Multifocal Cutaneous and Musculoskeletal Mycobacterium haemophilum Infection Mimicking Erythema Nodosum and Crystal Arthropathy in a Kidney Transplant Recipient: A Case Report.

BACKGROUND: Mycobacterium haemophilum is an uncommon nontuberculous mycobacterium that primarily affects immunocompromised hosts and may present with cutaneous and musculoskeletal manifestations that mimic inflammatory or infectious disorders. Its specialized growth requirements often delay diagnosis, particularly in solid organ transplant recipients.

CASE PRESENTATION: A 59-year-old man with a history of deceased donor kidney transplantation presented with progressive bilateral ankle pain, lower extremity swelling, and painful nodular skin lesions. Initial evaluation suggested erythema nodosum and inflammatory arthritis, with nondiagnostic musculoskeletal imaging and arthrocentesis. Corticosteroid therapy resulted in only transient improvement. Persistent low-titer serum cryptococcal antigenemia with negative cerebrospinal fluid studies further complicated the diagnostic evaluation and prompted empiric fluconazole therapy. Progressive disease led to recurrent hospitalization and inability to bear weight. Initial synovial fluid aspiration demonstrated acid-fast bacilli, whereas repeat bilateral aspirations demonstrated concomitant monosodium urate crystals and acid-fast bacilli. Skin biopsy demonstrated rod-shaped acid-fast organisms with negative fungal staining. Routine cultures were unrevealing, but independent polymerase chain reaction testing performed at two reference laboratories identified M. haemophilum. Mycophenolate mofetil was withheld because of active infection, whereas tacrolimus therapy was continued with therapeutic drug monitoring. Prolonged multidrug antimicrobial therapy was individualized according to susceptibility testing and medication tolerance. Despite treatment-related complications, the patient experienced substantial clinical improvement with healing of cutaneous lesions, restoration of mobility, and preservation of kidney allograft function.

CONCLUSION: This case highlights the diagnostic complexity of M. haemophilum infection in kidney transplant recipients. Simultaneous erythema nodosum-like lesions, crystal arthropathy, and persistent serum cryptococcal antigenemia obscured the diagnosis, whereas conventional microbiologic studies remained largely unrevealing. Early consideration of opportunistic nontuberculous mycobacterial infection and the use of molecular diagnostics may facilitate timely diagnosis and appropriate management in immunocompromised patients.