Is It Too Early to Predict the Failure of Natalizumab in NMO?—Reply

In reply

We appreciate Drs Govindarajan and Salgado describing a NMO IgG antibody–positive patient who had a 6-year course of clinical stability under natalizumab before becoming progressive. While such a long period with a good treatment response to natalizumab is noteworthy, several aspects of this patient are untypical for neuromyelitis optica (NMO). Only 13.7% of patients are older than 60 years at disease onset,¹ 8% have an elevated IgG index, and 16.4% show oligoclonal bands.² Disease progression without relapses is uncommon in NMO,³ and it remains unclear whether optic neuritis was present, completing the full picture of NMO. In a patient with untypical clinical presentation, the verification of aquaporin 4 antibodies is of particular importance to make the diagnosis of NMO. Diagnostic tests applied to measure aquaporin 4 antibodies vary considerably regarding sensitivity and specificity, and immunohistochemical methods to detect NMO IgG additionally depend on the experience of the examiner.⁴