A Case of Atypical Mycobacterial Infection in a Patient with Bechet's Disease

Abstract

Background: Although Mycobacterium chelonae is ubiquitously found in the environment, cutaneous infections with M. chelonae are rarely reported. The few reported cases generally feature opportunistic infections in immunocompromised hosts. Due to its uncommon nature, providers often overlook this mycobacterium as the causative agent of a painful erythematous rash in their differential diagnosis. This case highlights common presentations and features of M. chelonae infection and demonstrates the importance of looking to ordinarily benign organisms as harmful and virulent in our immunocompromised population. Case Presentation: A 48-year-old female with refractory Behçet’s disease, maintained on methylprednisolone and apremilast, presented for a painful rash on her left lower extremity. She reported two months of tender nodules spreading from her ankle up to her medial thigh. Exam revealed erythematous and violaceous nodules in a sporotrichoid pattern. Three skin biopsies were performed over a period of two months; the first two were inconclusive, while the third showed marked dermal and subcutaneous inflammation with microabscess formation. Fite and AFB stains highlighted acid fast organisms. Subsequent acid-fast bacilli tissue culture grew M. chelonae. The patient was initiated on triple antibiotic therapy with tobramycin, linezolid, and clarithromycin; however, her course was complicated by drug-induced liver injury. She was then transitioned to tobramycin and imipenem, leading to acute kidney injury and rhabdomyolysis. This prompted a final shift to imipenem and omadacycline, which was ultimately successful in resolving the rash. Discussion: Although cutaneous infections with M. chelonae and other atypical mycobacteria are rare, providers should maintain a high level of suspicion in immunocompromised patients presenting with skin lesions, especially in a sporotrichoid pattern. Violaceous nodules in immunocompromised hosts should always warrant an infectious work-up. The diagnosis of atypical mycobacterial cutaneous infections in a timely fashion may be challenging. Multiple representative biopsies may be required for histopathological examination, which should include acid-fast staining, followed by routine bacterial and mycobacterial culture to achieve the most accurate diagnosis.