Diagnosing myasthenia gravis requires a combination of clinical observation, specialized testing, and careful evaluation to distinguish it from other conditions that cause muscle weakness. Early and accurate diagnosis is essential for starting appropriate treatment and preventing complications.

Introduction: Who Should Undergo Diagnostics

If you experience muscle weakness that gets worse with activity and improves with rest, it’s important to see a healthcare professional. This distinctive pattern is one of the hallmark features of myasthenia gravis, which is a condition where communication between nerves and muscles breaks down.^[1]

You should particularly seek medical attention if you notice drooping of one or both eyelids, double vision, or changes in your facial expressions. These symptoms affecting the eye muscles are often the first signs of myasthenia gravis, appearing in more than half of all people who develop the condition.^[1] Other warning signs include difficulty swallowing, changes in speech that make your voice sound soft or nasal, shortness of breath, or weakness in your arms, hands, legs, or neck.^[2]

People of any age can develop myasthenia gravis, though it most commonly affects young adult women under 40 and older men over 60.^[2] The condition can affect approximately 20 out of every 100,000 people worldwide, though the actual number may be higher because some people with mild symptoms may not realize they have the condition.^[3]

It’s especially important to seek immediate medical care if you develop severe breathing difficulties or significant problems swallowing, as these can be signs of a myasthenic crisis, which is a medical emergency. Approximately 15 to 20 percent of people with myasthenia gravis experience at least one myasthenic crisis, and up to half may not be able to identify what triggered it.^[2]

Diagnostic Methods

Diagnosing myasthenia gravis involves several steps and different types of tests. Your healthcare professional will first talk to you about your symptoms, review your medical history, and perform a physical examination. This includes a neurological exam, during which your doctor may test your reflexes, muscle strength, muscle tone, senses of touch and sight, coordination, and balance.^[8]

Ice Pack Test

One of the simplest diagnostic tests is the ice pack test. If you have a droopy eyelid, your healthcare professional might place a bag filled with ice on your eyelid for about two minutes. After removing the bag, they will check whether the eyelid is less droopy. This simple test can provide quick evidence of myasthenia gravis because cooling the muscle temporarily improves its function.^[8]

Blood Tests

A blood test is one of the most important diagnostic tools for myasthenia gravis. The test looks for specific antibodies that interrupt the receptor sites where nerves signal your muscles to move.^[8] In most people with myasthenia gravis, the immune system produces autoantibodies against proteins at the neuromuscular junction, which is the connection point between nerves and muscles.^[3]

The most commonly implicated proteins include nicotinic acetylcholine receptors, muscle-specific kinase (MuSK), and lipoprotein-related protein 4 (LRP4). These proteins are essential for the formation and maintenance of the neuromuscular junction, including the distribution and clustering of the acetylcholine receptors.^[5] The presence of antibodies against these proteins in your blood can confirm the diagnosis of myasthenia gravis.

Nerve Conduction Studies

Your doctor may order a test called repetitive nerve stimulation, which is a type of nerve conduction study. During this test, a healthcare professional attaches small electrodes to the skin over the muscles to be tested. Small pulses of electricity are sent through the nerve going to that muscle to measure whether the nerve can send signals properly.^[8]

The nerve is tested several times to see if its ability to send signals gets worse with repeated use. In people with myasthenia gravis, the muscle response typically decreases with repeated stimulation, which is a characteristic finding that helps confirm the diagnosis. This pattern occurs because the impaired communication at the neuromuscular junction becomes more apparent when the system is stressed by repeated signals.^[8]

Electromyography (EMG)

Another electrical test that may be used is single-fiber electromyography, also called EMG. This test measures the electrical activity traveling between your brain and your muscles. It involves inserting a fine wire electrode through your skin and into a muscle to test a single muscle fiber.^[8] This is a more sensitive test than repetitive nerve stimulation and can detect abnormalities in neuromuscular transmission even in mild cases of myasthenia gravis.

