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Myasthenia Gravis and Differential Diagnosis

Reviewed by: HU Medical Review Board | Last reviewed January 2023

Myasthenia gravis (MG) is an autoimmune condition. This means it is caused by the immune system attacking the body mistakenly. The symptoms of MG can sometimes look like other conditions. In some cases this can make it difficult to diagnose. As part of the process of diagnosing you, your doctor may create a differential diagnosis.1,2

What is a differential diagnosis?

A differential diagnosis is a list of the possible conditions that could cause your symptoms. It is not an official diagnosis, but a list of possible diagnoses.2,3

Some conditions can be diagnosed with a single test. But many other conditions require multiple tests for diagnosis. Some conditions have symptoms that overlap with common symptoms of MG.1,2

The most common symptom of MG is muscle weakness. This weakness tends to impact the face and eyes. But many other conditions also cause muscle weakness. This can sometimes make it hard to identify the cause of your muscle weakness.1-3

How does a doctor make a differential diagnosis?

The process of making a differential diagnosis typically includes a physical exam and health history. You also may receive lab testing, such as a blood test. And your doctor may request imaging, like an MRI (magnetic resonance imaging).2-4

The health history will include questions about your symptoms and medical history, such as:2-4

  • What are your symptoms?
  • How long have you had these symptoms?
  • Has there been any change in your symptoms over time?
  • Do your symptoms change throughout the course of the day?
  • Have you noticed anything that triggers your symptoms or makes them better?

What might be the differential diagnosis for MG?

Other conditions that have symptoms that can overlap with MG symptoms include:

Lambert-Eaton syndrome

Lambert-Eaton syndrome causes muscle weakness. But unlike MG where weakness gets worse with prolonged use of muscle, weakness in Lambert-Eaton gets better with exercise. This syndrome is sometimes caused by an underlying condition like cancer.1

Blood clot in the sinuses

This can be a serious condition. A blood clot in the sinuses is also called cavernous sinus thrombosis. These clots can cause similar symptoms in the eye muscles as MG, resulting in double vision. But in the case of a blood clot, symptoms usually begin suddenly and can include other symptoms such as:1,5

  • Sensory loss on the face
  • Vision loss
  • Headache

Multiple sclerosis (MS)

Multiple scleorsis, like MG, is an autoimmune disorder. But MS is caused by the immune system targeting the protective cover on nerves in the brain and spinal cord. MS can cause weakness, but also can cause vision loss, sensory symptoms, and bowel and bladder dysfunction. MS is treated differently than MG.1


Botulism is an illness that causes weakness in the same face muscles as MG, at least initially. It usually comes from eating contaminated foods. Symptoms develop very quickly. Botulism causes descending paralysis that starts in the face and then spreads to the arms and shoulders, torso, and then possibly the legs. This is an emergency.1

Lyme disease

Tick-borne diseases like Lyme can cause muscle weakness and difficulty breathing. But Lyme disease can also cause symptoms that are not linked to MG, like rash and fever.1,6

Polymyositis and dermatomyositis

These 2 conditions are rare. Both cause muscle inflammation and weakness. The weakness gets worse over time and can cause trouble breathing.1,7

Amyotrophic lateral sclerosis (ALS)

ALS is also called Lou Gehrig’s disease. Weakness typically starts in one limb and over time worsens and spreads, leading to severe muscle weakness all over the body. This can lead to difficulty breathing and ultimately death.6

Narrowing down a diagnosis

The differential diagnosis is just one step in the diagnosis process. After your first visit with your doctor and differential diagnosis, you may have follow-up tests or exams. These studies will help narrow down the differential diagnosis. In most cases this will all lead to an official diagnosis. After your official diagnosis, you and your doctor can focus on treatment and management.1-3

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