Crohn's disease following rituximab treatment in a patient with refractory nephrotic syndrome.

Rituximab (RTX) is increasingly used for the treatment of refractory nephrotic syndrome due to its inhibitory effect on B cells which extends the period of remission, while lowering the dose of steroids needed for disease management. However, RTX can lead to various side effects, including Crohn's disease. Herein, we describe a case of a 15-year-old boy with refractory nephrotic syndrome diagnosed at age 9 years who developed Crohn's disease following RTX treatment. RTX was initiated in this patient at the age of 13 years 6 months due to occurrence of 12 relapses of nephrotic syndrome over a 4-year period, despite treatment using cyclosporine, steroid pulse therapy, and mycophenolate mofetil. The patient received 4 doses of RTX over a 2-year period (dose, 375 mg/m2). Although the treatment was effective in extending the disease-free duration up to 6 months, at the age of 15 years 9 months, the patient developed abdominal pain, associated with frequent watery stools and rapid weight loss. Based on clinical and endoscopic findings, he was diagnosed with Crohn's disease and treated using infliximab. Remission of Crohn's disease was achieved with this treatment, with no further relapse of nephrotic syndrome. Infliximab is thought to extend the remission period of nephrotic syndrome. In this case, we propose that Crohn's disease was caused by an abnormal immune tolerance, secondary to the use of RTX, although the exact underlying mechanism remains to be clarified. Therefore, inflammatory bowel disease should be considered if severe abdominal symptoms with weight loss following RTX administration are observed.