MG cases up in 3 Nordic countries, 20-year population study shows
Denmark, Finland, Sweden saw total, new cases rise from 2000-2020
Myasthenia gravis (MG) cases increased gradually from 2000 to 2020 in Denmark, Finland, and Sweden, with the total number of cases and the number of newly diagnosed cases both rising, according to a population-based study.
The number of newly diagnosed cases was higher among men older than 50 and women younger than 50 during the period. The mortality rate remained stable, even though it was higher than that seen in the general population.
“The findings of this study highlight the importance of careful management of patients with MG and the need for further improved care, especially in the younger age groups of women,” the researchers wrote.
The study, “Epidemiology of myasthenia gravis in Denmark, Finland and Sweden: a population-based observational study,” was published in the Journal of Neurology, Neurosurgery & Psychiatry.
MG is a disease marked by muscle weakness and fatigue that’s generally caused by self-reactive antibodies targeting and attacking proteins involved in nerve-muscle communication, most commonly acetylcholine receptors.
Incidence, prevalence, mortality
Studies have shown the incidence, or number of newly diagnosed cases, of MG varies with age, sex, and ethnicity, the researchers wrote, noting that “there are limited nationwide population-based epidemiological data available” and the “mortality risk is rarely addressed.”
They used nationwide health registries to analyze MG incidence, prevalence (total number of cases), and mortality in Denmark, Finland, and Sweden.
Of a total of 11,136 patients identified from 2000 and 2020, 6,415 patients (1,559 in Denmark, 1,797 in Finland, and 3,059 in Sweden) were included in the analysis.
Slightly more than half of the patients were men (51%-52%). They had a median age of 64.9 to 67.5, and were followed for a median of 5.9 to 7.3 years. Men were older than women at the time of diagnosis (median age of 67.4 vs. 62.6).
The overall MG incidence during the study period ranged from 1.34 to 1.68 per 100,000 people and increased over time in all three countries. The overall incidence was higher in men than in women. In men, there was a steeper increase in MG incidence from age 50 on, while in women the incidence of MG was higher among those younger than 50.
The overall prevalence of MG during the study period varied from 18.6 to 23.4 cases per 100,000 people, and also increased over time. MG prevalence was higher in women than in men, and increased gradually over time in both men and women.
“In general, the increasing incidence and prevalence could be the result of, for example, the rise in the incidence of autoimmune diseases, ageing of the population, increased life expectancy, improved diagnostics and access to testing, [and] improvement of the quality of register data over time,” the researchers wrote.
Survival rates
MG patients had an overall survival rate of 84% at five years of follow-up, 70% at 10 years, and 58% at 15 years. The standardized mortality ratio (SMR), the ratio between the number of deaths seen in the study and the number of deaths that would be expected to occur in the general population, was 20% to 32% higher among MG patients.
The overall SMR was also higher among women than in men, which according to researchers, “could reflect the earlier age at diagnosis in women or possibly suboptimal management of MG in women.”
The most common causes of death across the three countries were MG-related (15.4%), chronic ischemic heart disease, or shortage of blood and oxygen supply to the heart muscle due to narrowing of the coronary arteries (6.8%), and heart attack (6.4%).
Further analyses indicated the risk of death significantly increased with age, being four times higher in patients ages 50 to 64, and 15.5 times higher in those ages 65 years and older. The risk of death was 30% lower in Finland and 8% lower in Sweden when compared with Denmark.
Patients with blood or blood-producing organ diseases, thymoma (thymus tumor), or metabolic diseases had a 65% higher risk of death. Patients with other types of tumors, respiratory diseases, mental or behavioral disorders, and diseases of the circulatory system had also an increased risk of death compared with patients who did not have these comorbidities. There were no differences in the risk of death between men and women.
“These findings are relevant for planning of healthcare resources and highlight an unmet medical need for improved therapeutic management of MG to reduce morbidity and mortality,” the researchers wrote.
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