Causes and Diagnoses

Causes and Diagnoses of Myasthenia Gravis

The cause of myasthenia gravis is not completely understood at this time, but it is likely it is related to a disorder of the thymus gland. Researchers believe that the thymus gland may give incorrect instructions to developing immune cells, leading to the creation of acetylcholine receptor antibodies and causing the autoimmune disorder.

The thymus gland, which is located in the chest beneath the breastbone, plays an important role in your immune system development. Starting out large in infants, it grows gradually until puberty, when it starts getting smaller. The gland is eventually replaced by fat as you age.

In adults with the myasthenia gravis, however, the thymus gland remains large and contains clusters of immune cells that indicate an active immune response.

People with myasthenia gravis sometimes develop thymomas (tumors of the thymus gland). While thymomas are usually benign, they can become cancerous.

Diagnosing myasthenia gravis

Diagnosis is often delayed if symptoms are mild, or if muscle weakness is confined only to a few areas. Your physician will review your medical history and conduct neurological examinations, with particular attention to eye movements or muscle weakness.

Other tests may include:

• Acetylcholine receptor antibody test: This blood test looks for antibodies to the neurotransmitter acetylcholine. Most patients with the disease have abnormally elevated levels of these antibodies.
• Anti-MuSK antibody test: This blood test looks for anti-MuSK antibodies in patients who have a negative acetylcholine receptor antibody test.
• Nerve conduction tests: These tests measure and record muscle response through electrical nerve stimulation.
• Single-fiber electromyography (EMG): This test measures the electrical potential of muscle fibers stimulated by electrical impulses. People with myasthenia gravis do not respond well to such electrical stimulation.