Myasthenia Gravis (MG)

What is it?

• MG is a chronic autoimmune disease that affects the acetylcholine receptors at neuromuscular junctions of voluntary skeletal muscles causing weakness that worsens after periods of activity and improves with rest. Muscles affected generally control eye and eyelid movement, facial expression, chewing, talking, and swallowing. Triggers can include acute or impending illness, pregnancy/postpartum, menstruation, missed medications, or major surgery.

Onset

• Can be sudden and the severity of weakness varies. Women are more affected with earlier onset (20-30 years old) whereas men are more affected with later onset (60-80 years old).

How is it diagnosed?

• Diagnosed using a few different tests. Since weakness is a common symptom of many different disorders, diagnosis may be delayed or missed

  • Physical and neurological exam: assess strength, tone, sensation, coordination, and eye movements

  • Edrophonium test: injection of edrophonium chloride can briefly relieve weakness in people with myasthenia gravis

  • Blood test: to look for elevated levels of acetylcholine receptor antibodies or the presence of the anti-MuSK antibody

  • Electrodiagnostics: repetitive nerve stimulation. Typically in MG, the muscle fibers do not respond well to repeated electrical stimulation.

  • Diagnostic imaging: CT or MRI may identify the presence of a thymoma.

  • Pulmonary function testing: to measure breathing strength

Symptoms

• The hallmark symptom is that weakness is worse after activity but improves with rest. General symptoms include:

  • Ocular myasthenia

  • Ptosis

  • Diplopia

  • Change in facial expression

  • Difficulty swallowing

  • Shortness of breath

  • Dysarthria

  • Weakness of the arms, legs, and neck

Prognosis

• Most individuals can significantly improve their muscle weakness and lead normal or nearly normal lives. Some cases may go into remission (temporary or permanent). Long-lasting remission is the goal of thymectomy and can occur in 50% of individuals.

Treatment

• Focused on reducing and improving overall muscle weakness

  • Thymectomy: The thymus gland is often impaired in individuals with MG. Surgical removal can reduce symptoms and often cure the individual.

  • Monoclonal antibody: Targets the process by which acetylcholine antibodies injure the neuromuscular junction.

  • Anticholinesterase medications: Slow the breakdown of acetylcholine at the neuromuscular junction. This can improve neuromuscular transmission and increase strength.

  • Immunosuppressive drugs: Suppressed the production of abnormal antibodies to improve strength by suppressing the production of abnormal antibodies.

  • Plasmapheresis: blood cleansing procedure in which the plasma antibodies are removed and replaced with albumin or fresh frozen plasma.

  • Intravenous immunoglobulin (IVIG): high-dose plasma protein replacement therapy in which the patient receives intravenous injections of immunoglobulins. This is thought to lower the levels or overall effectiveness of the antibodies that are attacking the nerves.