In situ hybridization for Aspergillus and Penicillium in allergic fungal sinusitis: A rapid means of speciating fungal pathogens in tissues

Allergic fungal sinusitis (AFS) is a serious form of sinonasal fungal disease that is commonly associated with Aspergillus or Dematiaceous fungi, This study was performed to determine the incidence of Aspergillus or Penicillium in AFS by using in situ hybridization (ISH) for Aspergillus and Penicillium ribosomal RNA (rRNA). The Fontana-Masson melanin stain (FMMS) was also used to detect pigmented fungi (A. niger and Dematiaceous fungi), ISH was performed on 26 patients: 17 AFS cases with histologic evidence of fungi, 5 AFS cases without histologic evidence of fungi, 3 cases of invasive fungal sinusitis (IFS), and I case of fungus ball. Nine AFS specimens with histologic evidence of fungi were ISH positive, Positivity was also noted in two of three IFS cases, while no staining was seen in the fungus ball and in six AFS specimens without fungi demonstrable by silver stains, Six ISH-positive cases were FMMS positive, suggesting A. niger. Five ISH-negative AFS specimens were FMMS positive, suggesting Dematiaceous fungi, In summary, many AFS patients in our institution demonstrate Aspergillus/Penicillium organisms. Ancillary techniques may help identify fungi responsible for AFS if cultures are negative or not performed, ISH for rRNA is a useful means for rapidly speciating fungi in human tissues.