Case Presentation:  A 32-year-old man with human immunodeficiency virus (HIV) presented with a painful and swollen right ankle. The patient had been well until 6 weeks ago when he developed a sprain followed by worsening pain and swelling of his ankle. His CD4+ T-lymphocyte count was 169 cells/mm3 with a viral load of 3770 copies/mL. His treatment regimen consisted of darunavir, ritonavir, emtricitabine, tenofovir and atovaquone. Patient has never travelled outside of Texas. He worked as a waiter and lived with his sister, who had 2 dogs that were recently infested with fleas. He stated having multiple male partners and using condoms intermittently in the past, however, he remained abstinent since his HIV diagnosis 6 years ago. Pertinent exam findings were a slight fever to 38.2°C, mild tachycardia to 102, and pale mucous membranes and conjunctivae. His right ankle had 2+ edema, erythema, and was tender to active and passive motion. Radiographs of the right ankle showed a permeative bone lesion in the distal right tibial metadiaphysis with cortical osteolysis and periosteal reaction. MRI was consistent with extensive osteomyelitis of the right distal tibia and the additionally the distal fibula. Septic right tibiotalar joints with extensive synovitis and necrotic tissue/fluid extending from the bone into the surrounding soft tissues was also noted. Arthrocentesis revealed turbid synovial fluid with 20,900 white blood cells/microL. Bartonella, bacterial, fungal and acid-fast bacilli (AFB) stains and cultures cultures were obtained. Empiric intravenous vancomycin and piperacillin/tazobactam and fluid resuscitation were initiated. Despite therapy, his symptoms persisted. In the following days, his synovial fluid AFB stain was reported as positive and he was switched to rifabutin, clarithromycin and ethambutol. Cultures revealed mycobacterium avium-intracellulare complex (MAC). Surgery was consulted and recommended extensive debridement with potential below the knee amputation, however, patient opted for medical management.

Discussion: MAC is a common opportunistic entity responsible for disseminated infection in advanced AIDS, but rarely manifests as osteomyelitis. A thorough literature review suggests that MAC osteomyelitis tends to occur in patients receiving HAART therapy with CD4+ counts >100 cells/µL, which hints towards a possible relation to immune reconstitution inflammatory syndrome. Furthermore, MAC osteomyelitis often develops late in AIDS patients, involving multiple sites of the bones, with the hip and vertebrae being common niduses. Our patient, although having an appropriate CD4+ count, was found to have MAC osteomyelitis and septic arthritis in his distal right leg, an uncommon location for MAC to attack. 

Conclusions:  Given the devastating complications of osteomyelitis in HIV patients, physicians must maintain a high degree of suspicion for opportunistic entities such as MAC, despite their uncommon occurrence.