White Piedra

White piedra is a superficial fungal infection of the hair shaft caused by Trichosporon species. The fungus forms soft, pale, loosely adherent nodules or sleeves on the outer surface of the hair. The skin is not infected. It is asymptomatic and cosmetic, and the principal clinical task is to distinguish it from lice nits, hair casts and bacterial concretions.

It is a different disease from invasive trichosporonosis, which occurs in neutropenic and critically ill patients and from the superficial colonisation of the skin that precedes it. White piedra does not itself indicate immunodeficiency.

Epidemiology:

• Worldwide, with greater frequency in tropical, subtropical and temperate humid regions, including South America, Africa, Asia, southern Europe and the southern United States.
• Genital white piedra (pubic hair) is the commonest form reported in many series. Scalp, beard, moustache, axillary and eyebrow hair may also be affected.
• Occurs in young adults, and the genital form may be sexually transmitted or acquired through shared towels, with the organism also a skin and genital commensal.
• Poor hair hygiene, humidity and sweating predispose.

Trichosporon belongs to the Basidiomycota (class Tremellomycetes). Taxonomy was revised on sequence data, and the older name Trichosporon beigelii is no longer used.

Microbiological features:

• Yeast like basidiomycete producing true hyphae, pseudohyphae, blastoconidia and arthroconidia together, which is characteristic of the genus.
• Arthroconidia are rectangular or barrel shaped, formed by fragmentation of hyphae.
• Urease positive and diazonium blue B positive, in common with other basidiomycetous yeasts.
• Growth on Sabouraud dextrose agar at 25 to 30 degrees Celsius within 2 to 5 days. Colonies are cream to white, dry, wrinkled and later folded or cerebriform, with a powdery surface. Cycloheximide inhibits Trichosporon, so media with cycloheximide are avoided. Most clinically important species also grow at 37 degrees Celsius.
• Species level identification requires sequencing of the intergenic spacer 1 region or MALDI TOF mass spectrometry, because internal transcribed spacer sequencing does not separate closely related species well.
• Intrinsically resistant to echinocandins.

Trichosporon species colonise skin and the perineum in some healthy people. In warm humid conditions, the fungus settles on the hair cuticle and grows around the shaft, forming a nodule cemented by fungal and host material. Growth is on the outer surface, with hyphae occasionally penetrating the cuticle but not the cortex. Little or no inflammation accompanies the disease.

Hair shafts are not weakened as in black piedra, and breakage is uncommon.

• Soft, loosely attached nodules or sleeves along the hair shaft, white, cream, light brown or greenish, ranging from under 1 mm to a few millimetres.
• Nodules are easily detached by scraping or combing, which separates them from nits and black piedra.
• Scalp hair, beard, moustache, axillary and pubic hair may be affected, often with several sites involved.
• No symptoms. Mild pruritus occurs in some, usually from associated conditions.
• Associated trichomycosis, bacterial infection of the same hair, is common in axillary and pubic hair.

• Specimen: hair clippings bearing nodules.
• Potassium hydroxide preparation (10 to 20 percent), or calcofluor white: nodules show a sheath of fungal elements around the shaft: hyaline septate hyphae fragmenting into rectangular arthroconidia, with blastoconidia, arranged perpendicular to the shaft. Nodules are softer than those of black piedra and have no asci.
• Culture: Sabouraud dextrose agar without cycloheximide at 25 to 30 degrees Celsius, with growth in 2 to 5 days. Culture allows species identification, which has some value because Trichosporon inkin and Trichosporon ovoides are the usual piedra species and Trichosporon asahii is the usual invasive species.
• Histopathology: not required.
• Differentiation from trichomycosis: Gram stain or direct microscopy shows bacteria in trichomycosis and fungal elements in white piedra, and the two may coexist.

Cutting or shaving the affected hair removes the infection and is the most reliable cure. In genital disease, the whole pubic area is shaved or clipped and all involved hair treated, because incomplete treatment is a common cause of relapse.

Topical therapy for hair that is retained:

Oral azoles (itraconazole or fluconazole) have been used in refractory cases in case reports. Evidence is limited, and oral therapy is seldom needed. Terbinafine and the echinocandins are inactive against Trichosporon. Amphotericin B has reduced activity against the genus, which is relevant in invasive disease but not in piedra.

Relapse follows persisting humidity and poor hygiene. Combs, brushes, towels and razors should not be shared. Where the genital form is present, sexual partners can be examined, and coexisting trichomycosis is treated with its own measures (shaving and an antibacterial wash).