The asteroid body of lobomycosis

Abstract

Obomycosis is a dermal mycosis produced by Loboa loboi. It gives rise to dermal granulomas in which giant cells phagocytose an overwhelming number of fungi. Intracytoplasmatic asteroid bodies (AB) have been observed in some giant cells. Their nature is unknown and they have been confused with the sporotrichotic AB. We studied 84 skin biopsies from 53 patients with lobomycosis, 7 by electron microscopy (EM). Immunohistochemistry with a polyclonal anti-Sporothrix schenckii antibody was performed in five biopsies. We found AB in the giant cells in 22 of the 84 biopsies on HE staining. They appeared as single eosinophilic intracytoplasmic structures surrounded by a clear empty space. This clear space did not appear when the biopsy was fixed with OsO₄, thus indicating that it is lipid in nature, and that the vacuole is an artefact produced by lipid extraction. Under the EM, the AB consist of bundles of dense, filamentous material, dense bodies and myelin structures resembling the image of AB in sarcoidosis. Some giant cells containing AB either phagocytosed only few fungi or did not contain any of them. The AB and the fungi did not react with the anti-sporotrichotic antibody, which stained the extracellular AB of sporotrichosis. These two asteroid structures are, therefore, different and unrelated phenomena.