Severe late‐onset neutropenia induced by ocrelizumab in a multiple sclerosis patient: A case report

Ocrelizumab is a recombinant humanized antibody targeted against CD‐20 molecule, which was approved for the treatment of relapsing and primary progressive multiple sclerosis. Common adverse events of ocrelizumab include infusion‐related reactions like rash, pruritus, and flushing. Late‐onset neutropenia (LON) is a rarely reported complication of ocrelizumab therapy. We report a case of severe late‐onset neutropenia in a patient with primary progressive multiple sclerosis treated with ocrelizumab with neutropenia occurring 3 months after the last dose received treated with empirical broad‐spectrum intravenous antibiotics and filgrastim. Severe late‐onset neutropenia is a rare unpredictable adverse event and outlines the importance of regular routine blood workup for detecting severe neutropenia early in its course.