Objective:

Background:

Neutropenic enterocolitis (NEC), historically referred to as typhlitis, is a heterogenous condition characterized by fever and abdominal pain in the setting of neutropenia (absolute neutrophil count [ANC] <1,500 mm3).  Early reports of NEC were in children undergoing chemotherapy for leukemia or lymphoma. The etiology of NEC is multifactorial, due to intestinal mucosal injury, neutropenia, and impaired defense against gastrointestinal microorganisms. While occurring most often in the cecum, NEC may involve any segment of the GI tact, including the small intestine, appendix, and colon. Ocrelizumab is a disease modifying therapy used for treatment of multiple sclerosis (MS), which works through CD20-antibody targeted depletion of B-lymphocytes, but not neutrophils. Case reports of ocrelizumab-induced late-onset neutropenia (LON) have proposed lymphocyte repopulation occurring at the expense of granulocyte and neutrophil synthesis as a possible cause.  Reports of ocrelizumab-induced colitis are also emerging; the etiology remains unclear but are thought to be related to immunological dysregulation.

Design/Methods:

N/A

Results:

We present a 26-year-old man who was diagnosed with multiple sclerosis and started on Ocrelizumab in May 2022. In December 2022, he developed painful cough, and would go on to experience fever, sore throat, and emesis. He was found to have neutropenia (ANC 1390 mm3). CT of chest abdomen and pelvis was unremarkable. Blood cultures and cerebrospinal fluid cultures were unrevealing. Given unexplained neutropenia, abdominal pain, and bloody stool, CT of the abdomen was repeated and revealed sigmoid colitis.

Conclusions:

To our knowledge, there are no reported cases of NEC after treatment with Ocrelizumab.  LON is a rare side effect of Ocrelizumab, and our case suggests typhlitis as a potential etiology in patients exposed to Ocrelizumab. Our case highlights the importance of considering infectious colitis in Ocrelizumab-exposed patients who develop neutropenia.