RT Journal Article SR Electronic T1 Refractory Mycobacterium genavense infection secondary to thymoma-associated endogenous IL-12 inhibitor JF BMJ Neurology Open JO BMJ Neurol Open FD BMJ Publishing Group Ltd SP e000285 DO 10.1136/bmjno-2022-000285 VO 4 IS 1 A1 Jessie Chen A1 MaiAnh Nguyen A1 Hannah Hu A1 Elaine Cheong A1 D Sean Riminton A1 Stephen Reddel YR 2022 UL http://neurologyopen.bmj.com/content/4/1/e000285.abstract AB Case A 39-year-old man with thymoma-associated acetylcholine receptor antibody myasthenia gravis (MG) presented with fevers, night sweats, abdominal pain and weight loss. Marked splenomegaly and intra-abdominal lymphadenopathy were found. Biopsies confirmed disseminated Mycobacterium genavense infection. Despite antimicrobials and reduced immunosuppressive medications, he worsened. We suspected a thymoma-associated cytokine inhibitory antibody. The addition of subcutaneous interferon-gamma (IFN-γ) induced clinical and radiological improvement. His antimicrobials were able to be ceased. MG remained stable. Subsequent testing demonstrated an endogenous interleukin-12 (IL-12) inhibitor, likely inhibiting the IL-12/IFN-γ axis crucial for defence against mycobacterial infections.Discussion This case illustrates the autoimmune manifestations that can occur with thymoma. It illustrates the benefit of exogenous IFN-γ in overcoming the immune deficit. In this case, its use did not exacerbate existing autoimmune disease or trigger others. We raise awareness of the need to consider cytokine pathway defects as a contributing factor to refractory atypical infections in patients with thymoma-associated MG.Data are available upon reasonable request.