Probable invasive Alternaria rhinosinusitis in a previously healthy patient diagnosed with heterozygous CARD9 deficiency and combined immunodeficiency.

Alternaria is a dematiaceous mold emerging as a cause of invasive fungal infections in immunocompromised patients including invasive fungal rhinosinusitis. Prior case reports have described severe fungal infections in seemingly healthy patients later diagnosed with autosomal recessive CARD9 (caspase recruitment domain-containing protein 9) mutations. Here we report a case of invasive rhinosinusitis due to dematiaceous mold in a previously healthy patient with heterozygous CARD9 mutation and combined immunodeficiency cured with surgical resection and triazole therapy. The causative pathogen was most likely Alternaria species based on histopathologic findings and Next-Generation Sequencing results despite negative tissue cultures. We performed a retrospective review of all adult patients at our institution with Alternaria species identified by culture or polymerase chain reaction and found no other instances of invasive fungal rhinosinusitis. While highlighting the diagnostic dilemmas of our case, we present a comprehensive review of the available literature regarding management and clinical outcomes of dematiaceous mold infections, particularly invasive Alternaria rhinosinusitis, and the clinical implications of CARD9 deficiency.