Granulomatous Lymphocytic Interstitial Lung Disease as the Initial Manifestation of Common Variable Immunodeficiency in a Young Adult

Common variable immunodeficiency (CVID) is a primary immunodeficiency that often goes unrecognized until adolescence or adulthood. Granulomatous-lymphocytic interstitial lung disease (GLILD) is a non-infectious pulmonary complication of CVID that can be subtle, sometimes presenting before significant infections or systemic symptoms. A 19-year-old female patient presented with mild flu-like symptoms. Examination revealed splenomegaly, and routine labs showed mild anaemia and thrombocytopenia. Despite rapid recovery from influenza A, persistent splenomegaly prompted further evaluation. Chest CT demonstrated multiple nodules, ground-glass opacities, and mediastinal lymphadenopathy, findings surprisingly disproportionate to her mild symptoms. Her history of recurrent childhood infections, combined with marked hypogammaglobulinemia and abnormal B-cell immunophenotyping (including increased CD21^low B cells), raised suspicion for CVID. Lung biopsy confirmed GLILD. She was started on immunoglobulin replacement therapy, and at follow-up, her pulmonary lesions remained stable with no new infections. This case highlights how CVID can present subtly, with imaging findings that far exceed the apparent clinical severity. GLILD may be the first clue to an underlying immunodeficiency, emphasizing the importance of a detailed history, immunologic testing, and histopathologic confirmation. Timely recognition allows for early initiation of therapy and close monitoring, potentially improving long-term outcomes. Even mild respiratory symptoms may mask serious underlying immune dysregulation. Clinicians should consider primary immunodeficiencies like CVID in young adults when imaging or lab findings are inconsistent with common infections, as early diagnosis can significantly impact management and prognosis.