• atypical mycobacteria;
  • infectious diseases;
  • molecular pathology

The case of a 66-year-old female who developed sudden redness and swelling of her left thumb is presented. A biopsy showed well formed granulomas, mixed inflammation with a predominance of neutrophils, and acid-fast bacilli. After negative culture results, tissue was sent for a broad-range polymerase chain reaction amplification followed by suspension array identification, which classified the pathogenic organism as Mycobacterium avium-intracellulare. The patient was started on clarithromycin, rifabutin and ethambutol leading to clinical improvement. M. avium-intracellulare is present in soil, fresh water, sea water, dairy products and some animal tissues. Primary cutaneous manifestations are uncommon in the immunocompetent host. As cultures may be negative or can take up to three weeks to show growth, the molecular approach described here offers an opportunity for more rapid and specific diagnosis.