Nontuberculous Mycobacterial Infection Mimicking Inflammatory Tenosynovitis: A Real Head Scratcher.

Nontuberculous mycobacterial tenosynovitis is a rare entity that is often misdiagnosed as bacterial or inflammatory tenosynovitis. We present a case of a 64-year-old man who presented with pain and swelling of his right wrist for several weeks. Magnetic resonance imaging (MRI) of his right upper extremity showed findings consistent with prominent tenosynovitis in the right extensor digitorum tendon sheath. Surgical debridement showed reactive histopathology with negative Gram stain, culture, and acid-fast bacilli stain; after which, steroids were started along with methotrexate and hydroxychloroquine, which was later changed to anti-tumor necrosis factor (anti-TNF) therapy. Due to minimal improvement, repeat operative debridement was done showing macroscopic rice bodies with pathology revealing chronic granulomatous inflammation with necrosis. However, repeated infectious work-up remained negative. After his symptoms progressed to involve his right index finger, his tenosynovium was sampled again, which was positive for acid-fast bacilli (AFB) staining for rare mycobacterial organisms, with cultures growing faint transparent colonies that were sent to the state laboratory for speciation. He was started on empiric therapy with clarithromycin, ethambutol, and rifampin following which his wound fully healed. This case illustrates the insidious course of nontuberculous mycobacteria (NTM) tenosynovitis leading to delayed diagnosis along with unwarranted treatments that could be harmful. Open tissue biopsy is important in the context of a lack of clinical response to common treatment modalities, in the absence of an alternative diagnosis with a similar clinical picture.