A 51-year-old male, immunocompromised due to chronic lymphocytic leukemia and treatment with venetoclax and obinutuzumab, presented with a cavitary lung lesion and disseminated infection. Initial bronchoalveolar lavage microscopy revealed yeast, chlamydospores, and hyphae, leading to a presumptive diagnosis of a dimorphic fungus. However, subsequent culture and molecular testing identified the pathogen as Rhizopus arrhizus, causing disseminated mucormycosis. This case highlights the diagnostic challenge of distinguishing Mucorales from dimorphic fungi based solely on microscopy, emphasizing the critical role of definitive identification for appropriate antifungal therapy in immunocompromised patients.
Key note: Microscopic morphology alone can be misleading in fungal identification.