Abstract: 【Abstract】 A 58-year-old female patient presented with red papules, plaques, and scabs on her right foot accompanied by pain and itching for 14 years. Dermatological examination revealed extensive red plaques on her right foot and ankle, with scattered red papules in between; some of the plaques were covered with a moderate amount of yellow-brown crusts, and a few yellow exudates were observed at the junction of the toes and the dorsum of the foot. Histopathological examination of the skin lesions showed hyperkeratosis, parakeratosis, pseudoepitheliomatous hyperplasia, neutrophil aggregation in the epidermis, and mixed inflammatory cell infiltration in the dermis. Three different types of colonies were cultured from the skin lesion tissues: light brown granular colonies, black granular colonies, and white-brown filamentous colonies. Under the microscope, the filamentous colonies appeared as long chains of brown conidia with short cylindrical beaks, while the black and light brown granular colonies appeared as clusters of spores, with single or multiple septa inside, and some budding spores were observed. Electron microscopy further confirmed the above structures. Molecular biological analysis revealed that the three types of colonies were all identified as Alternaria alternata. The patient was diagnosed with cutaneous alternariosis caused by a special form of Alternaria alternata. After 7 months of treatment with oral itraconazole, the skin lesions healed, and no recurrence was observed during a 3-year follow-up.

Key words: Alternariosis, Alternaria alternata, Meristematic growth, Ultrastructure, Animal experimentation