A man in his 70s presented with a 6-month history of a rash on the left forearm, which gradually increased in severity. The patient developed a rash on the dorsal aspect of his hand half a year ago without any pain or itching discomfort and denied any history of injury or exposure to suspected pathogens prior to onset. After self-medication with topical herbal medicine, the lesions gradually spread to the forearm and fused into plaques, and ulcers often recurred on the surface. He denied any systemic symptoms and concerns. Physical examination revealed large, firm, mildly swollen erythematous plaques on the back of the left forearm with purulent discharge and crusting (Figure, A). Results of routine laboratory investigations, including complete blood cell count, biochemical profile, and chest radiography, were normal. A biopsy specimen was taken for pathological examination (Figure, B-D).
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C. Cutaneous protothecosis
Hyperkeratosis, pseudoepitheliomatous hyperplasia, and a lymphohistiocytic infiltrate with granuloma formation, neutrophils, plasma cells, and multinucleated giant cells in the dermis were observed in the pathological examination (Figure, B). Periodic acid–Schiff staining showed mulberrylike thick-walled spherical or ovoid spores of various sizes and high-density cell walls (Figure, C). Multiple endospores were highlighted by transmission electron microscopy and were irregular asexually separated schizonts (Figure, D). After identification of Protothecosis wickerhamii by molecular sequencing technology, the diagnosis of protothecosis was confirmed. One month after oral administration of itraconazole, 0.2 g, every day, the patient’s rash subsided considerably.
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Corresponding Author: Borui Chen, MD, PhD, Dermatology Institute of Fuzhou, Dermatology Hospital of Fuzhou, Xihong Rd 243, Fuzhou 350025, China (email@example.com).
Published Online: November 9, 2022. doi:10.1001/jamadermatol.2022.4889
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank the patient for granting permission to publish this information. We also thank Jun Chen, MD, Liqiang Weng, MD, and Qinqin Long, MD, all from the Dermatology Hospital of Fuzhou, for their assistance in pathology; Wanding Lu, MD, from the Dermatology Hospital of Fuzhou, for assisting in professional guidance and comments on this case; and Xi Lin, MS, from the Public Technology Service Center of Fujian Medical University, for support in transmission electron microscopy. They were not compensated for their contributions.
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