Brain lesions are not uncommon in neuromyelitis optica (NMO) patients with anti-aquaporin-4 (AQP4) antibody; however, the appearance of these lesions is said to be different from that of those in Western patients with multiple sclerosis (MS). To clarify the similarities and dissimilarities of brain lesions in anti-AQP4 antibody-positive and -negative MS and NMO patients, we examined the presence of anti-AQP4 antibody in the sera of 148 consecutive patients fulfilling Poser's criteria for clinically definite MS, of whom 38 also met the revised NMO criteria, using an immunofluorescence method, and analyzed brain lesions by magnetic resonance imaging (MRI). Brain lesions fulfilling the Barkhof criteria were significantly more common in 121 patients without anti-AQP4 antibody than in 27 patients with anti-AQP4 antibody (57.0% vs. 33.3%, P = 0.033), while the frequency of those that met the Paty criteria was not different between the two groups (74.4% vs. 73.5%). Ovoid lesions were detected more commonly in patients without anti-AQP4 antibody than in those with the antibody (72.3% vs. 48.2%, P = 0.022). The anti-AQP4 antibody-positive patients had significantly more atypical brain lesions, such as extensive brain lesions, than the anti-AQP4 antibody-negative ones (18.5% vs. 1.7%, P = 0.0023). Thus, although MS-like brain lesions are more common in anti-AQP4 antibody-negative patients than anti-AQP4 antibody-positive patients, approximately 30 to 50% of patients with anti-AQP4 antibody harbour brain MRI lesions indistinguishable from those present in typical MS patients, such as periventricular ovoid lesions, suggesting the existence of considerable overlap in brain MRI features between anti-AQP4 antibody-positive and -negative Asian patients. In the present study, NMO patients with brain lesions showed a significantly higher annualized relapse rate (Pcorr = 0.017) and higher frequency of anti-AQP4 antibody (Pcorr < 0.0001) than typical NMO patients without brain lesions, suggesting that development of brain lesions in NMO may reflect high disease activity and thus be a warning sign.
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