Myasthenia gravis (MG) is a condition involving the neuromuscular junctions, or connections between nerves and muscles. However, many other diseases can cause similar symptoms, such as muscle weakness in the eyes, throat, and limbs. Because of this, doctors need to make sure MG is the right diagnosis by ruling out other conditions first. This process is called differential diagnosis.

Figuring out the correct diagnosis can take time. Doctors carefully check for other possible causes before confirming MG and starting treatment of myasthenia gravis. Below are some conditions your doctor may consider and test for, based on your symptoms.

If You Have Eye and Vision Symptoms

The first symptoms of myasthenia gravis are usually ocular — related to the eye and vision. In fact, about 85 percent of people with myasthenia gravis first experience ocular symptoms, such as ptosis (drooping eyelid) and diplopia (double vision). Other conditions can also cause these symptoms and need to be ruled out before diagnosing MG, such as ocular myasthenia gravis or generalized myasthenia gravis.

1. Thyroid Eye Disease

Thyroid eye disease (TED) is an autoimmune disease, meaning the immune system mistakenly attacks the body’s own tissues. In TED, the tissues around the eye are targeted. Symptoms can include double vision and other eye issues, such as irritated or dry eyes, pain with eye movement, bulging eyes, and difficulty closing the eyelids. TED may improve on its own, but some cases require treatment.

TED is more common in females, according to Cleveland Clinic, and most people are diagnosed in their 40s. Doctors diagnose TED using blood tests and, if needed, imaging tests such as a CT scan, MRI, or ultrasound.

2. Oculopharyngeal Muscular Dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is a rare genetic disease (a condition that runs in families) caused by a problem with a protein called polyadenylate-binding protein. In OPMD, muscle cells die due to a buildup of this protein, leading to weakness in the muscles of the throat and upper eyelids. Symptoms may include drooping eyelids, swallowing issues, and weakness in muscles of the face, legs, and arms.

OPMD usually develops between ages 40 and 60. Diagnostic testing may include blood tests, muscle biopsy, and electromyography (EMG), which checks muscle and nerve function.

3. Chronic Progressive External Ophthalmoplegia

Chronic progressive external ophthalmoplegia (CPEO) is a genetic disorder caused by defective mitochondria, the parts of cells that produce energy. CPEO leads to gradual eye muscle weakness that gets worse over time. Drooping eyelids are usually the first sign. Other symptoms may include weak or paralyzed eye muscles, weak arms and legs, and problems swallowing.

CPEO is most common in adults under 40. To make the diagnosis, doctors use genetic testing and muscle biopsy (removing a small amount of tissue to be examined in a lab).

4. Third Nerve Palsy

Third nerve palsy — also called cranial nerve 3 (oculomotor) palsy — affects the nerve controlling eye movement and eyelid function, causing drooping eyelids and double vision. Other signs include abnormal eye alignment and an enlarged pupil (black center) that doesn’t react to light by getting smaller.

Third nerve palsy is most common in people over 60. Blood tests and imaging, like MRI, may be used for diagnosis.

5. Horner’s Syndrome

Horner’s syndrome — also called Bernard-Horner syndrome or oculosympathetic palsy — is caused by damage to a nerve in the head and neck. This condition is often a sign of another underlying medical problem, such as a tumor, stroke, or injury. Horner’s syndrome affects just one side of the face and may cause:

• Drooping of the upper eyelid
• A smaller pupil in one eye
• A sunken appearance of the eye
• A higher-than-normal lower eyelid (called “upside-down ptosis”)
• Delayed or smaller pupil changes in dim lighting

Horner’s syndrome can be diagnosed using a pupil dilation test.

6. Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease that causes the immune system to attack the nervous system. These attacks damage myelin (the protective covering around nerve fibers), disrupting communication between the brain and muscles. If the eye muscles are affected, symptoms can include double vision, uncontrolled eye movements, and vision loss.

MS is twice as common in females as in males, according to the National Organization for Rare Disorders (NORD), and is usually diagnosed between ages 20 and 50. Testing to diagnose MS may involve MRI scans, optic nerve tests, and a lumbar puncture (spinal tap).

