Differential diagnosis of trichosporonosis using conventional histopathological stains and electron microscopy

Although Trichosporon is a causative pathogen of white piedra and summer-type hypersensitivity pneumonitis, fatal disseminated trichosporonosis cases have recently been increasing. However, Trichosporon is often confused with other fungi, especially Candida, in pathological specimens. The aim was to determine the utility of histopathological stains and electron microscopy for diagnosing trichosporonosis.

Autopsy cases of trichosporonosis, candidiasis, aspergillosis and cryptococcosis were investigated using histopathological stains and electron microscopy. Using Grocott's method, Trichosporon was weakly detected compared with other fungi. In contrast, diluted periodic acid methenamine silver (PAM) stain clearly enhanced the intensity of staining of Trichosporon compared with Candida. Furthermore, Alcian blue and colloidal iron stains predominantly detected Trichosporon. Electron microscopy after staining with diluted PAM demonstrated that Trichosporon has a variety of hyphal sizes and laminar deposition of rough silver granules, whereas Candida has uniform pseudohyphae and fine granules. The average diameter and population area of the granules were significantly higher in Trichosporon compared with Candida (P<0.01). Meanwhile, the laminar structure was preserved in the cell walls of Trichosporon without silver stains, whereas a low-density structure was observed in Candida.

Histopathological staining patterns and electron microscopic findings can facilitate the diagnosis of trichosporonosis.