Types of Myasthenia Gravis
Patients with generalized myasthenia gravis have a more severe form of the disease and may experience weakness in other muscle groups. Generalized myasthenia gravis develops in about 50–80% of those who develop eye symptoms. Patients gradually develop difficulty speaking, problems chewing and swallowing, and trouble performing everyday tasks, such as combing their hair or climbing stairs, caused by weakness in the arm and leg muscles.
Congenital myasthenia gravis differs from other forms of MG because it is caused by a genetic defect rather than an abnormal immune system response. Congenital myasthenia gravis is usually inherited in an autosomal recessive pattern, meaning a person must receive a copy of the defective gene from both parents to develop the disease. If a person has only one copy of the defective gene, they will be a carrier but not show any symptoms.
Juvenile myasthenia gravis is the most common of the three types of myasthenia gravis seen in children and adolescents. Juvenile MG, which usually begins before age 18, is a rare, chronic condition that requires lifelong management. Its symptoms — muscular weakness and fatigue — are treatable. And children with the condition — especially those who develop the disease before puberty — may have long stretches without relapses.
For about 15% of patients with myasthenia gravis, the muscles controlling eye and eyelid movement remain the only muscles affected. In these cases, the condition is known as ocular myasthenia gravis. People with symptoms of ocular myasthenia gravis for five years that have not affected other muscles in their body are unlikely to develop weakness elsewhere.
Transient neonatal myasthenia gravis is a rare form of myasthenia gravis that typically affects 10–15% of babies born to mothers who have myasthenia gravis, including those who are symptomatic. During pregnancy, the mother’s autoantibodies can be transferred to her unborn child, resulting in the destruction of fetal acetylcholine receptors. Symptoms usually resolve.