Urano Shoko, Suzuki Yoko, Anzawa Kazushi, Ohishi Tsuyoshi, Kuroishi Shigeki, Itoh Naomi, Okada Takathika, Mochizuki Takashi
Department of Dermatology, Ensyu Hospital, Shizuoka, Japan.
Med Mycol J. 2014;55(4):J151-6. doi: 10.3314/mmj.55.J151.
In black fungal infections, Exophiala species are frequently encountered as causative agents of human mycosis, particularly in immunocompromised patients. Among them, Exophiala jenselmei was previously reported as the most common etiological agent. Advances in molecular taxonomy proved this taxon to be heterogeneous, and led to newly introduced or redefined species. Exophiala xenobiotica is one of the novel species differentiated from E. jenselmei on the basis of molecular phylogeny.Here, we report a case of pheomycotic cyst caused by E. xenobiotica, which was well controlled via drainage and local thermotherapy. A 70-year-old man developed a cystic nodular lesion on the dorsum of his right thumb over the previous 3 months. He had been treated with prednisolone and methotrexate for 4 years for rheumatoid arthritis. The patient also had lung cancer with vertebral bone metastasis. Direct microscopic examination of the greenish pus aspirated from the cyst revealed mycelial elements. Culture of the pus on blood and Sabouraud dextrose agar yielded numerous black colonies multiple times. Histopathological examination of a biopsy specimen showed subcutaneous abscess formation surrounded by granulomatous tissues. Faintly pigmented pseudohyphae were seen within the abscess. The presence of melanin in the fungal cells was determined by Fontana-Masson staining. Initial microscopic examination of the isolate revealed annellidic conidiogenous cells, suggestive of E. jenselmei. This strain was further identified as E. xenobiotica by sequence analysis of the internal transcribed spacer (ITS) region of ribosomal RNA, showing a 100% sequence homology with the strain type.Pheomycotic cysts should be considered on identifying a slowly developing chronic subcutaneous abscess in immunocompromised patients. Sequencing is recommended for accurate species identification of causative pathogens.
在黑色真菌感染中，外瓶霉属物种常作为人类真菌病的病原体被发现，尤其是在免疫功能低下的患者中。其中，詹氏外瓶霉曾被报道为最常见的病原体。分子分类学的进展证明该分类单元具有异质性，并导致了新引入或重新定义的物种。异物外瓶霉是基于分子系统发育与詹氏外瓶霉区分开来的新物种之一。在此，我们报告一例由异物外瓶霉引起的皮肤真菌囊肿病例，该病例通过引流和局部热疗得到了良好控制。一名70岁男性在过去3个月中右手拇指背侧出现了一个囊性结节性病变。他因类风湿关节炎接受泼尼松龙和甲氨蝶呤治疗4年。该患者还患有肺癌并伴有椎体骨转移。对从囊肿中抽出的绿色脓液进行直接显微镜检查，发现有菌丝成分。将脓液接种于血琼脂和沙氏葡萄糖琼脂上培养，多次长出大量黑色菌落。活检标本的组织病理学检查显示皮下脓肿形成，周围有肉芽肿组织。在脓肿内可见轻度色素沉着的假菌丝。通过Fontana-Masson染色确定真菌细胞中存在黑色素。对分离菌株的初步显微镜检查显示有瓶梗式产孢细胞，提示为詹氏外瓶霉。通过对核糖体RNA的内转录间隔区（ITS）区域进行序列分析，该菌株被进一步鉴定为异物外瓶霉，与模式菌株的序列同源性为100%。在免疫功能低下的患者中，当发现缓慢发展的慢性皮下脓肿时，应考虑皮肤真菌囊肿。建议进行测序以准确鉴定致病病原体的种类。
