PCR sequencing and re-evaluation of pathologic findings revealed invasive fungal sinusitis caused by Malassezia restricta.

Objective: To describe a rare case of invasive fungal sinusitis caused by Malassezia restricta in a patient with diabetes and emphasize the diagnostic difficulties and significance of molecular techniques.

Study Design: An 85-year-old man with diabetes presented with unresolved left sphenoiditis despite a sphenoidotomy and antibiotics. Imaging findings indicated invasive fungal sinusitis. Pan-fungal polymerase chain reaction and sequencing along with special stains (Gomori methenamine silver and Periodic acid-Schiff) were used for the diagnosis.

Results: An initial pathological examination revealed necrotic tissue without visible fungal elements; fungal cultures were negative. Pan-fungal polymerase chain reaction identified M. restricta, and subsequent staining confirmed fungal invasion. The patient was treated with voriconazole, which led to a complete recovery and vision restoration.

Conclusion: This case highlights the value of molecular diagnostics and detailed pathological analysis in diagnosing rare fungal infections. The early and accurate identification of Malassezia infections allows effective treatment, ultimately improving patient outcomes.