Sensitivity and specificity of immunohistochemistry for the diagnosis of filamentous fungal infections.

Abstract

Many fungal species share overlapping morphologic features in tissue sections, preventing reliable identification and optimal treatment. We sought to determine whether immunohistochemistry (IHC) using a panel of commercially available antibodies could effectively distinguish between fungi commonly encountered in anatomic pathology specimens. Anti-Aspergillus, anti-Rhizopus, and anti-Candida IHC was performed on formalin-fixed, paraffin-embedded tissue sections from 24 cases with fungal infections identified by culture or sequencing (including 4 polyfungal infections). Anti-Aspergillus IHC was positive in 6 of 6 Aspergillus and focally in 1 of 4 Candida species infections and negative in all cases of Fusarium, Scedosporium, Rhizopus, and Mucor species, yielding overall sensitivity of 100% and specificity of 95%. Anti-Rhizopus IHC was positive in 4 of 4 Rhizopus and 1 of 3 Mucor species infections and negative in all other cases, with a sensitivity of 71% and a specificity of 100%. Anti-Candida IHC was positive in 4 of 4 Candida species infections and showed some cross-reactivity in all other cases, resulting in 100% sensitivity and 0% specificity. Anti-Aspergillus IHC was highly sensitive and specific in its ability to distinguish Aspergillus from other similar-appearing hyaline molds, including Fusarium and Scedosporium species. Anti-Rhizopus IHC was moderately sensitive and highly specific, while anti-Candida IHC was highly sensitive but had minimal specificity.