A case of granulomatous lymphocytic interstitial lung disease considered as sarcoidosis

Inborn errors of immunity (IEI), formerly referred to as primary immunodeficiency disorders, comprise ten groups and more than 500 distinct diseases. Common variable immunodeficiency (CVID) is the most prevalent symptomatic IEI in adults and is characterised by reduced immunoglobulin levels and recurrent infections after exclusion of secondary causes of hypogammaglobulinaemia. Granulomatous lymphocytic interstitial lung disease (GLILD) is a distinct clinical entity associated with CVID, defined by lymphoid proliferation and granuloma formation within the lung interstitium. GLILD shares numerous clinical, radiological, and pathological similarities with sarcoidosis; however, hypogammaglobulinaemia, indicative of immunodeficiency, is rarely encountered in sarcoidosis. To present a case initially diagnosed as sarcoidosis, in whom hypogammaglobulinaemia detected during follow-up led to the final diagnosis of primary immunodeficiency with granulomatous lymphocytic interstitial lung disease. This case report retrospectively reviews the patient’s clinical course, laboratory data, radiological findings, and histopathological results. Following the detection of hypogammaglobulinaemia, comprehensive immunological evaluation was performed, confirming the diagnosis of primary immunodeficiency. GLILD can closely mimic sarcoidosis in clinical, radiological, and pathological aspects. The presence of hypogammaglobulinaemia should prompt consideration of underlying primary immunodeficiency. This case highlights the importance of immunological assessment in patients with granulomatous interstitial lung disease to ensure accurate diagnosis and appropriate management.