Momen and colleagues ^{Reference Momen, Freedman and Fadda1} present a multicentre retrospective cohort study of the baseline characteristics of adults with aquaporin-4 IgG positive (AQP4+) neuromyelitis optica spectrum disorder (NMOSD) enrolled in the prospectively followed CAnadian Neuromyelitis OPTIca Spectrum Disorder and other atypical demyelinating diseases Cohort Study (CANOPTICS).

This manuscript helps further define the contours of the demographic, diagnostic and treatment landscapes of this rare neuroinflammatory disease within a universal, but provincially variable, healthcare system, and adds a Canadian perspective to the established literature.

The epidemiological findings corroborate those already established. ^{Reference Hor, Asgari and Nakashima2} The overwhelming majority (84.9%) of patients were female, and there was an overrepresentation of Black and Asian individuals, compared to the General Canadian population. While possibly just a factor of age at immigration, 91.3% of those immigrants with a known arrival date had their first attack after arrival – pointing towards a possible environmental trigger. Future analyses could look at the age of immigration and country of origin and determine whether the epidemiology differs between the immigrant community and the source country.

While study inclusion hinged on AQP4 positivity, the serological testing was heterogeneous – with 42.3% being enzyme-linked immunosorbent assays, which is generally considered less sensitive and specific than a cell-based assay. ^{Reference Jarius, Aktas and Ayzenberg3} This, in addition to differences in MRI sequences obtained, highlights some of the inequities in access to diagnostic tools.

As with prior studies, ^{Reference Pekmezovic, Jovicevic and Andabaka4} a substantial percentage (24.8%) had a comorbid autoimmune disease. Treatments for these conditions were not reported, precluding determination of how they may have affected treatment choice for NMOSD.

A lower median EDSS (3.0) than historical cohorts (up to 6.5 ^{Reference Pandit, Asgari and Apiwattanakul5} ) suggests that early treatment may help stave off future disability. Unfortunately, use of proven high-efficacy therapy (such as rituximab ^{Reference Tahara, Oeda and Okada6} or the novel monoclonal antibodies) remains lagging, and azathioprine was the most common first-line treatment choice – although the use of high-efficacy therapies has been increasing over time. This may represent inequities in treatment access and could act as a focus point for future advocacy.

While the usual biases of observational data may be present – such as selection bias or ascertainment bias excluding patients followed outside of speciality clinics – this study provides a strong base for our understanding of NMOSD in Canada. It will be of great interest to see what the prospective data will illuminate in regard to prognosis, prognostic factors, diagnostic approaches, changes in treatment patterns, comparative treatment efficacy and other – practical – real-world outcomes.