What is piedra?
Piedra is a fungal infection of the hair, characterised by the deposition of small black or white nodules along the hair shaft. These look like small stones, hence the name piedra, meaning ‘stone’ in Spanish.
Piedra is also known as Trichomycosis nodosa or Trichomycosis nodularis.
There are two types: black piedra and white piedra, caused by different fungi and named because of the colour of fungal deposits they cause on the hair shaft.
Who gets piedra?
There is a lack of data on the incidence and prevalence of piedra.
- Appears to be no differences between the sexes.
- Can occur at any age, but is less common after middle age.
- Black piedra is more common in tropical regions, particularly South America and Southeast Asia.
- White piedra is more common in semitropical climates as well as temperate environments such as the Middle East, Africa, Europe, southern USA, and Japan.
Piedra is associated with:
- Poor personal hygiene
- Excessive use of topical hair oils
- Long hair
- Tight veil or scalp coverings use for extended periods of time.
What causes piedra?
The exact mechanism by which piedra is contracted is not well understood, however, it appears that anyone who is exposed to a causative fungus is at risk.
Piedra is caused by infection of the hair with certain fungi.
- Black piedra is caused by the fungus Piedraia hortae.
- White piedra is usually caused by Trichosporon spp., mainly T. cutaneum, T. ovoide, and T. inkin, and is also rarely caused by Acremonium and the bacteria of the Brevibacterium species.
What are the clinical features of piedra?
Patients with piedra have small, round, or ovoid nodules of fungus attached to or encircling the hair shafts. These can range in size from <1 millimetre (mm) to a few mm in diameter. Piedra typically occurs on scalp hair but can also be found in facial, armpit, and pubic hair.
- Brown to black coloured nodules
- Very firm and gritty to touch
- Well-attached to the hair shaft.
- White/off-white to light-brown coloured nodules
- Softer texture
- Easier to detach from the hair shaft.
Piedra is otherwise largely asymptomatic and patients do not typically report any pain or itch. A clinical clue for doctors to consider piedra is a negative ‘hair pull’ test. This suggests the problem is not at the root of the hair, but somewhere along the shaft.
How do clinical features vary in differing types of skin?
Although there are no documented racial, skin, or hair type predispositions for piedra, there may be an association with head coverings, such as the hijab.
What are the complications of piedra?
- P. hortae (the fungus causing black piedra) has strong keratolytic activity which allows it to break down the hair shaft. Over time, the fungus causes hair damage and breakage. Patients with untreated piedra may develop hair loss as a result.
- In those who are immunocompromised, piedra has been known to spread to the skin, causing purpuric or necrotic papules and nodules.
- In rare cases, Trichosporon asahii (one of the subtypes of fungus that causes white piedra) can also spread to the nails and even the lungs, causing onychomycosis and hypersensitivity pneumonitis.
How is piedra diagnosed?
- Trichoscopy — similar to dermoscopy, trichoscopy is the process of looking at hair under magnification. It is useful for excluding differential diagnoses such as head lice.
- Fungal culture — the gold standard for diagnosis. Strand(s) of hair are sent for culture and staining to visualise characteristic hyphae and/or spores.
What is the differential diagnosis for piedra?
- Pediculosis capitis (also known as head lice or nits)
- Tinea capitis
- Defects of the hair shaft (eg, trichorrhexis nodosa, or monilethrix)
- Trichomycosis axillaris (bacterial concretions adherent to the axillary hair)
What is the treatment for piedra?
- Good personal hygiene — regular hair washing and showering with dermatologist-recommended soaps and washes.
- Timely drying of hair — not leaving hair wet for extended periods of time.
- Avoid wrapping or covering hair while wet as this creates a moist environment in which the fungus thrives.
- Consider shaving hair in the affected region.
- Topical antifungal agents:
- Shampoos — application regimes may vary from once weekly for 3 weeks to twice daily for 12 weeks eg, 2% ketoconazole or 2% miconazole
- Lotions eg, ciclopirox (0.77%), selenium sulfide 1–2.5%, 6% precipitated sulphur in petroleum, Castellani paint, Amphotericin B, zinc pyrithione
- +/- addition of a keratolytic such as 1% salicylic acid.
- If these are ineffective, consider systemic antifungals eg, oral terbinafine or itraconazole.
How do you prevent piedra?
- Personal hygiene — regular washing of hairy body sites.
- Consider keeping scalp hair short, and regular shaving/waxing of body or facial hair.
- Avoid potential sources of the causative fungi. This includes hair brushes and pillows that were previously used during infection, to prevent reinfection.
- As person-to-person spread is rare, there are currently no recommendations for prophylactic treatment of close contacts of those with the condition.
What is the outcome for piedra?
Piedra is often chronic and can persist for years if left untreated. If treated, most patients will have a successful resolution.
Some types, particularly white piedra of the pubic region, have a higher rate of recurrence.