Increasing incidence of late-onset anti–AChR antibody–seropositive myasthenia gravis

The incidence of myasthenia gravis (MG) from 1970 through 1999 was studied in an area with 2.3 million inhabitants. The mean annual incidence rate of early-onset MG was constant at 3.5 x 10(-6). In late-onset MG, the rate increased from 4.7 to 20.8 x 10(-6). The two onset types of MG may thus be distinct disorders. The author hypothesized that late-onset nonthymoma anti-acetylcholine receptor antibody-seropositive MG may be provoked by environmental factors.