Mycobacterial panniculitis caused by Mycobacterium thermoresistibile in a cat

CASE SUMMARY: A domestic shorthair cat was evaluated for chronic, bilateral, ulcerative dermatitis affecting the inguinal region and lateral aspects of both pelvic limbs. Histopathologic examination of skin biopsies collected throughout the course of disease revealed chronic pyogranulomatous ulcerative dermatitis. Aerobic bacterial skin cultures yielded growth of a methicillin-resistant Staphylococcus aureus and Corynebacterium amycolatum. Upon referral the clinical findings were suggestive of a non-tuberculous Mycobacterium species infection. Previously obtained skin cultures failed to yield growth of mycobacterial organisms. A deep skin biopsy was collected and submitted for mycobacterial culture. At 5 weeks of incubation Mycobacterium thermoresistibile was isolated. In previous reports, M thermoresistibile has been isolated after 2–4 days of incubation, suggesting that this strain may have been a slower growing variant, or other factors (such as prior antimicrobial therapy) inhibited rapid growth of this isolate. The cat was hospitalized for intravenous antibiotic therapy, surgical debridement of wounds, vacuum-assisted wound closure therapy and reconstruction procedures. The wounds were ultimately primarily closed and the cat was discharged to the owner after 50 days of hospitalization. Seven months after hospitalization, the ulcerative skin lesions had healed. RELEVANCE AND NOVEL INFORMATION: To our knowledge, only two cases of M thermoresistibile panniculitis have been reported in cats. In the only detailed report of feline M thermoresistibile panniculitis, treatment was not attempted. The second case only reported detection of M thermoresistibile by PCR without a clinical description of the case. In our case report, severe chronic skin infection with M thermoresistibile was addressed using prolonged specific antibiotic therapy, surgical debridement and reconstructions, and treatment of secondary bacterial infections.