Learn The BasicsThe term prognosis refers to the likely course of a medical condition. Like with many other autoimmune diseases, myasthenia gravis (MG) occurs in bouts of worsened symptoms or flare-ups followed by periods of remission in which symptoms disappear.
Usually, the symptoms of MG are most severe one to three years after it’s first diagnosed.
Many factors may affect the prognosis of MG, including course of treatment, age of disease onset and disease subtype.
How treatment affects prognosis
The main factor affecting disease prognosis in MG is treatment. If the disease is left untreated, a serious complication called a myasthenic crisis may develop. This is characterized by extreme muscle weakness, mainly affecting the diaphragm and other muscles used for breathing. It can lead to shallow and ineffective breathing and be life-threatening.
In the last 50 years, the mortality rate due to myasthenic crisis went from 50 to 80% down to as little as 4.5%, thanks to more proactive diagnosis and treatment.
Age of disease onset and prognosis
MG can either be early-onset, in which symptoms appear before age 50, or late-onset, in which symptoms appear after age 50.
Research has shown that disease onset before age 40, together with extended thymectomy or the removal of the thymus and the administration of high-dose prednisolone, a corticosteroid that works by dampening the immune system, given on alternating days, are associated with a reduced risk of MG relapse.
Another study found that late age of disease onset, together with high concentrations of anti-acetylcholine receptor (AChR) antibody in the blood and the presence of a thymoma or cancer of the thymus, seems to be associated with the generalization of MG.
Prognosis by disease type
MG may be caused by the presence of autoantibodies against the AChR or another protein called muscle-specific kinase, or MuSK, at the neuromuscular junction, the connection between nerve and muscle cells.
Research has shown that anti-MuSK antibody-associated MG tends to be more severe and progress more rapidly than anti-AChR-associated MG. Early myasthenic crises are also more common in anti-MuSK antibody-associated MG.
Life expectancy
With treatment, the life expectancy of a person with MG is the same as that of a person not affected by the disease.
According to the Centers for Disease Control (CDC), the life expectancy of the general U.S. population was 77.5 years in 2022. For men, it was 74.8 years, while for women it was 80.2 years.
Survival rates
A large Danish study published in 1998 showed that the crude annual mortality rate, or the number of deaths, was 1.8 per million people. The annual mortality rate due to MG was 1.4 per million.
The study also reported that mortality rates due to MG were low below age 50 and that they increased each year after that, for both men and women. After age 60, mortality rates due to MG increased more rapidly in men than in women.
The overall survival rate was 85% three years after diagnosis, 81% five years after diagnosis, 69% 10 years after diagnosis and 63% 20 years after diagnosis.
Reviewed by Debjyoti Talukdar, M.D., on June 6, 2025.