Tests For Myasthenia Gravis

Myasthenia gravis (MG) is diagnosed using a combination of a health history, physical exam, and a variety of tests. The tests used include strength tests (called pre-testing or bedside tests), electrical studies, blood work, and imaging tests.

Physical exam

Pre-testing (also called bedside testing) includes a complete physical exam. This includes tests for:1,2

  • Muscle strength, especially in the head and neck
  • Vision, eye movement, and eyelid movement
  • Breathing and lung function

These bedside tests should be repeated with every follow-up appointment to track any changes. However, MG muscle weakness can change day-to-day and over time, so results may be quite different from one appointment to the next.1,2

Strength tests

Your doctor will ask you to perform a series of movements to test your muscle strength. Examples of muscle strength tests include:2,3

  • Looking up for 1 to 3 minutes
  • Keeping the eyes tightly closed while the doctor tries to open them
  • Looking sideways for 1 minute
  • Holding the arms out for 2 minutes
  • Doing deep knee bends with a straight back
  • Counting out loud from 1 to 50 with multiple breaths
  • Counting out loud with 1 breath
  • Making a high-pitched “eeeee” sound
  • Holding 1 leg up for 3 minutes while laying down
  • Rising from a chair without using the arms, up to 20 times
  • Trying to smile, whistle, suck through a straw, or blow up a balloon

These movements are designed to cause muscle weakness in the eyes, face, jaw, neck, throat, arms, or legs. How quickly an eye begins to droop or how long someone can hold up their leg gives the doctor an idea of which muscle groups are affected and how mild or severe the MG is.2

Here is where muscle weakness is most often found:3

  • Eyes only – 17 percent
  • Eyes and any other muscles – 50 percent
  • Eyes, face, and neck – 13 percent
  • Eyes, arms, and legs – 20 percent

Ice pack test

An ice pack test may be performed in people with droopy eyelids. With this test, an ice pack is placed on the closed eyelid for a few minutes. If the droopiness gets better when the ice pack is removed, it may suggest MG. The results of this test can be unreliable, so it is not always performed. Other tests will still be needed to confirm MG.1

Electrical studies

Your doctor will perform tests to measure how fast and how strong the electrical activity is between your nerves and muscles. These tests are called electrodiagnostic studies. These tests include:1

  • Nerve conduction studies (NCS)
  • Repetitive nerve stimulation (RNS) tests
  • Electromyography (EMG)
  • Single-fiber electromyography (SFEMG)

Nerve conduction studies (NCS) tell the doctor how fast and how strong the electrical activity is in your nerves and neuromuscular junction. Repetitive nerve stimulation (RNS) is one part of the NCS and is often used for people with generalized MG. It is not as accurate in people with ocular MG.1

Electromyography (EMG) is an electrical test of your muscle cells. Together, the NCS and EMG tests give your doctor a picture of the health and function of your nerves, muscles, and their communication.1

An even more sensitive test, called single-fiber electromyography (SFEMG), may be needed for some people. SFEMG is more complicated and not as widely available.1

No longer used

The Tensilon, or edrophonium test, is no longer used in the United States and many other countries. Antibody testing is more reliable. The edrophonium test had high rates of false positives and other complications.1

Other tests that will be needed to diagnose myasthenia gravis include:1

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Written by: Jessica Johns Pool | Last reviewed: May 2021