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Phaeohyphomycosis is an uncommon disease caused by dematiaceous fungi that is almost exclusively found in immunocompromised dogs. Here we describe the case of a dog treated with prednisone (1.1 mg/kg/day) and cyclosporine (11.2 mg/kg/day) for immune thrombocytopenia that developed cutaneous/subcutaneous lesions affecting both forelimbs 29 days after initiation of immunosuppression. The owner elected conservative outpatient treatment that consisted of wound care, antibiotics, mirtazapine, maropitant, and a dose reduction of prednisone (0.3 mg/kg/day) in lieu of biopsies or cultures. The dog was subsequently euthanized 13 days later because of an acute onset of increased respiratory rate and effort, obtunded mentation, and an inability to ambulate. Postmortem examination revealed widespread fungal dissemination in the heart, pericardium, intercostal muscles, lymph nodes, skin, subcutis, kidneys, lungs, pleura, and nasal cavity. Histopathology of the widespread plaques and nodules revealed fungal hyphae that were 4-8 µm in diameter, pigmented, variably septate, non-parallel, and toruloid with acute branching and occasional terminal bulbous dilations up to 20 µm in diameter, resembling chlamydoconidia. Yeast-like cells had a thick, variably pigmented wall and internal, foamy to granular, pale amphophilic contents. Fungal culture of swabs from the right elbow subcutaneous granulomas and from the left lateral pleural nodules yielded pure growth of Curvularia sp. Genomic DNA was extracted from harvested mycelia and molecular sequencing confirmed the presence of a novel Curvularia sp., C. arizonensis., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024. Published by Elsevier Inc.)