Black Adherence Nodules on the Scalp Hair Shaft

The Diagnosis: Piedra

Microscopic examination of the hair shafts revealed brown to black, firmly adherent concretions (Figure 1). Scanning electron microscopy of the nodules was performed, which allowed for greater definition of the constituent hyphae and arthrospores (Figure 2).

^{Photograph courtesy of Eric Hossler, MD (Danville, Pennsylvania).}

Figure 1. Piedra findings on microscopic examination of the hair shafts under light microscopy including brown to black firmly adherent concretions (A and B)(original magnifications ×100 and ×400).

^{Photograph courtesy of Fred E. Hossler, PhD (Johnson City, Tennesse).}

Figure 2. Piedra findings on scanning electron microscopy of the nodules allowed for greater definition of the constituent hyphae and arthrospores.

Fungal cultures grew Trichosporon inkin along with other dematiaceous molds. The patient initially was treated with a combination of ketoconazole shampoo and weekly application of topical terbinafine. She trimmed 15.2 cm of the hair of her own volition. At 2-month follow-up the nodules were still present, though smaller and less numerous. Repeat cultures were obtained, which again grew T inkin. She then began taking oral terbinafine 250 mg daily for 6 weeks.

This case of piedra is unique in that our patient presented with black nodules clinically, but cultures grew only the causative agent of white piedra, T inkin. A search of PubMed articles indexed for MEDLINE using the terms black piedra, white piedra, or piedra, and mixed infection or coinfection yielded one other similar case.¹ Kanitakis et al¹ speculated that perhaps there was coinfection of black and white piedra and that Piedraia hortae, the causative agent of black piedra, was unable to flourish in culture facing competition from other fungi. This scenario also could apply to our patient. However, the original culture taken from our patient also grew other dematiaceous molds including Cladosporium and Exophiala species. It also is possible that these other fungi could have contributed pigment to the nodules, giving it the appearance of black piedra when only T inkin was present as the true pathogen.

White piedra is a rare fungal infection of the hair shaft caused by organisms of the genus Trichosporon, with Trichosporon ovoides most likely to infect the scalp.² Black piedra is a similar fungal infection caused by P hortae. Piedra means stone in Spanish, reflecting the appearance of these organisms on the hair shaft. It is common in tropical regions of the world such as Southeast Asia and South America, flourishing in the high temperatures and humidity.² Both infectious agents are found in the soil or in standing water.³ White piedra most commonly is found in facial, axilla, or pubic hair, while black piedra most often is found in the hair of the scalp.^2,4 Local cultural practices may contribute to transfer of Trichosporon or P hortae to the scalp, including the use of Brazilian plant oils in the hair or tying a veil or hijab to wet hair. Interestingly, some groups intentionally introduce the fungus to their hair for cosmetic reasons in endemic areas.^2,3,5

Patients with white or black piedra generally are asymptomatic.⁴ Some may notice a rough texture to the hair or hear a characteristic metallic rattling sound as the nodules make contact with brush bristles.^2,3 On inspection of the scalp, white piedra will appear to be white to light brown nodules, while black piedra presents as brown to black in color. The nodules are often firm on palpation.^2,3 The nodules of white piedra generally are easy to remove in contrast to black piedra, which involves nodules that securely attach to the hair shaft but can be removed with pressure.^3,5 Piedra has natural keratolytic activities and with prolonged infection can penetrate the hair cuticle, causing weakness and eventual breakage of the hair. This invasion into the hair cortex also can complicate treatment regimens, contributing to the chronic course of these infections.⁶

Diagnosis is based on clinical and microscopic findings. Nodules on hair shafts can be prepared with potassium hydroxide and placed on glass slides for examination.⁴ Dyes such as toluidine blue or chlorazol black E stain can be used to assist in identifying fungal structures.² Sabouraud agar with cycloheximide may be the best choice for culture medium.² Black piedra slowly grows into small dome-shaped colonies. White piedra will grow more quickly into cream-colored colonies with wrinkles and sometimes mucinous characteristics.³

The best treatment of black or white piedra is to cut the hair, thereby eliminating the fungi,⁷ which is not an easy option for many patients, such as ours, because of the aesthetic implications. Alternative treatments include azole shampoos such as ketoconazole.^2,4 Treatment with oral terbinafine 250 mg daily for 6 weeks has been successfully used for black piedra.⁷ Patients must be careful to thoroughly clean or discard hairbrushes, as they can serve as reservoirs of fungi to reinfect patients or spread to others.^5,7