Mycobacterium kansasii osteomyelitis presenting as a solitary lytic lesion of the ulna: fine-needle aspiration findings and morphologic comparison with other mycobacteria.

A 35-yr-old woman, with acquired immunodeficiency syndrome, presented with right arm pain, erythema, and swelling. A lytic lesion of the ulna was found by radiograph. Ultrasonic and fluoroscopic guided fine-needle aspiration (FNA) yielded a neutrophilic and histiocytic exudate admixed with abundant long, bacillary forms that appeared as negative images on Papanicolaou stain and as very coarsely beaded acid-fast bacilli, resembling candy canes, on Kinyoun stain. These morphologic features permitted a preliminary diagnosis of mycobacteriosis, possibly of M. kansasii (MK) etiology. Appropriate therapy was initiated and resulted in not only marked symptomatic improvement of osteomyelitis and cellulitis, but resolution of chronic pulmonary infiltrates, presumed to be caused by fibrosis. Culture confirmed MK infection 3 wk after FNA. MK is one of the few mycobacteria that has a sufficiently characteristic morphology to permit presumptive diagnosis by smear. Culture, however, still remains the definitive method of speciation.