BCG arthritis in a patient with Severe Combined Immunodeficiency Disorder (SCID): a case report

Severe combined immunodeficiency (SCID) is a rare group of primary immunodeficiency disorders characterized by profound defects primarily in T cells and, in certain subtypes, in B and NK cells as well. These immune deficiencies predispose affected patients to life-threatening infections and complicate their clinical management. Since the BCG vaccine is routinely administered to neonates in most countries, undiagnosed SCID patients face a significant risk of developing severe localized or disseminated BCG-related complications. Therefore, it should be taken into account in suspicious populations. The patient was a 16-month-old Iranian male with JAK3 gene mutation-associated SCID who presented with progressive left elbow swelling, pain, and restricted mobility over 10 days. Physical examination revealed tachycardia, fever, marked swelling and tenderness with severely restricted range of motion, and a firm, fixed, warm palpable mass. Soft tissue ultrasound demonstrated moderate joint effusion with synovial thickening, multiple irregular hypoechoic areas, and increased Doppler vascularity consistent with chronic monoarthritis and periarticular masses of probable bacterial origin. Given the lack of response to empirical therapy and conservative management, surgical excision was performed. Histopathological examination revealed neoplastic spindle cell proliferation with hyperchromatic nuclei, epithelioid macrophages, mixed inflammatory infiltrate, and numerous acid-fast bacilli both intracellularly and extracellularly. To reliably distinguish BCG from other members of the Mycobacterium tuberculosis complex, molecular analysis was performed, which demonstrated deletion of the RD1 region, confirming BCG arthritis. Following surgery and antimycobacterial therapy, the patient demonstrated marked clinical improvement, particularly in elbow range of motion, and was discharged after completing intravenous antibiotics and achieving clinical stabilization. This case underscores the critical need for revised immunization policies in TB-endemic countries, implementation of systematic neonatal primary immunodeficiency screening programs such as TREC screening, and enhanced healthcare provider awareness regarding the potentially catastrophic consequences of BCG vaccination in immunocompromised populations.