Prevalence, Incidence, and Mortality of Myasthenia Gravis and Myasthenic Syndromes: A Systematic Review

Abstract

Introduction: No systematic reviews were published in the last years investigating epidemiological data, involving myasthenia gravis (MG) and related myasthenic syndromes. This systematic review aimed to estimate the prevalence, incidence, and mortality of all MG types and myasthenic syndromes worldwide.

Methods: All literature published up to February 2024 was retrieved by searching the databases "Medline," "Embase," "ISI Web of Science" and "CINAHL" using the following search terms: (epidemiolog* OR frequency OR prevalence OR incidence OR mortality) AND (myasth* OR "anti-acetylcholine receptor antibody" OR "AChR" OR "MuSK" OR "anti-muscle specific kinase antibody" OR "LRP4" OR "seronegative MG").

Results: A total of 94 studies, performed between 1952 and 2022, were included. Prevalence of MG ranged from 20 to 475 cases per million, with a mean prevalence of 173.3 (95% confidence interval [CI]: 129.7-215.5) cases per million and a median prevalence of 129.6 cases per million. Incidence rates ranged from 2.3 to 61.3 cases per million person-years, with a mean incidence of 15.7 (95% CI: 11.5-19.9) and a median of 13.3 cases. Mortality rates showed a mean of 1.4 (95% CI: 0.8-2.1) cases per million person-years. Acetylcholine receptor (AChR)-MG was the clinical subtype more frequent in terms of prevalence and incidence.

Discussion: The prevalence and incidence of MG have significantly increased over the last years worldwide, probably due to the improvement of epidemiological methodologies and current advances in diagnosis. However, we observed a significant variation in frequencies of MG between and within countries because of methodological biases and complex heterogeneity of the disease characterized by several phenotypes and different clinical responses.

Keywords: Epidemiology; Incidence; Mortality; Myasthenia gravis; Prevalence.

Fig. 1.

PRISMA flow diagram of the included study.

Fig. 2.

Geographical distribution of the included studies. This figure offers an overview of the geographical distribution of the included studies. The gradient of blue indicates the number of studies: countries represented with darker blue are those with a higher number of studies. The gray countries are those without studies.

Fig. 3.

Crude PRs per million reported by ALL MG studies over time. This figure reports the crude prevalence (per million) of every study that examined the prevalence of ALL MG. The years refer to the last year/period investigated by the study.

Fig. 4.

Crude IRs per million person-years reported by ALL MG studies over time. This figure reports the crude incidence (per million person-years) of every study that examined the incidence of ALL MG. The years refer to the last year/period investigated by the study.

Fig. 5.

Crude MRs per million person-years of the studies examining ALL MG. This figure reports the crude mortality (per million person-years) of every study that examined the mortality of ALL MG. The years refer to the last year/period investigated by the study.

Fig. 6.

Number of males and females in ALL MG studies over the years. This figure depicts the sex distribution (in percentage) in the ALL MG studies over the years. The year of the study refers to the last year examined by the studies. In brackets, the number of studies reporting these data for each year.

Fig. 7.

Mean age of ALL MG cases over the years, stratified by sex. This figure illustrates the mean age of MG cases stratified for sex, over the years. The year of the study refers to the last year examined by the studies. In brackets, the number of studies reporting these data for each year.