Black Piedra (Piedraia)
Black piedra is a mycosis of the scalp hair endemic to tropical regions, such as South America and Indonesia. The causative agent of the disease is the fungus Piedraia hortae.
Clinical Features and Pathogenesis Fungi colonize the hair, actively invading the cuticle. Very hard, black nodules measuring about 1 mm in diameter form on the hair.
Pathogen Morphology An interesting feature of Piedraia hortae is the difference in its life cycles depending on its environment:
- In vivo (on the hair): The fungus undergoes sexual reproduction (teleomorph stage). Microscopy reveals dark brown, septate, branching hyphae 4–8 µm thick and asci—specific spore-containing sacs.
- In vitro (on Sabouraud agar): Only asexual reproduction (anamorph stage) occurs in culture. The fungus forms small, dark brown colonies with characteristic velvety margins. They consist of mycelium and chlamydoconidia.
Topical antifungal agents are successfully used to treat this mycosis.
White Piedra (Trichosporonosis)
White piedra is a hair shaft infection that, unlike black piedra, can affect not only the scalp hair but also the mustache and beard. Like black piedra, the disease is predominantly found in tropical countries.
Etiology and Clinical Presentation The causative agent is the fungus Trichosporon beigelii, which belongs to the Trichosporon cutaneum complex. When the infection develops, the hair cuticle is damaged, and hard nodules form around the hair shaft. By coalescing, they form a characteristic greenish-yellow sleeve wrapping around the hair.
Morphological and Cultural Characteristics
- Microscopic examination reveals septate hyphae about 4 µm thick.
- When cultured on Sabouraud agar, Trichosporon beigelii forms cream-colored or gray colonies with a wrinkled surface.
- The microstructure of these colonies is represented by septate mycelium, as well as arthroconidia and blastoconidia.
Treatment Approaches Treatment of white piedra is comprehensive:
- Pharmacotherapy: Azole antifungals and flucytosine are used.
- Mechanical and hygienic: Shaving the affected hair combined with strict personal hygiene is extremely effective and represents a crucial component of recovery.
Comparative Characteristics of Pathogens
For easy memorization, the main differences between the two types of piedra are summarized in the table below:
| Feature | Black Piedra | White Piedra |
|---|---|---|
| Pathogen | Piedraia hortae | Trichosporon beigelii |
| Nosology | Piedraia | Trichosporonosis |
| Localization | Scalp hair | Scalp, mustache, beard |
| Clinical Manifestation | Hard black nodules (~1 mm) | Greenish-yellow sleeve around the hair |
| Sabouraud Agar Colonies | Small, dark brown, velvety | Cream or gray, wrinkled |