To revisit MS diagnosis in an era of antibody testing availability for NMOSD.

It is unclear if the McDonald criteria for MS can sufficiently establish the diagnosis of MS when history, symptoms, and radiological findings overlap with NMOSD. This is particularly relevant given the commercial availability of highly specific, serum-based antibody testing for NMOSD. Current guidelines for either disease may not adequately separate these two inflammatory disorders.

Retrospective data analyses from 2009-2016 were done based on preliminary data extracted from Truven Health Analytics (THA) database derived from ICD 9/10 codes for patients who had a diagnosis of MS followed by a later diagnosis of NMOSD. A retrospective, individual patient-based data search was then done at our medical center based on either AQP4 or MOG Ab positive status. Only cases that had unequivocal clinical/radiological findings suggestive of MS were included.

MS was diagnosed in 319,994 individuals in the THA claims database between 2009-2016. Of these, 2,001 had diagnosis of NMOSD. A retrospective data search revealed 54 cases had serum testing for AQP4 or MOG Ab. 4 of 54 were positive. All four cases had clinical and radiological features of MS based on McDonald criteria, but serum antibody testing revealed NMOSD.

Our findings question whether guidelines help delineate the two diseases based on current recommendations. The results from our small study could have significant implications; symptoms, clinical presentation, and classic radiological findings alone might not suffice to diagnose MS. Since no single test can conclusively establish a diagnosis of MS, perhaps NMOSD may have to be excluded first despite typical radiological findings pointing to MS. The question of repeat NMOSD testing in ‘poorly responsive’ MS patients to standard disease-modifying therapies (DMD) ought to be investigated further since NMOSD patients who are deemed to have MS will likely fail disease-modifying drugs.