Mycobacterial lymphadenitis without granuloma formation in a patient with anti-interferon-gamma antibodies

A previously healthy 49-year-old Japanese woman presented with cervical lymph node swelling and tenderness. Lymph node biopsy revealed reactive lymphadenitis without granulomas. No malignant cells were found, and no acid-fast positive bacilli were identified by Ziehl-Neelsen staining. She was treated unsuccessfully with various antibiotics, and it was very challenging to reach a diagnosis. ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) uptake in bones was evaluated using positron emission tomography-computed tomography (PET-CT), and disseminated mycobacterial infection was suspected. The interferon-gamma (IFN-γ) release assays QuantiFERON (QFT) and T-SPOT were used to diagnose tuberculosis infection. On testing, a difference in mitogen response was found between these assays. The response was low for QFT but adequate for T-SPOT, suggesting the presence of anti-IFN-γ antibodies. This difference depended on whether the patient's plasma (including anti-IFN-γ antibodies) was used within the assay system. Mycobacterium abscessus was isolated from lymph node cultures, and plasma anti-IFN-γ antibodies were confirmed. The patient was diagnosed with disseminated M. abscessus infection with underlying adult-onset immunodeficiency caused by anti-IFN-γ antibodies. Granulomas are a pathological hallmark of mycobacterial infection, but may not fully form in immunodeficient patients. Clinicians should be aware of the possibility of mycobacterial infection without granuloma formation due to anti-IFN-γ antibodies.