Molecular identification of <i>Fonsecaea pedrosoi</i> in chromoblastomycosis: Insights from paraffin-embedded human skin biopsies and clinicopathology

Chromoblastomycosis (CBM) is a chronic fungal infection caused by dematiaceous fungi. In some cases, culture methods fail to identify the fungal species, and fresh tissue for molecular identification is unavailable. The use of molecular techniques on formalin-fixed, paraffin-embedded (FFPE) samples can aid in identifying the causative agent. This study aimed to identify fungal species in histopathologically confirmed cases of CBM using PCR and sequencing of 18S-ITS1-5.8S-ITS2-28S rDNA region of FFPE skin biopsies and to describe their clinicopathological features. This retrospective study used FFPE samples from nine CBM patients from remote regions of Mexico. The samples were submitted to the Mycology Section at the Hospital General "Dr. Manuel Gea González" (2000-2016) for molecular identification of the causative agent and characterization of clinicopathological features. Lesions were most commonly located on the forearm (four cases), with one case each on the buttock, back, foot, and leg. One patient presented with cutaneous dissemination. Verrucous plaques were observed in 88.9% of cases. Histology and direct examination confirmed CBM, showing muriform cells and varying degrees of dermal fibrosis in all cases. DNA extracted from FFPE samples was amplified and sequenced in the 18S-ITS1-5.8S-ITS2-28S rDNA region, identifying Fonsecaea pedrosoi with 100% homology in all cases. This study identifies F. pedrosoi as the predominant pathogen of CBM in the evaluated samples of Mexican origin and demonstrates the reliability of molecular identification using FFPE samples.