Tenosynovitis Caused by a Novel Nontuberculous Mycobacterium Species Initially Misidentified as a Member of the Mycobacterium tuberculosis Complex

We present a case of tenosynovitis caused by a novel, slowly growing, nonchromogenic, nontuberculous mycobacterium (NTM). Originally misidentified asMycobacterium tuberculosis complex, the NTM cross-reacts with theM. tuberculosis complex nucleic acid hybridization probe, aM. tuberculosis gamma interferon release assay, and is closely related toM. tuberculosis by 16S rRNA gene sequencing. CASE REPORT A58-year-old previously healthy female presented to her pri-mary care physician with right thumb pain, swelling, warmth and erythema, and a blister at the base of the thumb. The lesion did not improve despite 2weeks of amoxicillin treatment followed by 2 weeks of cephalexin treatment. An X-ray suggested osteoar-thritis. After 2 months without improvement, an orthopedist in-jected a corticosteroid, with temporary improvement of the swell-ing and erythema. However, the swelling subsequently recurred, and magnetic resonance imaging (MRI) revealed moderate teno-synovitis of the flexor tendon. She underwent operative irrigation and debridement, and marked edema without purulence wa