Histopathology of cutaneous sporotrichosis in Rio de Janeiro: a series of 119 consecutive cases

Background: Sporotrichosis is the most common subcutaneous mycosis in Rio de Janeiro. Histopathological examination reveals diffuse granulomatous and suppurative dermatitis, and the fungus is rarely identifiable in tissue. We describe the histopathological features of cutaneous sporotrichosis, and investigate the association between them and the lack of visualization of the fungus. Methods: A total of 119 samples of confirmed sporotrichosis cases were studied. The characteristics of the inflammatory infiltrate, the presence of epidermal changes, necrosis and fibrosis, and the parasite burden were analyzed. The association between histopathological changes and the lack of visualization of the fungus was evaluated using prevalence ratios. Results: Granulomas were observed in all samples, suppurative granulomas in 100 (84%) and diffuse dermatitis in 114 (95.8%). Liquefaction and caseous necrosis were present in 78 (65.5%) and 52 (43.7%) samples, respectively. The fungus was not seen in 77 (64.7%) samples. Epithelioid, tuberculoid or foreign-body-type granulomas, caseous, fibrinoid or absent necrosis, predominance of lymphocytes among nonphagocytic cells and fibrosis were associated with the lack of visualization of the fungus. Conclusion: The histopathological characteristics of sporotrichosis were variable when the causative fungus was not seen. In a proper context, the diagnosis of sporotrichosis remains a potential consideration even in the absence of demonstrable yeast.