Tinea Nigra Workup

Updated: May 12, 2020
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: William D James, MD  more...
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Workup

Procedures

Microscopic examination of skin scrapings treated with 20% KOH reveals thick, septate, branching hyphae that contain a dark pigment in their walls. Blastospores or chlamydoconidia may also be present.

Culture of skin scrapings on Sabouraud agar at 25°C yields growth in approximately 1 week. Initially, yeastlike colonies that are shiny, black, and mucoid are present. Subsequently, the colonies become olivaceous brown and develop aerial mycelia in 2-3 weeks. Microscopic examination of the colonies reveals dematiaceous 2-celled yeast that produce annelloconidia in addition to dematiaceous, septate hyphae with conidia on intercalary annelides.

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Histologic Findings

Examination of biopsy specimens reveals hyperkeratosis and mild acanthosis. Periodic acid-Schiff (PAS)–positive septate hyphae are present in the stratum corneum. A scant amount of perivascular lymphocytic infiltrate may be found in the papillary and subpapillary layers of the dermis. Note the images below.

Tinea nigra, showing hyperkeratosis and mild acant Tinea nigra, showing hyperkeratosis and mild acanthosis. A scant amount of perivascular lymphocytic infiltrate may be found in the papillary and subpapillary layers of the dermis (hematoxylin and eosin stain). Courtesy of Thomas N. Helm, MD.
Tinea nigra, with histologic section demonstrating Tinea nigra, with histologic section demonstrating periodic acid-Schiff–positive septate hyphae within the stratum corneum. Courtesy of Thomas N. Helm, MD.
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