Narrow-spectrum staining pattern of Pityrosporum

Background: Broad-spectrum fungal stains are used to detect fungal organisms, but narrow-spectrum stains can assist in fungal differential diagnosis. These stains include mucicarmine and Fontana-Masson ( FM) for Cryptococcus, Alcian Blue for Cryptococcus and Blastomyces, Congo Red for Blastomyces and Coccidioides, and Ziehl-Neelsen for some examples of Blastomyces and Histoplasma. Pityrosporum is increasingly being recognized as a pathogen capable of significant cutaneous and systemic infections, but the narrow-spectrum staining pattern of Pityrosporum has not yet been systematically studied and reported. Methods: Paraffin-embedded archival tissue from 10 skin biopsies containing Pityrosporum was stained with Alcian Blue, Congo Red, Ziehl-Neelsen acid-fast stain, and FM stain. In addition to the 60-min staining time, a modified FM stain with 15-, 30-, and 45- min staining times was also performed. Results: All cases stained positive with Alcian Blue, Congo Red, and FM stains and negative with the Ziehl-Neelsen stain. The modified FM stain with the 15- min staining time showed significant staining in more than 50% of the cases. Discussion: The narrow-spectrum staining pattern of Pityrosporum distinguishes it from Cryptococcus, Blastomyces, Candida, Histoplasma, and Coccidioides.