Postwithdrawal Rebound Increase in T2 Lesional Activity in Natalizumab-Treated MS Patients

Natalizumab significantly reduces relapse rate, disability progression, and lesion development in relapsing multiple sclerosis (MS).1,2 Dosing was suspended when cases of progressive multifocal leukoencephalopathy were reported and reintroduced after a safety analysis of all patients being treated with natalizumab had been completed.3 Our center participated with 23 patients in the phase III program (13 in AFFIRM Natalizumab Safety and Efficacy in Relapsing Remitting Multiple Sclerosis, 10 in SENTINEL Safety and Efficacy of Natalizumab in Combination with Interferon β-1a in Patients with Relapsing Remitting Multiple Sclerosis). All patients underwent safety MRI shortly after dose suspension and unenhanced MRI as part of the baseline assessments before reintroduction of natalizumab. The neuroradiologist who reviewed these images noticed that in some patients a considerable number of new lesions had developed in this 15-month interval. As for these patients longitudinal MRI data were available from the period before natalizumab treatment, we performed a formal analysis comparing the annualized number of new MRI lesions in the period before patients started with natalizumab vs the 15-month interval after withdrawal of natalizumab. ### Methods. Patients randomized to natalizumab had active treatment during the double-blind and extension phases of the study (30 to 37 infusions, median 36). Patients randomized to …