Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune disease that often results in transverse myelitis and optic neuritis. Like most autoimmune diseases, its prevalence varies throughout the world. 

One of the latest epidemiological studies on the global prevalence and incidence of NMOSD was written by Papp and colleagues, who sought to map out the “worldwide prevalence, incidence, and basic demographic characteristics of NMOSD.” Their findings were published in Neurology. 

The research team collected data on the prevalence of the disease in different countries and regions, as well as among different races. They found the following approximate incidence rates:


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  • 0.7/100,000 person-years among the Caribbean-African population
  • 0.39-0.6/100,000 person-years in some Asian populations
  • 0.17/100,000 person-years in Arabic populations
  • 0.07-0.4/100,000 person-years in smaller, predominantly Caucasian cohorts
  • 0.029-0.04/100,000 person-years in larger Caucasian cohorts.

“NMOSD has been described worldwide, but it seems to be less frequent in White populations compared with Asian and African ones,” the authors noted.

The validity of the data collected from different parts of the world is limited by the different definitions of NMOSD under different healthcare jurisdictions. Nevertheless, it is clear that NMOSD is an extremely rare disease in any part of the world.

The Influence of Genetics

In Frontiers in Neurology, Hor and colleagues conducted a similar study on the prevalence and incidence of NMOSD worldwide. Their research included a comparison of epidemiological data for East Asians, Blacks, and Whites/Caucasians. 

Hor et al reported a prevalence of NMOSD of around 3.5/100,000 in the East Asian population, which is higher than in Whites or other Asian racial groups. This figure is consistent with genetic studies suggesting that Japanese and Chinese people share the same human leukocyte antigen (HLA) risk genes for NMOSD, which are HLA-DPB1*05:01 and HLA-DRB1*16:02. 

Read more about NMOSD epidemiology

The prevalence of NMOSD has also been consistently higher in the Black community than in the White community. This is evident even among Black and White populations living in the same country; for example, the prevalence of NMOSD is higher among Blacks than Whites in locations as diverse as Cuba, Martinique Island, Australia, New Zealand, and Liverpool in the UK. Nevertheless, the research team cautioned, “As Blacks are genetically diverse, more data from different geographical regions are needed, and especially those from the African continent.” 

The prevalence of NMOSD among Whites has been consistently around 1/100,000. This figure is derived from studies on White populations in Australia, New Zealand, Catalonia in Spain, Denmark, and Sweden. The researchers did find an outlier—Hungary. The prevalence of NMOSD among Hungarians was higher than average, at 1.91/100,000, which the authors of the study attributed to admixtures of Asian genes (from Northeast Asia) among Hungarians. 

Researchers studying the epidemiology of NMOSD have also identified trends related to sex and age.

“All studies that calculated the sex-specific estimates found the highest prevalence among females, which was 2.3-7.6-times greater than for males, both in Whites and Africans,” Papp et al wrote. The sex-specific incidence rates of NMOSD were less remarkable at the extremes of age. 

The age of peak NMOSD prevalence among females in 4 locations (Australia, New Zealand, Tehran, and Cuba) was between 40 and 49 years. The highest NMOSD incidence rate among men was between the ages of 40 and 59. 

With regards to the age of NMOSD onset, younger patients were more likely to experience optic neuritis as an onset attack, while older patients usually developed myelitis as the first symptom of the disease. In addition, studies have shown that younger-onset patients who developed optic neuritis were more likely to experience recurrence and had a higher risk of developing blindness compared to older patients. However, younger patients were more likely to recover from myelitis without permanent motor disability, compared to older patients. 

Data Quality Considerations

Any attempt at collecting global epidemiological data raises the question of the quality of data being studied. It is no secret that official figures are sometimes distorted for various purposes, but even assuming this is not the case, it is a fact that the definition of NMOSD has evolved over the years. For example, NMOSD was once thought to be the same disease entity as multiple sclerosis. It was only later that a clear distinction was made between the 2 diseases. 

Read more about NMOSD patient education 

In addition, some locations lack the capacity for aquaporin-4 (AQP4) antibody testing. Public health education is another important issue; some populations are less aware of this disease than others (given its rarity) and are hence less likely to seek appropriate medical help when warranted. 

However, we have reasons to be optimistic. According to Papp and colleagues, “the number of well-designed epidemiological studies of NMOSD is increasing.”

This is a trend that can be observed across medical disciplines; disease names, diagnostic thresholds, and clinical outcomes have all become more uniform over the years. As our collective capacity for epidemiological reporting increases, we can expect higher-quality data on NMOSD to emerge in the coming years. 

References

Hor JY, Asgari N, Nakashima I, et al. Epidemiology of neuromyelitis optica spectrum disorder and its prevalence and incidence worldwideFront Neurol. 2020;11:501. doi:10.3389/fneur.2020.00501

Papp V, Magyari M, Aktas O, et al. Worldwide incidence and prevalence of neuromyelitis optica: a systematic reviewNeurology. 2021;96(2):59-77. doi:10.1212/WNL.0000000000011153