Bacillus Calmette–Guérin (BCG)‐associated hemophagocytic lymphohistiocytosis in the setting of IFN‐γR1 deficiency: A diagnostic dilemma

Hemophagocytic lymphohistiocytosis (HLH) disease is a severe immune dysregulation caused by mutations in genes required for lymphocyte cytotoxicity function. However, HLH‐like syndrome may develop secondary to infections, malignancy, and autoimmunity. Primary immunodeficiencies (PIDs) could predispose to HLH syndrome after uncontrolled infections. Mendelian susceptibility to mycobacterial disease (MSMD) is a PID characterized by a predisposition to clinical disease caused by weakly virulent mycobacteria, such as bacillus Calmette–Guérin (BCG). Inborn errors of interferon‐γ immunity caused by mutations in 16 genes, underly MSMD development. Here, we report a case of fatal interferon‐γ receptor 1 deficiency with disseminated BCG infection, which was initially diagnosed with HLH disease. We also include a review of cases reported in the literature.