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 myasthenia gravis and congenital myasthenic syndrome have in common and how these conditions differ.

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Similarities Between Myasthenia Gravis and Congenital Myasthenic Syndrome

Myasthenia gravis and congenital myasthenic syndrome are chronic (long-term) conditions that require lifelong management.

Similar Symptom: Muscle Weakness

Both myasthenia gravis and congenital myasthenic syndrome cause fatigable weakness, meaning muscles get weaker the more they’re used. This weakness can affect the face, arms, 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 myasthenia gravis and congenital myasthenic syndrome affect muscles involved in breathing.

Similar Tests To Diagnose Myasthenia Gravis and Congenital Myasthenic Syndrome

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 myasthenia gravis-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 congenital myasthenic syndrome.

Differences in Symptoms of Myasthenia Gravis and Congenital Myasthenic Syndrome

Not all symptoms are similar between myasthenia gravis and congenital myasthenic syndrome.

In myasthenia gravis, severe muscle weakness can lead to a life-threatening complication called myasthenic crisis, which requires immediate medical care.

Congenital myasthenic syndrome can also cause other symptoms not usually seen in myasthenia gravis, including skeletal deformities, seizures, hearing loss, and kidney problems.

Differences in Causes of Myasthenia Gravis and Congenital Myasthenic Syndrome

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

In contrast, congenital (present at birth) myasthenic syndrome is almost always an inherited genetic condition that affects the neuromuscular junction. Researchers recently discovered some disease-causing variants can occur de novo, meaning they appear for the first time in the affected person. Inherited congenital myasthenic syndrome is 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.

Differences in Treatments for Myasthenia Gravis and Congenital Myasthenic Syndrome

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

Treatments for Myasthenia Gravis

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 myasthenia gravis may include:

• Medications such as pyridostigmine (Mestinon) to improve nerve-muscle communication
• Immunosuppressive drugs
• Complement inhibitors
• Intravenous immunoglobulin (IVIG) and plasma exchange to help regulate the immune response during myasthenia gravis zcrises
• Thymectomy (surgical removal of the thymus gland), which may help some people with myasthenia gravis
• Neonatal Fc receptor blockers

Which therapy your doctor recommends will depend on factors including which symptoms you have and how severe they are, what type of antibodies you test positive for, and your overall health.

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

Treatments for Congenital Myasthenic Syndrome

While pyridostigmine is used to treat certain subtypes of congenital myasthenic syndrome, it can worsen symptoms in other forms.

Congenital myasthenic syndrome treatment is based on the specific genetic mutation or subtype involved. Medications prescribed to treat CMS include:

• Acetylcholinesterase inhibitors, such as pyridostigmine (often used as first-line treatment)
• Carbonic anhydrase inhibitors
• Beta-2 adrenergic agonists
• Potassium channel blockers, such as amifampridine
• AChR open-channel blockers

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.

Differences in Who’s Affected by Myasthenia Gravis and Congenital Myasthenic Syndrome

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

The age of onset for myasthenia gravis in women is most often under 40 and in men most commonly over 60, according to the National Institute of Neurological Disorders and Stroke. However, myasthenia gravis can also develop in children.

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

Differences in Outlook for Myasthenia Gravis and Congenital Myasthenic Syndrome

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.

Symptoms can reappear after periods of remission. Permanent remission is uncommon, and most people who have myasthenia gravis 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 myasthenia gravis or congenital myasthenic syndrome 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.