Phaeohyphomycosis due to Alternaria spp. and Phaeosclera dematioides: a histopathological study.

A case of phaeohyphomycosis caused by strains of both Alternaria spp. and Phaeosclera dematioides is presented. The biopsy material was studied using histological, immunohistochemical and transmission electron microscopy techniques. The agent's dematiaceous mycelia are composed of thick-walled hyphae, branched and unbranched, with terminal vesicular formations. All the described structures occur alone or in chains within multinuclear giant foreign body-type cells or invading an abscess. Also present are budding forms. Immunostaining of histiocytic inflammatory cells in either. diffuse or granulomatous infiltrates revealed cytoplasmic positivity for lysozyme and Ki-MIP antibody. The lymphocytic infiltrates of the upper corium show predominantly small T lymphocytes (CD3 and CD45RO positive) and absence of CD20-positive B cells. Plasma cells occurring within the infiltrates of the deeper parts show polyclonal expression of both Ig light chains.