The histopathology of Mycobacterium marinum synovitis.

Eight patients with culture-proven Mycobacterium marinum synovitis had synovial specimens with a remarkably similar histologic appearance. There was considerable synovial hyperplasia, and the synovium was thickened by a moderately intense lymphohistiocytic infiltrate, notably devoid of plasma cells. Fibrin covered some synovial surfaces. Giant cells were both of the Langerhans' and foreign body types. Granulomas were noncaseating but varied in frequency and degree of definition. Knowledge of this morphologic picture has proved to be useful in patient care.