低温培養を追加し診断に至った播種性皮膚Mycobacterium chelonae感染症の1例

Mycobacterium chelonae is a rapidly growing nontuberculous mycobacterium and a rare cause of cutaneous infection in both immunocompromised and immunocompetent patients. The skin lesions are non-specific in nature, so that the infection remains underdiagnosed and diagnosis is often delayed. Herein, we report the case of an 83-year-old immunocompromised woman with a 6-month history of persistent skin lesions. The lesions were previously misdiagnosed and treated as herpes zoster, and even as bullous pemphigoid, for which she received prednisone. Ziehl-Neelsen staining of biopsy specimens from the subcutaneous nodules on the right forearm and dorsum of the left foot revealed acid-fast bacilli. Culture on blood agar medium under low-temperature conditions yielded colonies after 6 days. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry allowed identification of M. chelonae; the results were consistent with that of 16S rRNA gene sequencing analysis. Therefore, we made the diagnosis of disseminated cutaneous M. chelonae infection and initiated the patient on combined clarithromycin, moxifloxacin, and amikacin therapy. The findings in this case indicate that clinicians should consider mycobacterium-related infections in patients with intractable skin lesions. To obtain a proper microbiological diagnosis, good collaboration between clinicians and clinical laboratory technicians is necessary, with collection of appropriate specimens and use of appropriate stains and culture conditions, bearing in mind the suspected microorganisms.