An atypical mycobacterial infection while on Janus kinase inhibitor therapy

Janus kinase inhibitors are immunomodulatory drugs increasingly used to treat a broad range of inflammatory dermatologic conditions. Although effective, they carry a risk of serious adverse effects, including opportunistic infections. We present a patient who developed an atypical mycobacterial infection while on the Janus kinase 1 and Janus kinase 3 inhibitors, tofacitinib. A 76-year-old man was started on tofacitinib for a severe ulcerative colitis flare. Six weeks after starting therapy, he developed an erythematous papule on his right forearm that progressed into an ulcerating nodule. Initial biopsies suggested subcutaneous pyoderma gangrenosum. However, after failing multiple treatments, repeat biopsies and cultures were performed. An acid-fast bacilli stain was positive and specialized tissue cultures identified Mycobacterium chelonae. The lesions resolved after 6 weeks of clarithromycin therapy. This case highlights the immunosuppressive effects of Janus kinase inhibitors, which can lead to atypical infections including nontuberculous mycobacteria. Additionally, this case highlights the diagnostic challenges associated with these infections, which often require multiple biopsies and specialized microbiological techniques to diagnose. As the use of Janus kinase inhibitors expands, clinicians must maintain a high suspicion for atypical infections, particularly in patients with unusual dermatologic symptoms. Prompt diagnosis and intervention are essential to prevent complications.