Rare coexistence of X-linked hyper immunoglobulin M syndrome and polyarticular juvenile idiopathic arthritis in a Chinese child: A case report.

Immune dysregulation in children can lead to a variety of health issues, including infections, allergies and autoimmune diseases. However, the coexistence of autoimmune diseases and primary immunodeficiency disorders is extremely rare in clinical practice. A 4-year-old male patient was admitted in July 2017 with joint swelling and pain, alongside a history of recurrent respiratory infections and severe pneumonia. Physical examination revealed tenderness and swelling in multiple joints, and laboratory tests indicated elevated inflammatory markers. Imaging studies showed joint effusion and inflammatory lesions in the lungs. He was diagnosed with rheumatoid factor-negative polyarticular juvenile idiopathic arthritis (PJIA) and treatment was initiated with naproxen, methotrexate and etanercept, leading to significant symptom improvement. In July 2019, following a decline in immunoglobulin (Ig) M (IgM) levels (IgM 0.36 g/L) and recurrent infections, genetic testing was conducted, revealing a frameshift mutation in the CD40LG gene (c.621dup A, p.A208Sfs * 23), which confirmed the diagnosis of X-linked hyper IgM syndrome (XHIGM). The treatment regimen was adjusted to include monthly intravenous Ig infusions and prophylactic antibiotics, significantly reducing the frequency of respiratory infections. By January 2021, PJIA was in clinical remission, allowing for the discontinuation of immunosuppressive therapy, with follow-ups indicating continued recovery without discomfort. In conclusion, this case underscores the rare coexistence of XHIGM and PJIA in the field of pediatrics and identified a new pathogenic variant in CD40LG, enhancing our understanding of the clinical management of individuals with concurrent autoimmune and immunodeficiency disorders.