Neuromyelitis Optica Spectrum Disorders Tetsuya Akaishi, MD a , Ichiro Nakashima, MD a , Douglas Kazutoshi Sato, MD a,b,c , Toshiyuki Takahashi, MD a,d , Kazuo Fujihara, MD a,b,e, * INTRODUCTION Neuromyelitis optica (NMO) is clinically character- ized by severe optic neuritis (ON) and transverse myelitis. NMO spectrum disorder (NMOSD) is a newly emerging disease spectrum with or without anti-aquaporin-4-autoantibody (anti-AQP4-Ab) and includes typical NMO. Until recently, ON (often severe and simultaneous bilateral) and acute trans- verse myelitis (mostly longitudinally extensive, >3 vertebral segments) have been the cardinal clinical symptoms of NMO and were absolutely needed for the diagnosis. Then the term NMOSD was intro- duced for anti-AQP4-Ab-seropositive cases with Disclosure Statements: See last page of article. a Department of Neurology, Tohoku University Graduate School of Medicine, 1-1 Seiryomachi, Aobaku, Sendai 980-8574, Japan; b Department of Multiple Sclerosis Therapeutics, Tohoku University Graduate School of Med- icine, 1-1 Seiryomachi, Aobaku, Sendai 980-8574, Japan; c Brain Institute, The Pontifical Catholic University of Rio Grande do Sul, Av. Ipiranga, 6690 - Building 63, Porto Alegre, Rio Grande do Sul 90610-000, Brazil; d Department of Neurology, Yonezawa National Hospital, 26100-1 Misawa, Yonezawa 992-1202, Japan; e Department of Multiple Sclerosis Therapeutics, Multiple Sclerosis & Neuromyelitis Optica Center, Southern TOHOKU Research Institute for Neuroscience, Fukushima Medical University School of Medicine, 7-115 Yat- suyamada, Koriyama 963-8563, Japan * Corresponding author: Department of Neurology, Tohoku University Graduate School of Medicine, 1-1 Seir- yomachi, Aobaku, Sendai 980-8574, Japan. E-mail address: fujikazu@med.tohoku.ac.jp KEYWORDS  Neuromyelitis optica spectrum disorders  Anti-aquaporin-4 antibody  Anti-myelin oligodendrocyte glycoprotein antibody  MR imaging  Optical coherence tomography KEY POINTS  Neuromyelitis optica spectrum disorders (NMOSD) is now divided into anti-aquaporin-4-antibody (anti-AQP4-Ab)-seropositive NMOSD and -seronegative NMOSD (or unknown serostatus).  In anti-AQP4-Ab-seropositive NMOSD, optic neuritis (ON) is often severe and may involve the optic chiasm, and acute myelitis is longitudinally extensive (>3 vertebral segments) and preferentially in- volves the central gray matter. Area postrema lesions associated with intractable hiccup, nausea, and vomiting, and other brain syndromes may develop in some patients.  A fraction of anti-AQP4-Ab-seronegative patients with NMOSD are positive for anti-myelin oligo- dendrocyte glycoprotein-antibody (anti-MOG-Ab), and anti-MOG-Ab-seropositive NMOSD has some unique features as compared with anti-AQP4-Ab-seropositive NMOSD (fewer relapses and better prognosis, simultaneous bilateral ON, lumbosacral myelitis). Double-seronegative NMOSD might include heterogeneous groups of diseases.  Optical coherence tomography shows relatively milder neuronal damage in anti-MOG-Ab- seropositive ON than in anti-AQP4-Ab-seropositive ON.  MR imaging and OCT are powerful tools to diagnose and evaluate both types of autoantibody- associated NMOSD. Neuroimag Clin N Am - (2017) -–- http://dx.doi.org/10.1016/j.nic.2016.12.010 1052-5149/17/Ó 2017 Elsevier Inc. All rights reserved. neuroimaging.theclinics.com