How Myasthenia Gravis Is Diagnosed

Myasthenia gravis (MG) is an autoimmune disease that affects the neuromuscular system, which regulates bodily motion, swallowing, and breathing. In this neuromuscular disorder, the body’s own immune system interrupts signaling between nerves and muscles, leading to muscular weakness, especially after exertion, as well as respiratory issues and a host of other symptoms.

Since there are many different signs and they may be subtle, diagnosis can be challenging. It may involve everything from function and blood tests, as well as those assessing nerve and pulmonary function.

Self-Checks

Because of its often subtle, fluctuating symptoms, MG is notoriously difficult to diagnose. Typically, symptom onset is rapid, and severity can vary, with most people reporting that they feel stronger in the morning and weaker as the day goes on. The first step involves recognizing its signs and making the decision to get medical help.

Myasthenia gravis can be characterized by any number of the following:

• Generalized muscle weakness: One of the hallmarks of the condition is muscle weakness and fatigue in the limbs and neck following periods of activity. This can resolve after periods of rest.
• Ocular myasthenia: This drooping of one or both eyelids is often the first symptom, and 80% of those who have it develop full-blown MG. This occurs due to weakness of the muscles there.
• Diplopia: Blurred or double vision is another common sign of MG, especially when occurring alongside other symptoms. Certainly, visual problems of this nature warrant medical help.
• Altered facial expressions: Muscle weakness in the face can cause permanent changes to the appearance of the face at rest as well as typical facial expressions. 
• Swallowing difficulties: Since the muscles of the throat are part of the neuromuscular system, MG can also cause difficulty swallowing. Related to this is slurring while speaking, a condition called speech dysarthria.
• Breathing difficulties: Some cases of MG weaken the muscles necessary for breathing, causing serious respiratory difficulties. In severe cases, respiratory failure can follow, which is a medical emergency.

If you experience any of the above, it’s worth seeking out medical attention to get a fuller picture of what’s happening.

Physical Examination

Medical diagnosis of myasthenia gravis requires assessment of how the symptoms are presenting, as well as other important information about current health status. Typically, this entails looking at:

• Medical history: Getting a sense of any past health issues you’ve had, as well as what medications or supplements you’re currently taking, is a crucial first step in clinical diagnosis.
• Symptoms and physical health: Alongside consideration and assessment of symptoms, your overall health is a standard part of diagnosis. This means measurements of things like heart rate, blood pressure, and pulse.
• Respiratory evaluations: Since lung function can so often be affected by MG, doctors will listen to your lungs at work and use other tests to assess how well you are breathing.
• Functional testing: Function and muscular response tests can provide a picture of the severity of any neuromuscular effects. Through a series of tests, doctors assess how well you perform motor tasks, how well coordinated your eye movements are, and how well you sense touch, among other measures.  
• The ice pack test: For those with ocular myasthenia, another physical test involves having patients apply ice packs to the eyes, or asking them to spend a couple of minutes with their eyes closed in a dark room. Improvements in drooping after the test can be a sign of MG.

Assessing Risk Factors

During initial evaluations for suspected myasthenia gravis, it will also be worth assessing how much risk you have for developing MG. While its exact causes are unknown, we do know a good deal about who is at most risk.

In an effort to tease out these risk factors, doctors will ask about:

• Age and sex: Although MG can occur in both sexes, and it can arise at any age, it’s most commonly seen in women ages 20 to 40 and men between 50 and 80 years old.
• History of autoimmune illness: Doctors will ask about previous or current health conditions, as those who have had or have rheumatoid arthritis and lupus may be more at risk.  
• Previous/current medications: Risks increase when you’ve taken medications for malaria (chloroquine or mefloquine) or heart arrhythmias (beta-blockers), certain antibiotics (including doxycycline and erythromycin), as well as several psychiatric drugs.  
• Previous surgeries: Those who have undergone extensive surgery in the past are at a higher risk of developing this autoimmune disorder.
• History of thyroid disease: Among the potential effects caused by problems with the thyroid gland is a higher risk of MG. 

Labs and Tests

The only way to conclusively identify a case of myasthenia gravis is to perform clinical testing, imaging, and lab work. As with other autoimmune diseases, doctors look for the presence of specific physiological markers and assess the severity of the disease. Diagnosis of this disease will involve a combination of methods.

Blood Tests

Principally, doctors measure the amount of acetylcholine receptor antibodies in blood, with higher levels often being signs of MG. This antibody hinders the activity of acetylcholine, which motor nerves emit to coordinate muscle contractions. Presence of another antibody, anti-MuSK, can also be a sign; however, some with MG have none of these antibodies, so blood tests may not be conclusive.

Edrophonium Test

This test, most often used to test eye muscles, involves injections of edrophonium chloride, a drug that boosts acetylcholine levels by preventing it from being broken down by the body. Those with MG will experience improved function and mobility, with less fatigue.

Electromyogram (EMG)

EMG measures the activity of muscles and nerves and can assess the extent of neuromuscular damage; it's considered the most sensitive test for myasthenia gravis. Its first stage involves recording nerve activity while mild electricity is applied to the area. In a second test, a tiny needle is inserted into a muscle to record how well nerves are communicating, and overall health of the muscle, as you perform tasks and at rest.

Imaging Techniques

If myasthenia gravis is suspected, techniques like magnetic resonance imaging (MRI) or computed tomography (CT) scans may be employed to assess the thymus gland. This gland helps the body develop immune function, grows throughout puberty, and then shrinks and disappears in adulthood. In MG, it remains large and can develop thymomas (tumors), which are detected with imaging.

Differential Diagnosis

Since weakness and the other symptoms of myasthenia gravis occur in other conditions—and since milder cases may impact only a few muscles—this disease is often missed or not detected initially. It shares features with several other conditions:

• Lambert Eaton myasthenic syndrome: In this rare autoimmune disorder, the immune system attacks channels that regulate calcium levels in the blood. This causes insufficient acetylcholine to be released, leading to muscle weakness, fatigue, and other symptoms.
• Stroke: The ocular effects of myasthenia gravis, such as drooping and muscle weakness, can also arise in cases of stroke. This is especially the case if the stroke affects the brain stem or nerve centers associated with the eyes.     
• Graves’ disease: This malfunction of the thyroid shares some symptoms with MG, and the two are sometimes mistaken for one another in the clinic. In particular, both diseases affect eye movements. That said, the two conditions can occur concurrently as well.
• Congenital myasthenia: Though similar in effects, congenital myasthenia is an inherited disorder rather than an autoimmune disease like MG. In these cases, genetic mutations lead to insufficient levels of acetylcholine.     

A Word From Verywell

While it can be concerning to feel fatigue, muscular weakness, and the other symptoms of myasthenia gravis, it’s important to remember that this disease is relatively rare. Only about 14 to 40 in every 100,000 people are estimated to have it. That said, make sure to talk to your doctor or seek care if you’re concerned.  

Though disruptive, myasthenia gravis is also highly manageable, and, with treatment, most with the condition are able to lead healthy, happy lives. Essential in the process of taking this disease on is proper detection and diagnosis. And that starts with being vigilant and staying informed; it starts with you.