Most but not all cases of Neuromyelitis Optica Spectrum Disorder (NMOSD) are associated with Aquaporin-4 (AQP4) or myelin oligodendrocyte glycoprotein (MOG) antibodies.
To determine the core clinical characteristics of seronegative NMOSD patients fulfilling 2015 International Diagnostic consensus criteria, treated in the National NMOSD service.
Retrospective review of patient databases at The Walton Centre for Neurology and Neurosurgery and The John Radcliffe Hospital (Neuromyelitis Optica National Referral Centres) between 1st January 2010 - 17th January 2020.
Of NMOSD=727, 49(7%) were seronegative. The male to female ratio was 1:2.5 and median age at onset was 36(5-57) years. In 2/3 of patients the index presentation was myelitis=22 or myelitis+optic neuritis=11. In 26/33 (79%), longitudinally extensive myelitis was present. Optic neuritis=9 (4 bilateral) and brain involvement=7 were also seen. Relapsing disease was observed in 39/49(80%) of patients. The median annualised attack rate was 0.58 over a median disease duration of 78 (3-258) months. Unmatched CSF oligoclonal bands (CSF-OCBs) were detected in 4/38(11%) and 31/49(63%) fulfilled multiple sclerosis (MS) diagnostic criteria. Immunosuppression (typically Mycophenolate and Rituximab) was used in 34/49(69%). Median last EDSS was 4 (1-10) with death recorded in 5/49 (10%) patients.
Seronegative NMOSD is uncommon. Longitudinal myelitis with/without optic neuritis is a common initial presentation. Similar to AQP4-IgG, NMOSD disability and mortality rates are high. Absence of unmatched CSF-OCB and typical brain lesions help to distinguish this disease from MS.