Successful Rituximab Therapy in IgG4-Related Sclerosing Mesenteritis

Immunoglobulin G4-related disease (IgG4-RD) is an increasingly common autoimmune, multiorgan fibro-inflammatory disorder. Its involvement of organs like the pancreas, lacrimal glands, salivary glands and kidneys is well known but IgG4RD presenting as sclerosing mesenteritis is a rare entity. On imaging, it presents as a mesenteric mass and biopsy is the gold standard for confirmation as elevated serum IgG4 levels are unreliable to establish the diagnosis. Here we report a previously healthy 33-year-old African American female who presented with one week history of generalized abdominal pain. Imaging studies revealed a mass within the mesentery and post-operative biopsy of the mass confirmed the presence of mesenteric fibrosis and obliterative phlebitis. Interestingly her serum IgG4 levels were normal but an elevated IgG4/IgG ratio of >40% was noted on biopsy specimen, consistent with the diagnosis of IgG4 related sclerosing mesenteritis. Following the surgery, the patient had a recurrence in symptoms for which she was treated with steroids and rituximab. This case highlights the diagnostic challenges and variability of IgG4RD, as serum IgG4 levels are not always elevated in sclerosing mesenteritis. Rituximab, a B-cell depleting agent, is well-established for treating IgG4-related diseases, but its role in IgG4-related sclerosing mesenteritis is less clear. While Rituximab has been shown to reduce serum IgG4 levels and improve clinical symptoms in many patients, its effectiveness in mesenteritis specifically remains understudied. Our patient showed clinical and laboratory resolution with rituximab, suggesting its potential role in managing relapses or steroid-resistant cases. Further studies are needed to better define rituximabs role in the treatment of IgG4-related sclerosing mesenteritis.