Imaging Studies

Your healthcare professional might order imaging tests such as a CT scan or an MRI to examine your thymus gland. The thymus is a small gland in your chest that is part of the immune system. Approximately 10 percent of people with myasthenia gravis have a thymoma, which is an abnormal growth of the thymus, and this has been linked to the production of autoantibodies.^[5]

Many people with myasthenia gravis have a thymus gland that’s larger than normal, and around 1 in 10 have a thymoma. Identifying whether you have an enlarged thymus or a thymoma is important because it can affect your treatment plan.^[4] These imaging studies help your doctor see the size and structure of your thymus gland and determine whether surgery might be beneficial.

Pulmonary Function Tests

Because myasthenia gravis can sometimes affect the muscles used for breathing, your doctor may order pulmonary function tests. These tests measure whether your condition is affecting your breathing and how well your respiratory muscles are working.^[8] This is particularly important for monitoring your condition and preventing respiratory complications.

The diagnostic process for myasthenia gravis can sometimes take time, as symptoms may be mistaken for other conditions. Some people go years without a correct diagnosis because the symptoms can be subtle or intermittent.^[6] Your doctor may need to rule out other conditions that can cause similar symptoms, such as stroke, multiple sclerosis, thyroid disease, or other neuromuscular disorders.

Diagnostics for Clinical Trial Qualification

When researchers conduct clinical trials to test new treatments for myasthenia gravis, they use specific diagnostic tests and criteria to determine which patients can participate. These qualification standards help ensure that the trial participants have confirmed myasthenia gravis and that the results of the study will be meaningful and applicable to others with the condition.

The classification of myasthenia gravis is important for clinical trial enrollment. Depending on the type of clinical features and the type of antibodies involved, myasthenia gravis can be classified into various subgroups, and each group may respond differently to treatment.^[5]

Common classifications include early-onset myasthenia gravis, where symptoms begin before age 50 and are often associated with thymic hyperplasia, and late-onset myasthenia gravis, where symptoms begin after age 50 and are typically associated with thymic atrophy. There is also thymoma-associated myasthenia gravis, ocular myasthenia gravis where symptoms affect only the eye muscles, and myasthenia gravis with anti-MuSK antibodies.^[5]

For enrollment in most clinical trials, participants typically need to have a confirmed diagnosis through positive antibody tests. Blood tests showing the presence of antibodies against acetylcholine receptors, MuSK, or LRP4 are standard requirements. These tests help researchers ensure that participants have the autoimmune form of myasthenia gravis that the experimental treatment is designed to address.

Clinical trials may also require specific results from nerve conduction studies or electromyography tests. These electrical studies provide objective evidence of impaired neuromuscular transmission, which is the underlying problem in myasthenia gravis. Researchers use these tests not only to confirm the diagnosis but also to measure how severe the condition is before treatment begins.

Imaging studies showing the status of the thymus gland may also be required for certain clinical trials, particularly those testing treatments related to thymectomy or therapies that might work differently depending on whether a person has a thymoma. CT scans or MRI scans of the chest are commonly used to evaluate the thymus.

Many clinical trials use standardized rating scales to assess the severity of myasthenia gravis symptoms. These scales help researchers measure whether a treatment is working by comparing symptoms before and after treatment. Participants may need to score within a certain range on these scales to be eligible for a trial. The scales typically evaluate muscle strength in different parts of the body, including the eyes, face, throat, arms, and legs.

Pulmonary function testing is often required for clinical trial participation, especially for trials testing treatments for more severe or generalized myasthenia gravis. These tests help researchers identify participants who have respiratory muscle weakness and ensure that participants are stable enough to safely participate in the trial.

Clinical trials may have specific requirements about current treatments. For example, some trials enroll only people who haven’t responded well to standard treatments, while others may require that participants be on stable doses of certain medications for a specified period before joining the trial. Documentation of previous treatments, including medications tried and their effectiveness, is typically required.

Additional laboratory tests that may be required for clinical trial qualification include complete blood counts, kidney function tests, and liver function tests. These help researchers ensure that participants are healthy enough to safely receive the experimental treatment and that they don’t have other conditions that might interfere with the study results.