Supplementary Material for: A Prospective Study of the Incidence of Myasthenia Gravis in the East Midlands of England

Objectives: A number of worldwide studies have highlighted a rising incidence of myasthenia gravis (MG) over the past few decades. This is largely due to an increase in numbers in older patients. To establish whether this was a consistent finding in the United Kingdom, we conducted a large, 4-year prospective cohort study of all known patients with new-onset MG in the East Midlands of the United Kingdom. Methods: Between 2014 and 2018, all 120 patients with a new diagnosis of MG who were residing in the East Midlands were enrolled. Results: Median age at disease onset was 63 years (78% aged over 50 years) and most patients (57%) were male. The average annual incidence rate (IR) was 17.6/1,000,000 (95% CI 10.7–28.6). IRs remained stable between 2014 and 2018 except for rising IRs in patients over 65 years of age (p value for trend, <0.001). Conclusions: Twenty years after the last comprehensive prospective incidence survey of MG in the east of England, we have demonstrated a rising incidence. The greatest increases seen were in patients over 65 years. Given the rigorous study methods employed, future replicate prospective studies from the same region will establish whether these rising figures are due to biological factors, independent of improved case ascertainment.