[Clinical features of NMO according to brain MRI findings]

Neuromyelitis optica (NMO) is a severe inflammatory, demyelinating disease, and its clinical characteristics include recurrent optic neuritis and longitudinally extensive transverse myelitis. The NMO-immunoglobulin (Ig) G auto-antibody (Ab), which binds to the aquaporin-4 (AQP4) water channel protein, is a marker for NMO. These clinical and immunological features have been used to distinguish NMO from multiple sclerosis (MS). In 1999, Wingerchuk et al. broadened the clinical criteria for diagnosing NMO to include "negative brain magnetic resonance imaging (MRI) at onset." However, after NMO-IgG/AQP4-Ab became a supportive criterion for diagnosing NMO, patients with NMO were frequently found to have symptomatic or asymptomatic brain lesions. In 2006, Pittock et al. reported that asymptomatic brain lesions were common in NMO, and that NMO brain lesions characteristically occurred in the hypothalamus and periventricular areas, which correspond to brain regions with high levels of AQP4 expression. Furthermore, Nakashima et al. detected abnormalities on brain MRI in 71% of NMO-IgG-positive Japanese patients. Patients with NMO have unique brain lesions that are clearly different from the lesions of patients with MS. In patients with NMO, involvement of the dorsal portion of the medulla oblongata causes intractable hiccups and nausea. Some studies described a hypothalamic lesion, and hypothalamic dysfunction could cause symptomatic hypersomnia, narcolepsy, and endocrinopathies. In some patients with NMO and NMO spectrum disorder who experience blood pressure fluctuations, vasogenic edema, manifesting as posterior reversible encephalopathy syndrome, may occur. In a recent report highlighting brain MRI with contrast enhancement, the most prominent feature that appeared to be a specific finding in NMO was "cloud-like enhancement" with multiple patchy enhancing lesions with a blurred margin. Another report showed that acute, large, edematous callosal lesions with heterogeneous intensity ("marbled pattern") occasionally occur in NMO. This review presents the characteristic clinical features of NMO according to the brain MRI findings and the features that can be used to distinguish NMO from MS.