Black piedra is a superficial fungal infection of the hair shaft caused by Piedra hortae, an ascomycetous fungus forming hard black nodules on the shafts of the scalp, beard, moustache and pubic hair. It is common in Central and South America and South-East Asia.
Infections are usually localised to the scalp but may also be seen on hairs of the beard, moustache and pubic hair. Black piedra mostly affects young adults and epidemics in families have been reported following the sharing of combs and hairbrushes. Infected hairs generally have a number of hard black nodules on the shaft. Black piedra may be confused with trichorrhexis nodosa and trichonodosis but mycological examination will always confirm the diagnosis.
1. Clinical Material: Epilated hairs with hard black nodules present on the shaft.
2. Direct Microscopy: Hairs should be examined using 10% KOH and Parker ink or calcofluor white. Look for darkly pigmented nodules that may partially or completely surround the hair shaft. Nodules are made up of a mass of pigmented with a stroma-like centre containing asci.
3. Culture: Hair fragments should be implanted onto primary isolation media, like Sabouraud's dextrose agar. Colonies of Piedra hortae are dark, brown-black and take about 2-3 weeks to appear.
4. Serology: Not required for diagnosis.
5. Identification: Characteristic clinical, microscopic and culture features.
The usual treatment is to shave or cut the hairs short, but this is often not considered acceptable, particularly by women. In-vitro susceptibility tests have shown that Piedra hortae is sensitive to terbinafine and it has been successfully used, at a dose of 250 mg a day for 6 weeks, to treat a 23 year old Swedish Caucasian man following a 4 month visit to India (Gip, 1994).
Gip L, Black piedra: the first case treated with terbinafine. Br J Dermatol (1994) 130(Suppl.43):26-28.
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