A Rare Infection in a Patient with Systemic Lupus Erythematosus Treated with Mycophenolate Mofetil

Mycobacterium haemophilum is a very rare and slow-growing nontuberculous mycobacteria that affects mainly immunocompromised patients. Only 250 cases have been reported in the literature since its discovery in 1978. We report a case of a 69-year-old female with systemic lupus erythematosus and lupus nephritis on mycophenolate mofetil who presented with worsening skin nodules. The presence of lower limb edema and proteinuria further confounds the clinical picture toward a lupus flare. Despite treatment for a lupus flare, she developed high-grade fever and new skin nodules, posing a clinical dilemma. She had multiple subcutaneous nodules with ecchymosis along the bilateral thighs and dorsum of the left hand down to the left index finger and along the ulnar aspect of the left wrist, without periungual erythema. Skin biopsy revealed granulomatous inflammation with numerous acid-fast bacilli. The organism was subsequently identified as M. haemophilum by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Clinicians should have a low threshold for suspicion of mycobacterial infection and their cutaneous manifestations in immunocompromised patients. Failure to respond to usual treatments should trigger a skin biopsy in a timely manner. New bacterial identification techniques such as gene sequencing and MALDI-TOF are very useful to identify fastidious organisms and to plot appropriate treatment.