Rapid-onset massive immune-mediated pericardial effusion in a patient with anti-IFN-γ autoantibodies syndrome.

BACKGROUND: Anti-interferon-gamma (IFN-γ) autoantibodies (AIGAs) syndrome is an emerging adult-onset immunodeficiency (AOID) associated with opportunistic infections and immune dysregulation. Pericardial effusion as a direct manifestation of this syndrome is rarely reported. CASE PRESENTATION: A 46-year-old man with a history of Talaromyces marneffei (TM) infection and clinically suspected pulmonary nontuberculous mycobacterial (NTM) disease presented with rapid-onset massive pericardial effusion. The NTM diagnosis was not microbiologically confirmed, as the patient declined bronchoscopy. Pericardial fluid analysis revealed a high inflammatory cell count and an anti-IFN-γ autoantibody titer of 1:2500, identical to serum, despite a negative microbiological workup and no definitive evidence of malignancy on available cytological evaluation. The patient responded well to corticosteroids and anti-NTM therapy, with complete resolution of effusion. CONCLUSION: This case highlights pericardial effusion as a potential immune-mediated complication of AIGAs syndrome. Clinicians should consider this diagnosis in patients with unexplained serositis and a history of opportunistic infections.