If You Have Face and Throat Symptoms

About 15 percent of people with myasthenia gravis first experience bulbar symptoms, which affect the face and throat and include facial drooping, dysphagia (trouble swallowing), and dysarthria (trouble speaking). However, other conditions can also cause these symptoms.

If you have weakness in your face, throat, or neck, your doctor may consider testing you for the conditions listed below.

7. Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) — also called Lou Gehrig’s disease — affects the nerves that control muscles. ALS occurs when cells in the brain and spinal cord break down over time, leading to muscle weakness. Early symptoms include difficulty swallowing and speaking, weakness in one arm or leg, and muscle twitching.

ALS is more common in adults in their 60s, 70s, and 80s. To diagnose ALS, doctors may use blood tests, MRI scans, or a spinal tap.

8. Lyme Disease

Lyme disease is an infection caused by bacteria from a deer tick bite. Symptoms can appear as early as three days or as late as 30 days after the bite. The hallmark clinical feature of Lyme disease is a bull’s-eye-shaped rash — a key distinguishing characteristic. Other common symptoms include headache and fatigue. If Lyme disease goes untreated, it can lead to facial muscle weakness that may look like facial drooping.

Lyme disease is more common in certain parts of the United States, including the Northeast, the upper Midwest, mid-Atlantic states, and northern California. Doctors diagnose Lyme disease using a blood test that detects antibodies (protective proteins made by the immune system).

9. Miller Fisher Syndrome

Miller Fisher syndrome, a rare autoimmune condition, is a type of Guillain-Barré syndrome (GBS) that affects the nerves, often after an infection. (GBS is discussed in more detail below.) Facial nerves are commonly affected first. Symptoms may include double vision, drooping eyelids, facial paralysis, and problems with eye movement.

According to Cleveland Clinic, Miller Fisher syndrome is most common in adults older than 55, males, and people of Asian descent. Diagnosis may include blood tests, nerve conduction tests, or EMG.

10. Botulism

Botulism is a serious condition caused by a toxin (botulinum) that attacks the nerves, leading to muscle weakness. Bacteria produce the toxin, which can contaminate food, especially improperly canned products. Signs and symptoms include:

• Drooping eyelids
• Double or blurry vision
• Difficulty swallowing
• Trouble speaking
• Problems with eye movement
• Breathing difficulties

If you have symptoms of botulism, you should see your doctor immediately or go to the emergency room.

If You Have Limb Weakness

Some people with myasthenia gravis also experience weakness in their arms or legs. However, limb weakness alone affects only about 5 percent of people with MG. When this symptom does occur, it’s usually along with eye or throat symptoms.

11. Lambert-Eaton Syndrome

Lambert-Eaton syndrome — also called Lambert-Eaton myasthenic syndrome (LEMS) — is a rare neuromuscular junction disorder. LEMS is most common in people with small cell lung cancer but may also occur in people with autoimmune disorders. In addition to limb weakness, symptoms may include eyelid drooping and difficulty speaking and swallowing.

Blood tests, EMG, and lung imaging may be used to diagnose Lambert-Eaton syndrome.

12. Guillain-Barré Syndrome

In Guillain-Barré syndrome, the immune system attacks and damages nerve cells. Like multiple sclerosis, this autoimmune disease affects myelin. A key feature of GBS is weakness or paralysis that usually starts in the legs and gets worse over hours or days. GBS may also cause double vision and trouble moving facial muscles.

Although GBS can occur at any age, it’s most common in people over 50. Diagnosis may include a spinal tap, an EMG, or an electrocardiogram (to check heart function).

Communicate With Your Doctor

Many conditions can look like myasthenia gravis, so it’s important to tell your healthcare provider about all your symptoms, including details such as when they started and how severe they are. To make sure you get the right diagnosis, your doctor may order several tests. This can take time, so try to be patient and work closely with your healthcare team throughout the process.

Find Your Team

On MGteam, the social network for people with myasthenia gravis and their loved ones, more than 2,800 members come together to ask questions, give advice, and share their stories with others who understand life with myasthenia gravis.

Were you initially diagnosed with another condition before MG? How long did it take to get the correct diagnosis? Share your experience in the comments below, or start a conversation by posting on your Activities page.