Infection with Mycobacterium haemophilum, a rare, slow-growing organism, most commonly presents as ulcerating cutaneous lesions and subcutaneous nodules in immunocompromised adults.1 The most common clinical presentation in adults includes cutaneous lesions, nodules, cysts, and papules, with signs and symptoms of erythema, pain, pruritus, and drainage.2 Disseminated disease states of septic arthritis, pulmonary infiltration, and osteomyelitis, though life-threatening, are less common manifestations reported in highly immunocompromised persons.3
Infection with M haemophilum presents a challenge to the dermatology community because it is infrequently suspected and misidentified, resulting in delayed diagnosis. Additionally, M haemophilum is an extremely fastidious organism that requires heme-supplemented culture media and a carefully regulated low temperature for many consecutive weeks to yield valid culture results.1 These features contribute to complications and delays in diagnosis of an already overlooked source of infection.
We discuss the clinical presentation, diagnosis, and treatment of 3 unusual cases of cutaneous M haemophilum infection involving the upper arms. The findings in these cases highlight the challenges inherent in diagnosis as well as the obstacles that arise in providing effective, long-term treatment of this infection.
A 69-year-old woman with a medical history of a single functioning kidney and moderate psoriasis managed with low-dosage methotrexate presented with an erythematous nonhealing wound on the left forearm that developed after she was scratched by a dog. The pustules, appearing as bright red, tender, warm abscesses, had been present for 3 months and were distributed on the left proximal and distal dorsal forearm (Figure 1A). The patient reported no recent travel, sick contacts, allergies, or new medications.
A shave biopsy was initially obtained. Swab specimens were sent for bacterial, fungal, and mycobacterial culture following discontinuation of methotrexate. Initial histopathologic analysis revealed aggregates of histiocytes and multinucleated giant cells within the dermis, surrounded by infiltrates of lymphocytes and neutrophils (Figure 2), consistent with a dermal noncaseating granulomatosis. Acid-fast bacilli (AFB), periodic acid–Schiff, Gram, and Grocott-Gomori methenamine-silver stains were negative for pathogenic microorganisms. There was no evidence of vasculitis.