Myasthenia Gravis

Diagnosis

Mayo Clinic doctors who have training in nervous system conditions (neurologists) and other specialists work closely as a team to diagnose myasthenia gravis. In Mayo Clinic's system, doctors usually can complete your testing and diagnosis within two or three days and develop your treatment plan soon after diagnosis.

Mayo Clinic offers many resources to thoroughly test and accurately diagnose people for myasthenia gravis, including an electromyography lab, an immunologic lab and a muscle research laboratory.

Your doctor will perform a thorough physical exam and review your symptoms, including signs of muscle weakness that improve with rest. Your doctor will review your medical history. In the physical exam, your doctor may test your reflexes, muscle strength and tone, senses of touch and sight, gait, posture, coordination, balance and mental skills. Your doctor and other specialists also may conduct several tests to diagnose myasthenia gravis.

• Blood analysis. A blood test checks for the abnormal antibodies in myasthenia gravis that may be blocking your muscle receptors from nerve signals.
• CT scan. In this imaging test, your doctor checks the thymus gland for enlargement or the presence of a tumor in the thymus gland (thymoma).
• Edrophonium test. Your doctor injects a chemical (edrophonium) into your bloodstream. Sudden but temporary improvement of muscle strength can indicate myasthenia gravis.
• Electromyography (EMG). Electromyography (EMG) measures electrical activity within muscles or individual muscle fibers (single-fiber EMG).
• Nerve conduction studies. Nerve conduction studies measure the strength of muscle contraction by stimulating nerves with a small electrical impulse applied to your skin. The application of repeat impulses can reveal specific muscle weakness.
• Pulmonary function tests. These tests indicate whether myasthenia gravis affects muscles that help you breathe (respiratory muscles).

Read more about CT scan and electromyography at MayoClinic.com.