Is Devic's neuromyelitis optica a separate disease? A comparative study with multiple sclerosis

Devic's neuromyelitis optica (NMO) associates optic neuritis and myelopathy without other neurological signs. Many patients with NMO may be diagnosed as having multiple sclerosis (MS). However, there have been no previous studies comparing these two pathologies and it is still unclear if NMO is a separate entity or a subtype of MS. In the present study, we compared a series of NMO patients with a series of MS patients for whom optic neuritis or myelopathy was the presenting symptom, in order to determine the place of NMO in the spectrum of MS. We retrospectively studied 30 patients diagnosed with NMO and we compared these patients with 50 consecutive MS cases revealed by optic neuritis or acute myelopathy. MS patients were only included if a relapse occurred demonstrating time and space dissemination. We compared the two groups in terms of clinical presentation, laboratory findings (MRI and CSF) and clinical outcome. NMO patients were older and more frequently women than MS patients but the difference was not significant. CSF and MRI data were clearly different: oligoclonal bands (OCB) were found in 23% of NMO cases and 88% of MS (P < 0.001), abnormal brain MRI data were observed in 10% of NMO cases and 66% of MS (P < 0.001) and a large spinal cord lesion was observed in 67% of NMO cases and 7.4% of MS cases (P < 0.001). Clinical outcome was evaluated as more severe in the NMO group (P < 0.001). On the basis of clinical data, all NMO patients but three had dissemination in time and space. When we included MRI parameters, only two of the NMO patients met criteria for MS and one of the MS patients met criteria for NMO. Our study demonstrates that NMO and MS should be considered as two different entities. The respective criteria for NMO and MS were able to distinguish these two pathologies but only when MRI data were applied. This finding could have implications for future therapeutic trials.