Diagnostic value of fluorescein-labeled chitinase staining in formalin-fixed and paraffin-embedded tissues of fungal disease.

Common histopathologic techniques are used to diagnose fungal infections, but the diagnostic identification of mycoses in tissue specimens is often difficult, particularly when fungi rarely occur in a specimen. The aim of this study was to evaluate the application of fluorescein-labeled chitinase staining to formalin-fixed and paraffin-embedded (FFPE) tissues. We studied 79 archival FFPE tissues from patients diagnosed with fungal disease, including 38 cases of sporotrichosis and 41 cases of other fungal infections. The tissue sections were subjected to periodic acid-Schiff (PAS) staining, Gomori's methenamine silver (GMS) staining, and fluorescein-labeled chitinase staining to detect fungal elements. Culture- and/or hematoxylin-eosin-positive samples were used to estimate the diagnostic sensitivity of each staining method, with the results showing that PAS, GMS, and fluorescein-labeled chitinase staining had sensitivities of 50.6, 70.9, and 68.4%, respectively. The three staining results were the same for all fungal infections except for sporotrichosis and chromoblastomycosis. Fluorescein-labeled chitinase staining exhibited high sensitivity in cases of sporotrichosis and poor performance in detecting muriform cells of chromoblastomycosis. On the whole, the sensitivity of fluorescein-labeled chitinase staining was greater than that of PAS and similar to that of GMS staining. Therefore, the results of our study suggest that fluorescein-labeled chitinase staining is a potentially useful diagnostic tool in the diagnosis of fungal infections.