A young man presents with hard, black nodules adherent to the shafts of his scalp hairs. Hair washing does not remove them. KOH examination of the nodules shows a mass of darkly pigmented, cemented ascostromata containing asci. Which organism is responsible?
- A Malassezia furfur
- B Trichosporon asahii
- C Piedraia hortae ✓
- D Hortaea werneckii
Correct answer: C. Piedraia hortae
Explanation
Black piedra is caused by Piedraia hortae, an ascomycete that forms firm, dark, stony nodules on scalp hair composed of cemented ascostromata containing asci and ascospores. White piedra, caused by Trichosporon asahii, produces soft, pale, easily detachable nodules on beard, moustache, and pubic hair without ascostromata. Malassezia causes pityriasis versicolor, and Hortaea werneckii causes tinea nigra, a dark macular infection of the palm, not hair nodules.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.