Mycobacterium avium Brain Abscess in a 45 year-old Male with HIV-Induced Immune Reconstitution Inflammatory Syndrome (IRIS)

Abstract Background: The Mycobacterium avium-intracellulare complex (MAC) consists of two mycobacterial species- M.avium and M. intracellulare . The organisms exist in nature in water, soil, and food and can be acquired via inhalation or ingestion. It is an uncommon cause of infection, initially affecting the pulmonary system in patients with underlying lung disease or immunocompromised patients. Extra-pulmonary infection can occur in the liver, spleen, skin, soft tissue, and lymph nodes. Only ten cases in the English literature have documented central nervous system (CNS) infections. Additionally, these eight cases were reported in HIV positive patients who presented with single or multiple enhancing brain lesions and were initially misdiagnosed as toxoplasmosis. Case presentation: We report a case of a 45-year-old male who was diagnosed with HIV/ AIDS and was found to have four parietal and temporal ring-enhancing lesions by MRI that failed to improve on anti-Toxoplasmosis therapy. A brain biopsy demonstrated multiple nodular granulomata with lymphoplasmacytic cells, epithelioid histiocytes, and rare giant cells. No caseous necrosis is seen, but foci of micronecrosis were present. No toxoplasmosis or primary CNS lymphoma was present. Very abundant acid-fast bacilli were seen on Fite and auramine stains. In addition, there was heavy CD8 + T cell infiltration suggestive of Immune Reconstitution Inflammatory Syndrome (IRIS). PCR and sequencing of paraffin-embedded brain tissue demonstrated M. avium . He was treated with Rifampin, Isoniazid, Pyrazinamide and Ethambutol (RIPE) plus clarithromycin 500 mg BID that was switched to azithromycin 500 mg to decrease QTc prolongation. He is also now on anti-retroviral therapy. At the last clinic visit approximately five months after diagnosis of CNS MAC, he was very much improved.Conclusion: Brain MAC abscess is very rare, with less than 10 cases being previously reported in both AIDS and non-AIDS patients. This diagnosis should be considered in immunocompromised patients who do not respond to anti-toxoplasmosis therapy and brain biopsy is important to provide definitive identification and guide treatment.