Abstract
A 76-year-old Japanese male with Castleman disease and autoimmune hemolytic anemia had been treated with rituximab (2,800 mg in total), tocilizumab (1,200 mg in total), and prednisolone (60.0 mg/day to 17.5 mg/day for nearly 4 years). He complained of edema of the left upper limb and skin ulcers on the left elbow and right shoulder. He was diagnosed with a cutaneous non-tuberculous mycobacterial infection. The causative agent was identified as Mycobacterium shigaense. This bacterium is a relatively new and rare non-tuberculous mycobacterium that was first reported in Shiga Prefecture in 2009. This case is the 10th reported case. Since it is phylogenetically close to M. simiae, it may have been misidentified until now. Of the 10 cases reported, includingour own case, the patient’s place of residence has been confirmed as beingShig a Prefecture in five cases, suggesting a very high regional characteristic. There have also been three reported cases in Osaka Prefecture. The bacterium was isolated from the water of Yodo River in Osaka, the only river that flows out of Lake Biwa in Shiga Prefecture. The pathogenicity is unclear ; however, in this case, immunosuppression and the use of biological agents were considered risk factors for its onset. Since this bacterium has a different antibiotic susceptibility profile to M. simiae, it is important to recognize it as an unclassifiable non-tuberculous mycobacterial infection. Skin Research, 24: 47-51, 2025
