OBJECTIVES: To study the clinical and economic burden associated with misdiagnosis of neuromyelitis optica spectrum disorders (NMOSD) as multiple sclerosis (MS).

METHODS: We analyzed claims from the IBM MarketScan Commercial and Medicare Supplemental Databases. Patients with NMO were identified in 2016-2019 who had ≥1 claim with an ICD-10-CM diagnosis for NMO (or ≥1 claim for transverse myelitis and optic neuritis) and ≥1 claim with an NMO drug or had ≥2 NMO diagnosis claims ≥90 days apart. Newly diagnosed patients required ≥1 diagnosis in 2016-2018 (first defined as the index date) and lacked an NMO diagnosis during 1 year pre-index (baseline). Exclusion criteria: disenrollment during baseline or 1 year post-index (follow-up); MS diagnosis/drug or sarcoidosis diagnosis after the last NMO diagnosis/drug; evidence of secondary NMO. Clinical characteristics, utilization, and costs compared for two groups: NMO patients with baseline misdiagnosis of MS (≥2 MS diagnosis claims or ≥1 MS drug claim) vs those without.

RESULTS: Of 163 NMO patients identified, 24(14.7%) were misdiagnosed with MS. Misdiagnosed patients (vs not) had mean(SD) age of 42.9(13.1) vs 49.5(13.6) years (P=0.028), were 79.2% vs 76.3% (P=0.756) female, and had Charlson Comorbidity Index of 0.9(1.1) vs 1.3(2.1) (P=0.221). High utilization and costs, often higher in those misdiagnosed, were observed in both groups: baseline—hospitalization (41.7% vs 30.9%; P=0.300), MRI use (79.2% vs 49.6%; P=0.007), number of office visits (22.3[18.6] vs 12.7[13.1]; P=0.005), high-dose IV steroid use (33.3% vs 15.1%; P=0.031), total costs ($64,831[72,294] vs $37,827[65,536]; P=0.068); follow-up—hospitalization (33.3% vs 46.0%; P=0.247), MRI use (70.8% vs 66.9%; P=0.705), office visits (23.8[21.9] vs 19.6[18.6]; P=0.274), high-dose IV steroid use (50.0% vs 37.4%; P=0.243), total costs ($74,275[53,919] vs $98,514[137,708]; P=0.135). In misdiagnosed patients, 41.7% received MS medication before receiving a correct NMO diagnosis.

CONCLUSIONS: Patients with NMOSD experience substantial burden, which may be worsened by prior MS misdiagnosis.