Diagnosing Myasthenia Gravis: What Methods Can Be Used?

Doctor talking to a patient

Story at-a-glance -

  • Diagnosing myasthenia gravis can be difficult. It’s believed that the diagnosis can often be delayed by months, or even years, due to muscle weakness being a potential symptom of many other diseases
  • Before jumping into any specific test, your doctor will ask you certain questions and review your medical history

Diagnosing myasthenia gravis can be difficult. It’s believed that the diagnosis can often be delayed by months, or even years, due to muscle weakness being a potential symptom of many other diseases.

The situation becomes even more complicated if the symptoms are mild, and only certain muscles are affected. Fortunately, there are several methods your doctor can use to help reach an accurate diagnosis.1

Preparing for Your Diagnosis

Before jumping into any specific test, your doctor will ask you certain questions and review your medical history. If they notice a pattern that highly suggests myasthenia gravis, they will proceed to simple physical tests that will examine your:2

Reflexes

Muscle strength

Muscle tone

Senses of touch and sight

Coordination

Balance

Edrophonium Test

The edrophonium test (also called the Tensilon test) is usually one of the first tests conducted to confirm the presence of myasthenia gravis. You will be injected with edrophonium chloride to provide temporary relief from muscle weakness. The effect is often sudden, which can help determine the presence of the disease.3

Edrophonium is a chemical that blocks certain antibodies destroying acetylcholine, the neurotransmitter responsible for sending signals to your muscle receptor sites.4

Electrodiagnostic Testing or Electromyogram

An electromyogram (EMG) examines the functionality of your muscles and nerves. Tiny needles are inserted into your muscles and nerves, which will be stimulated by sending electrical impulses. If your muscles do not respond positively to the exam, it can be considered an indicator of myasthenia gravis.5 There are two EMG tests your doctor can use:6

Repetitive nerve stimulation (RNS): The muscles will be subjected to repeated nerve stimulations to test for responsiveness. Gradually decreasing responsiveness after consecutive stimulations is usually detected in people with myasthenia gravis.

Single Fiber EMG (SFEMG) with axonal micro-stimulation: You will make a small muscular contraction with a single fiber electrode attached to measure neuromuscular function.

Blood Tests for Specific Antibodies

Three blood tests are usually performed to supplement the other diagnostic tests for myasthenia gravis:7

Acetylcholine Receptor Antibody test: This test specifically measures the levels of this antibody in your blood. Approximately 85 percent of patients with myasthenia gravis have abnormal levels of it.

Anti-MuSK Antibody test: If you tested negative for acetylcholine antibodies, this test will look for anti-MuSK (anti-muscle-specific kinase8) antibodies. It’s estimated that 40 percent of people who tested negative for acetylcholine antibodies have anti-MuSK antibodies instead.

Thyroid function testing: You may need to have your thyroid levels checked, because thyroid disease can exhibit symptoms similar to myasthenia gravis. Many people with the disease have thyroid problems as well.9

Ice Pack Test

This is a simple test done if myasthenia gravis is affecting your eyelids. Your doctor will place an ice pack on the affected eyelid for five minutes, and any improvements will be monitored afterwards. The cold temperature decreases the breakdown of the acetylcholine neurotransmitter, restoring temporary control of the affected muscle for testing purposes.10

Imaging Tests

You may have to undego an X-ray exam, computerized tomography (CT) scan or a magnetic resonance imaging (MRI) scan to check for possible tumors or abnormalities, especially in your thymus gland.11

Pulmonary Function Tests

Pulmonary function tests may be conducted to test for the strength of your breathing muscles. If these muscles are weak, they can lead to myasthenic crisis, which is a breathing difficulty that requires immediate treatment. You will need to breathe into a mouthpiece, and a computer will record the amount of air you can breathe, helping doctors determine if your lungs are affected or not.12

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