BackgroundTumor necrosis factor antagonist inhibitors have transformed the approach to patients with severe autoimmune conditions, such as rheumatoid arthritis. Although the therapy can be highly effective, TNF-α inhibitors are associated with an increased risk of opportunistic infections.Case presentationHere, we report a case of concomitant disseminated histoplasmosis and tuberculosis in a 65-year-old female with rheumatoid arthritis treated with TNF-α inhibitor. Both conditions can be found in disseminated form in immunosuppressed hosts, but co-infection is rare with only a few cases having been reported, to our knowledge, all in HIV patients.ConclusionsThis case posed a considerable challenge for diagnosis and treatment due to the unusual disseminated co-infection, the overlapping symptoms, and the interactions between medications.