Twelve cases are reported in which tendon sheaths, joints, bursae, or soft tissue were infected with unclassified species of mycobacteria other than Mycobacterium tuberculosis. The subchondral bone of the femur was involved in one, and the subcutaneous soft tissue alone in one case.

The organism or organisms causing the infections are culturally different from Mycobacterium tuberculosis var. hominis or var. bovis. They are not Mycobacterium avium, Mycobacterium balnei, or Mycobacterium ulcerans. They are not virulent for guinea pigs in the usual sense. They would appear to belong to a large group of organisms some of which are recognized as pathogens in the lungs. In addition, they are usually insensitive to para-aminosalicylic acid, isonicotinic acid hydrazide, and streptomycin, even though the infection has not been previously treated with these agents. Pathologically, they produce granulomata that are quite similar microscopically to those of tuberculosis or brucellosis.

Operative incisions, accidental puncture wounds or those resulting from injections, and small lacerating wounds may represent the mode of entry of the organisms. Pre-existing rheumatoid arthritis may be a factor in allowing the proper host-invader relationship to exist, or this factor may he coincidental with the intra-articular injections that rheumatoid patients often receive.

Accurate diagnosis is dependent on close cooperation of surgeon, surgical pathologist, and microbiologist. Treatment is of necessity surgical, with reliance on adequate excision of diseased tissue. Antibacterials are not helpful in most instances because of insensitivity of the organisms to drugs.