An Interesting Case of Immunoglobulin G4-Related Retroperitoneal Fibrosis Treated With Rituximab

Immunoglobulin G4-related disease (IgG4-RD) is a fibroinflammatory condition. Its common manifestations include type I autoimmune pancreatitis and retroperitoneal fibrosis (RPF). We present a rare case involving a 43-year-old female who presented with left lower quadrant (LLQ) pain. Imaging of the abdomen and pelvis revealed left hydroureteronephrosis to the level of an inflammatory process in the left adnexal region, possibly reflecting a tubo-ovarian abscess (TOA). The gynecologic evaluation concluded that the mass was unlikely of gynecologic sources. Transgluteal biopsy of the mass was highly suggestive of IgG4-RD. The patient received prednisone and rituximab (RTX), resulting in complete resolution of the mass, which was confirmed on repeat imaging. This case report provides a valuable addition to the literature to highlight that the diagnosis of IgG4-RD is based on the combination of characteristic clinical, serologic, radiologic, and histopathologic findings. Also, it underlines that the management of the disease is through glucocorticoids (GCs) as the first-line agent for remission induction in all patients with active, untreated IgG4-RD. RTX therapy is an effective treatment for IgG4-RD that is refractory to GCs. Recent studies have suggested that RTX monotherapy can be used to induce and maintain remission in patients with IgG4-RD.