A patient with positive anti‐<scp>IFN</scp>‐γ autoantibody and monoclonal gammaglobulinemia masquerading as multiple myeloma: Case report and literature review

Adult-onset immunodeficiency (AOID) is an emerging acquired immunodeficiency due to anti-IFN-γ autoantibody (AIGA) with low morbidity, frequent disseminated infections, a prolonged course, difficult diagnosis and treatment, and a poor prognosis. Here, we report a patient with positive AIGA and monoclonal gammaglobulinemia who was mimicking symptomatic multiple myeloma and resulting in a non-tuberculous mycobacterial (NTM) infection. While he achieved an excellent therapeutic effect with anti-plasma cell therapy, it also serves as a warning that monoclonal gammaglobulinemia with NTM infection is easily misdiagnosed as symptomatic multiple myeloma, and the screening for AIGA should not be ignored in patients with NTM infection.