Myasthenia gravis (MG) and congenital myasthenic syndrome (CMS) have similar names and some overlapping symptoms. Doctors even use some of the same tests to diagnose them. However, these conditions have key differences, including how they’re treated, so getting the right diagnosis is essential.

Read on to learn more about what MG and CMS have in common and how these conditions differ.

Similarities Between Myasthenia Gravis and Congenital Myasthenic Syndrome

Myasthenia gravis and congenital myasthenic syndrome are chronic (long-term) conditions that require lifelong management. Although they are separate conditions, their symptoms are often similar.

Main Symptom: Muscle Weakness

Both myasthenia gravis and congenital myasthenic syndrome cause fatigable weakness, meaning muscles get weaker the more they’re used but may improve with rest. This weakness can affect the face, arms, and legs and the breathing muscles.

When facial muscles are involved, symptoms may include:

• Double vision
• Ptosis (droopy eyelids)
• Difficulty speaking
• Trouble holding up your head
• Problems with swallowing

Shortness of breath can occur in both conditions because both MG and CMS affect muscles involved in breathing. However, in MG, severe weakness of these muscles can lead to a life-threatening complication called myasthenic crisis, which requires immediate medical care. CMS can also cause other symptoms not usually seen in MG, including skeletal deformities, seizures, hearing loss, and kidney problems.

Tests To Diagnose MG and CMS

To diagnose myasthenia gravis or congenital myasthenic syndrome, your neurology team will perform a series of tests, which may include:

• A physical and neurological evaluation to check muscle strength and reflexes
• Blood tests to look for MG-related antibodies (proteins), which aren’t present in CMS
• Nerve conduction tests, such as repetitive nerve stimulation and electromyography, to measure how well nerves and muscles are working
• Genetic testing to identify inherited types of CMS, which are caused by specific gene mutations (changes) passed down in families

A muscle biopsy (removing a small piece of muscle tissue for lab testing) may also be done to diagnose CMS.

Your doctor will walk you through what to expect for each test performed and help you understand the results.

Differences Between Myasthenia Gravis and Congenital Myasthenic Syndrome

Despite sharing some symptoms and diagnostic tests, MG and CMS are distinct conditions with different causes and treatment options.

Causes of MG vs. CMS

Myasthenia gravis is an autoimmune disease. In MG, the immune system produces abnormal proteins called autoantibodies that attack the neuromuscular junction — the place where nerves send signals to muscles. MG isn’t inherited or contagious, although occasionally more than one family member has it.

Congenital myasthenic syndrome is a genetic condition caused by inherited gene mutations. Most types of CMS follow an autosomal recessive pattern, which means both parents must carry the gene for their child to develop the condition. However, slow-channel CMS is autosomal dominant, meaning just one parent needs to pass on the mutation for the child to inherit the condition.

People Affected by MG vs. CMS

Either condition can occur at any age, but certain age groups are more commonly affected.

Myasthenia gravis most often develops in women under 40 and men over 60, according to the National Institute of Neurological Disorders and Stroke. However, MG can also develop in children.

Since congenital myasthenic syndrome is a hereditary condition, symptoms are usually present at or near birth or in early childhood. CMS can cause delays in certain milestones, such as crawling or walking. Generally, the earlier symptoms appear, the more severe the condition tends to be.

Treatments for MG vs. CMS

Because myasthenia gravis and congenital myasthenic syndrome have different causes, their treatments also differ.

Since myasthenia gravis is an autoimmune disease, treatments focus on regulating the immune system to help prevent attacks on the neuromuscular junction. Treatment options for MG may include:

• Medications such as pyridostigmine (Mestinon) to improve nerve-muscle communication
• Immunosuppressive drugs to reduce immune system activity
• Plasma exchange, a procedure that removes harmful antibodies from the blood
• Intravenous immunoglobulin (IVIG) to regulate the immune response
• Thymectomy (surgical removal of the thymus gland), which may help some people with MG

Doctors may also recommend lifestyle changes such as getting more rest, improving nutrition, and exercising regularly. Because stress can trigger MG flare-ups (worsening of symptoms), finding ways to manage stress is important.

Treatment of CMS is based on the specific genetic mutation involved. Medications prescribed to treat CMS include:

• Acetazolamide
• Albuterol
• Ephedrine
• Fluoxetine

Doctors may also recommend occupational or physical therapy, speech therapy, and breathing or feeding support. Some people may need surgery to correct deformities in the spine or feet.

Outlook for MG vs. CMS

Myasthenia gravis flare-ups can be triggered by factors such as infection, stress, or surgery. Remissions — periods when symptoms get better or disappear — can also occur. However, permanent remission is rare, and most people who have MG experience some symptoms even during remission.

Congenital myasthenic syndrome tends to be more stable, with fewer fluctuations in symptoms. However, severity varies from person to person. Some people with CMS experience only mild weakness, while others have severe muscle weakness that may limit movement.

With the right medical treatment and support, many people with MG or CMS can effectively manage their symptoms. Working closely with a healthcare team is key to getting the correct diagnosis and finding the treatment plan that works best for you.

Talk With Others Who Understand

On MGTeam, the social network for people with myasthenia gravis and their loved ones, more than 2,000 members come together to ask questions, give advice, and share their stories with others who understand life with myasthenia gravis.

Have you been diagnosed with MG or congenital myasthenic syndrome? Did your doctor need to rule out other conditions before you received a diagnosis? Share your experience in the comments below, or start a conversation by posting on your Activities page.