Black Piedra

Black piedra is a superficial fungal infection of the hair shaft caused by Piedraia hortae. The fungus forms hard, black, firmly adherent nodules on the outer surface and cuticle of scalp hair. The scalp skin is not infected. Piedra is the Spanish word for stone, which describes the gritty, hard feel of the nodules.

The infection is cosmetic and asymptomatic. The clinical problem is recognition and distinction from other hair concretions, and the treatment is mainly removal of the infected hair.

Epidemiology:

• Humid tropical and subtropical regions: the Amazon basin and other parts of Central and South America, central and West Africa, South and Southeast Asia and the Pacific islands.
• Predominantly rural populations, children and young adults.
• Scalp hair is the usual site. Beard, moustache and pubic hair are rarely affected.
• Occurs in settings where hair is oiled and infrequently washed, humidity is high, and combs and hair ornaments are shared.

Piedraia hortae belongs to the Ascomycota (order Capnodiales, family Piedraiaceae). It is a dematiaceous fungus that forms a true sexual stage on the hair in the form of asci, a feature that distinguishes it from the white piedra organisms.

Microbiological features:

• Environmental fungus of soil and vegetation in tropical climates. The precise reservoir and mode of acquisition are not established. Contact with soil, plants, contaminated combs and shared grooming items is the proposed route.
• Nodules consist of a dense stroma of brown, thick walled, septate hyphae cemented together, with asci arranged in locules inside the stroma.
• Each ascus contains up to 8 ascospores, and they are spindle shaped, curved, with a filamentous tail at one or both ends.
• Culture on Sabouraud dextrose agar at 25 to 30 degrees Celsius gives slow growing, compact, dark olive to black, folded, glabrous or velvety colonies with a brown to black reverse, over 2 to 3 weeks. Microscopy shows brown, septate, toruloid hyphae with arthroconidia and chlamydoconidia. Ascospores form rarely in culture.
• Fontana Masson positive because of the melanin in the wall.

Piedraia quintanilhae is a related species that infects non human primates and is not a human pathogen.

Fungal cells settle on the cuticle of hair shafts, where humidity and hair oils sustain growth. Hyphae grow between and beneath cuticle scales and aggregate into a nodule. The nodule then cements itself to the shaft. Hyphae may weaken the cortex at the site of the nodule, so the hair occasionally fractures there, but the fungus does not invade the follicle or living tissue, and there is no inflammatory response.

• Multiple hard, dark brown to black nodules, up to about 1 to 2 mm in size, firmly attached to the hair shaft.
• Nodules are gritty, can be felt when the hair is rolled between the fingers, and may produce a metallic clicking sound when the hair is combed.
• Nodules can fuse into a sheath around the shaft.
• Hair shaft may be weakened, and may break at the nodule.
• Scalp skin appears normal, and there is no itching.
• Many family members may be affected where grooming items are shared.

• Specimen: hair clippings carrying nodules, taken with scissors from the scalp.
• Potassium hydroxide preparation (10 to 20 percent): the nodule is crushed under the coverslip after gentle heating. It shows a mass of dark, thick walled, septate hyphae in a stroma, with asci containing curved ascospores. The ascus containing ascospores is diagnostic and distinguishes black from white piedra. Intact nodule shows pigmented hyphal masses running perpendicular to the shaft.
• Culture: Sabouraud dextrose agar with chloramphenicol, 25 to 30 degrees Celsius. Growth is slow, and cultures should be held for at least 3 weeks.
• Molecular identification: internal transcribed spacer sequencing identifies the species where microscopy is not conclusive.

Cutting or shaving the hair is the most effective measure and results in prompt cure. This is acceptable for children and in settings where short hair is customary, and it is the usual first step for localised disease. When hair is kept long, topical therapy is added:

Oral terbinafine 250 mg daily for 6 weeks has been used successfully in case reports for extensive or recurrent disease. Evidence is limited to case reports, so oral therapy is reserved for failure of hair cutting and topical therapy.

Recurrence is frequent if humidity and hair oiling continue and combs are shared. Combs and brushes should be cleaned and not shared. Family members should be examined, because affected people commonly share grooming habits.