Piedra refers to colonization of the hair shaft that results in firm, irregular nodules. If the nodule is dark, the infection is Black Piedra and is due to N/A(L):Piedra iahortae. The nodule is the ascomycete fruiting body of the fungus, know as an ascostroma. If the nodule is white, the infection is White Piedra and is due to Trichosporon beigelii.
These nodules are a loose aggregate of hyphae and arthroconidia. Multiple colonization of the same strand are common. The infection may affect hairs of the scalp, body and genital areas [741, 1145, 2155]. The source of infection is unknown and even though person to person transmission has been suggested, it rarely occurs [884, 1145, 1447].
Both clinical varieties are mostly asymptomatic. However, according to the severity of the infection, progressive weakness of the hair shaft will occur causing breaks.
In black piedra, brown to black nodules will be firmly adherent to the shaft and cannot be readily detached. The area most frequently involved is the scalp. Indeed, a metallic sound may be heard when the hair is combed.
In white piedra, the nodules are easily detached from the hair shaft by rubbing along its length. Their color varies from white to light brown. Pubic hair, beard and mustache are the most commonly infected areas .
Differential diagnosis for both conditions includes pediculosis capitis, pubis louse infestations, trichorrhexis nodosa, trichomycosis axillaris and monilothrix .
Prognosis and therapy
Therapy includes shaving of affected areas or topical application of salycylic acid, 2% formaldehyde or azole creams. Oral therapy with either ketoconazole or terbinafine has also been used. However, relapse rates are high even after adequate therapy [842, 1145].