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NMO spectrum disorder and optic neuritis: are VEPs useful?

Objectives: the aim of our study was to investigate whether the presence of IgG-NMO antibody is associated with a different pattern of response at visual evoked potentials (VEPs) in patients affected by neuromyelites optica spectrum of disorders (NMOsd) with optic neuritis (ON). Methods: we retrospectively studied clinical, immunological and neurophysiological data from 28 patients affected by NMOsd who presented at least one optic neuritis (16 patients bilateral and 12 unilateral). All the patients underwent IgG-NMO antibody testing and pattern-reversal checkerboard VEPs at check-size 15’. Bilateral ON was present in 6/11 (55%) Ig-NMO positive patients and 10/17 (59%) IgG-NMO negative patients. Latency and presence of VEPs response over the affected and unaffected eyes were determined. Results: All non affected eyes had a measurable VEP response. No significant effect of the presence of IgGNMO was found concerning VEPs latencies in non affected eye. Concerning eyes previously affected by NO, the presence of IgG-NMO was significantly associated with a higher frequency of absence of VEPs (70% vs 36%; p= 0.02 Fischer). In eyes with presence of cortical VEP responses (5 from IgG-NMO positive and 17 from IgG-NMO negative patients), no significant latency differences were found according to the presence of IgG-NMO. Conclusions: Our main result was a more frequent absence of visual evoked responses after optic neuritis in the presence of NMO antibodies in patients with NMOsd. This finding suggests a pathological process characterized by a more frequent and severe axonal involvement associated with the presence of NMO antibodies. If validated by future studies, these results may suggest a possible usefulness of VEPs in the differential diagnosis of NMO.

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