Ocrelizumab is a humanized monoclonal anti-CD20 antibody approved for treatment of relapsing-remitting and primary progressive multiple sclerosis (MS). Before approval of this drug, the chimeric anti-CD20 antibody rituximab was used off-label for treatment of MS. On treatment with rituximab late-onset neutropenia (LON) was reported as a rare adverse event primarily in rheumatologic patients.
So far, only two patients developing LON on treatment with ocrelizumab were reported leaving open the question about potential underlying mechanisms. By reporting a case of LON in a patient treated first with rituximab followed by ocrelizumab, we aim to raise awareness to this rare, but potentially threatening adverse event.
Here we report the case of a 21 years old female caucasian patient with highly active relapsing-remitting multiple sclerosis, who experienced LON after first dose ocrelizumab switched from rituximab.
Our patient was first treated with two cycles rituximab in a dosage of 375 mg/m² body surface due to highly active multiple sclerosis. On treatment with rituximab she did not show any hematologic abnormalities. After interruption of treatment due to pregnancy she was switched to ocrelizumab and developed grade IV LON with neutrophil counts as low as 0.1x109/L.
This first case of LON in a patient treated with different anti-CD20 antibodies highlights the necessity of regular hemogram examinations on treatment with ocrelizumab. Patients may develop LON during ocrelizumab even if rituximab was previously well tolerated.