Introduction Ocrelizumab is a recombinant humanised monoclonal antibody that selectively depletes CD20 expressing B lymphocytes. Ocrelizumab was approved in Australia for use in relapsing-remitting and primary-progressive multiple sclerosis in July 2017. Rare incidences of late onset neutropenia with ocrelizumab have been reported (3 cases worldwide, none in Australia).
Case A 40-year-old man of Lebanese descent with multiple sclerosis, diagnosed 11 years ago and stabilized with 600 mg 6-monthly ocrelizumab since March 2018, presented in November 2019 with lethargy and myalgia, two weeks after his fourth cycle of ocrelizumab. Clinical examination was unremarkable. Full blood count showed white cell count of 2.35x109/L and absolute neutrophil count of 0.1x109/L with normal lymphocyte count, peripheral blood film, haemoglobin and platelet count. Serum iron studies, B12, folate, C-reactive protein, thyroid function were normal and so was the chest x-ray. The urine microscopy showed sterile pyuria. Electrolytes, liver function and renal function were normal. The nasopharyngeal viral swabs were negative. MRI brain-cervical spine showed stable old plaques and no enhancement with contrast. He had no other co-morbid condition and was not taking any other prescribed or over-the-counter medications. The neutrophil count improved to 7.68x109/L in 48 hours after Filgrastim 400 mcg subcutaneously. Ocrelizumab was ceased.
Conclusion Late onset severe neutropenia is rarely reported with ocrelizumab. In our case, the neutropenia occurred after 1.5 years of ocrelizumab use and the mechanism remains unclear. The case raises the issue of ocrelizumab re-exposure vs cessation in these patients and highlights the importance of monitoring of serial blood count.
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