.uk/topics/pityriasis-versicolor/