Highlights
- Unlike Multiple Sclerosis, the risk of relapse in AQP4-IgG positive Neuromyelitis Optica Spectrum Disorder (NMOSD) does not decrease with advancing age.
- Older age at disease onset (>55 years) is a potent independent predictor of more rapid disability accumulation (reaching EDSS milestones 4 and 6).
- High-efficacy therapies (HET) significantly reduce annualized relapse rates (ARR) across all age groups compared to low-efficacy therapies (LET).
- Higher baseline disability and treatment delays are critical modifiable factors for long-term morbidity.
Background
Neuromyelitis Optica Spectrum Disorder (NMOSD) associated with antibodies against aquaporin-4 (AQP4-IgG) is a severe, inflammatory astrocytopathy characterized by recurrent attacks of optic neuritis, transverse myelitis, and area postrema syndrome. For decades, clinical management of NMOSD was often extrapolated from Multiple Sclerosis (MS) protocols. However, MS is characterized by a distinct age-dependent phenotype where inflammatory relapse activity typically diminishes as patients age, often transitioning into a progressive phase with fewer acute episodes. This phenomenon in MS sometimes allows for the consideration of treatment de-escalation in older cohorts.
The relationship between age and disease activity in NMOSD has remained controversial. While some smaller studies suggested that older onset might influence the severity of the first attack, global data on how age at onset dictates long-term relapse risk and disability accrual has been inconsistent. Understanding these dynamics is essential for clinicians to determine if age should influence the intensity and duration of preventive immunotherapy.
Key Content
Study Design and Patient Demographics
A comprehensive retrospective multicenter cohort study utilizing the international MSBase registry analyzed 539 AQP4-IgG positive patients. The cohort was stratified into three distinct age-at-onset groups: Pediatric (<18 years; n=42), Early-onset (18–55 years; n=421), and Late-onset (>55 years; n=76). The median age at onset was 35 years, with a heavy female predominance (85.2%), consistent with the known epidemiology of AQP4-IgG NMOSD. The median disease duration of 7.42 years provided a robust window for observing long-term outcomes.
Stability of Relapse Risk Across the Lifespan
The most striking finding of this evidence synthesis is the lack of correlation between age at onset and relapse risk. Unlike the immunosenescence-related decline in inflammatory activity seen in MS, patients with NMOSD remained at high risk for relapses regardless of whether their disease began in childhood or late adulthood. Both the Annualized Relapse Rate (ARR) and the time to first relapse showed no statistically significant differences between the pediatric, early-onset, and late-onset groups. This suggests that the pathogenic mechanism of AQP4-IgG—primarily a complement-mediated astrocytopathy—is not subject to the same age-related tempering as the T-cell mediated processes in MS.
Accelerated Disability Accrual in Late-Onset Patients
While relapse rates were stable, the consequences of those relapses—and the baseline progression of the disease—differed significantly by age. Late-onset patients (>55 years) reached significant disability milestones (EDSS 4, indicating limited walking ability, and EDSS 6, requiring a walking aid) much faster than their younger counterparts. Cox proportional models indicated that advancing age at onset was an independent predictor of faster disability accumulation. This disparity likely stems from a combination of reduced central nervous system (CNS) repair capacity in older patients, the presence of age-related comorbidities, and a potentially more destructive inflammatory response during acute attacks in an aging microenvironment.
Efficacy of Immunotherapy: HET vs. LET
The study differentiated between high-efficacy therapies (HET)—typically including monoclonal antibodies like rituximab, eculizumab, satralizumab, and inebilizumab—and low-efficacy therapies (LET) or traditional immunosuppressants like azathioprine and mycophenolate mofetil.
- Relapse Prevention: HET was significantly superior to LET in reducing the risk of relapse (p < 0.001) across all age strata.
- Disability Mitigation: Delayed initiation of treatment was identified as a major risk factor for reaching EDSS 4 and 6. Patients who received prompt, highly effective intervention early in their disease course had significantly better locomotor outcomes.
The ‘Window of Opportunity’ and Baseline Disability
Another critical finding was that higher baseline EDSS scores were predictive of future disability progression. This reinforces the “window of opportunity” hypothesis in NMOSD: because disability in this disease is almost entirely relapse-driven (unlike the secondary progression of MS), preventing even the very first few relapses is paramount. In older patients, where the first attack is often more severe, this window is even narrower.
Expert Commentary
The findings by Siriratnam et al. (2026) represent a paradigm shift in how we approach the aging NMOSD patient. For years, there has been a clinical temptation to “ease off” on aggressive immunosuppression as patients age, fearing the side effects of monoclonal antibodies in the elderly. However, these data suggest that such a strategy is fundamentally flawed in NMOSD. Since the relapse risk does not wane with age, but the functional impact of each relapse increases, the elderly patient actually has the most to lose from under-treatment.
The biological rationale for this is likely linked to the fact that AQP4-IgG NMOSD is a primary astrocytopathy. Astrocytes provide critical metabolic and structural support to neurons. In an aging brain, where astrocyte function is already naturally declining, the antibody-mediated destruction of these cells leads to more immediate and irreversible neuronal loss compared to younger brains with higher plasticity. Furthermore, the reliance on EDSS, while standard, may actually underestimate the burden of disease in older adults, who may have concurrent orthopedic or vascular issues that synergize with neuroinflammatory damage.
One controversy remains: the definition of HET. While rituximab has been the historical gold standard for HET, the newer FDA-approved agents (eculizumab, inebilizumab, and satralizumab) have shown even more profound suppression of attacks in clinical trials. Future research should focus on whether these newer biologics can specifically narrow the disability gap for late-onset patients.
Conclusion
In conclusion, age at onset is a critical determinant of disability but not of relapse risk in AQP4-IgG NMOSD. The persistent risk of inflammatory activity across the lifespan distinguishes NMOSD from MS and mandates a lifelong commitment to effective immunotherapy. For clinicians, the message is clear: do not de-escalate treatment based on age alone. Instead, prioritize early, high-efficacy therapy to preserve function, especially in late-onset cases where the trajectory toward disability is most aggressive. Future research must explore the molecular basis for why the AQP4-IgG inflammatory response evades the typical effects of immunosenescence.
References
- Siriratnam P, Jokubaitis VG, Van Der Walt A, et al. Impact of Age at Onset on Relapse and Disability in AQP4-IgG Neuromyelitis Optica Spectrum Disorder. Neurology. 2026-03-05;106(7):e214707. PMID: 41785437.
- Wingerchuk DM, Banwell B, Bennett JL, et al. International consensus diagnostic criteria for neuromyelitis optica spectrum disorder. Neurology. 2015;85(2):177-189. PMID: 26084683.
- Pittock SJ, Berthele A, Fujihara K, et al. Eculizumab in Aquaporin-4-Positive Neuromyelitis Optica Spectrum Disorder. N Engl J Med. 2019;381(7):614-625. PMID: 31050277.
