Incidence and clinical feature of Myasthenia gravis: A five-year data analysis in Ulaanbaatar, Mongolia

Myasthenia gravis (MG) is a rare neuromuscular disorder. Till now, there are no studies on the prevalence and incidence of MG in Mongolia. The current study aimed to elucidate the incidence of MG in Ulaanbaatar, the age of onset, and the gender distribution of Mongolian patients with MG. We conducted a cross-sectional, hospital-based study involving MG patients (n=48) all around Ulaanbaatar from 1 January 2015 to 1 January 2020. The clinical diagnosis was assessed with the Myasthenia Gravis Foundation of America (MGFA) classification system. The disease severity was evaluated by using Osserman’s classification. The diagnosis was confirmed with serological and electrophysiological tests. Statistical analysis was performed using SPSS software. A total of 30 patients with MG were registered for the last five years in Ulaanbaatar. The average annual incidence of MG in Ulaanbaatar was 0.65 per 100,000 populations (95%CI 0.26-1.34), 0.60 in males (95%CI 0.25-1.28), and 0.69 in females (95%CI 0.33-1.46). The cumulative incidence in the study period was 3.2 per 100,000 populations. The ratio of males to females was 1:1,3. The median age for onset of MG was 33 years (ranging from 27 to 46 years); 43.3% of patients had ocular and 56.7% generalized symptoms at the disease onset. Only 23.3% of patients remained with purely ocular symptoms (Osserman I stage). The average incidence of MG between 2015 and 2020 was 6,5 per 1.000.000 population, and the annual incidence was relatively stable. Although ocular and generalized symptoms were observed each in about half of the cases, only one-fourth remained with pure ocular signs at the end of the review period.