Talaromycosis — DTM&H MCQ

Correct answer: B — Talaromyces marneffei infection

The correct answer is B, Talaromyces marneffei infection. This dimorphic fungus (formerly Penicillium marneffei) is endemic to Southeast Asia, southern China and northeast India, and in advanced HIV disease it causes disseminated infection with fever, weight loss and characteristic umbilicated skin papules that mimic molluscum contagiosum. The combination of geographic exposure (northern Thailand), advanced immunosuppression and a dimorphic fungus recovered on blood culture is the classic and most heavily tested vignette for talaromycosis, which behaves as a yeast at 37C and a mould at 25C on culture. Diagnosis relies on this thermal dimorphism plus recognition of the skin lesions, which are a key clinical clue distinguishing it from other papular dermatoses in HIV. Why the other options are wrong: A. Histoplasmosis: Also dimorphic and causes similar skin lesions in HIV, but Histoplasma capsulatum is endemic to the Americas and parts of Africa, not northern Thailand, making it geographically incorrect here. C. Molluscum contagiosum: Produces umbilicated papules but is caused by a poxvirus, not a dimorphic fungus, so it cannot grow on blood culture as described. D. Disseminated cryptococcosis: Cryptococcus neoformans is a yeast, not a dimorphic fungus, and typically presents with meningitis rather than umbilicated skin papules. E. Kaposi sarcoma: Caused by HHV-8, presents with violaceous vascular plaques or nodules rather than umbilicated papules, and is not a fungal organism, so it would never grow on culture. Key point: In a patient with advanced HIV, umbilicated skin papules plus a dimorphic fungus on culture from Southeast Asia (especially Thailand, Vietnam, southern China) points to Talaromyces marneffei, the classic AIDS-defining mycosis of that region.

Reference: Clinical review of cutaneous manifestations and diagnostic clues of Talaromyces marneffei in HIV patients, PubMed 2021, https://pubmed.ncbi.nlm.nih.gov/34651702/