Diagnostic delay and poor functional outcomes in late-onset NMOSD: A Thai cohort study

Late-onset neuromyelitis optica spectrum disorder (LONMOSD) may be difficult to recognize because symptoms can mimic other neurological disorders in older patients. Data on LONMOSD in Thailand remain limited.

To compare clinical characteristics and outcomes between early-onset NMOSD (EONMOSD) and LONMOSD in a Thai cohort, and to evaluate the impact and causes of delayed diagnosis in LONMOSD.

We retrospectively studied adult patients with NMOSD who fulfilled the 2015 International Panel for NMO Diagnosis criteria at a tertiary referral center in Thailand from 2016 to 2025. LONMOSD was defined as onset at age ≥50 years. Clinical characteristics, treatment, Expanded Disability Status Scale (EDSS), relapse outcomes, and reasons for delayed diagnosis were analyzed.

Among 148 patients, 91 had EONMOSD and 57 had LONMOSD. LONMOSD was associated with more frequent delayed diagnosis than EONMOSD (54.4%vs 31.9%, P = 0.01). LONMOSD patients had higher EDSS at nadir, 90 days, and 180 days, and lower recovery index at 180 days. Relapse outcomes and time to subsequent relapse were not significantly different between groups. In LONMOSD, myelitis was independently associated with EDSS ≥6 at 90 and 180 days, while delayed diagnosis was associated with EDSS ≥6 at 90 days. Misdiagnosis was the main cause of delayed diagnosis, most commonly cerebrovascular disease and compressive myelopathy.

LONMOSD was associated with delayed diagnosis and worse functional outcomes. Early recognition may reduce preventable disability in older patients.