Neuromyotonia (Isaacs syndrome)

Isaacs syndrome is a chronic neuromuscular condition that causes constant muscle contractions, even when you’re asleep or sedated. Also called neuromyotonia, this very rare disease has no known cause or cure.

In addition to neuromyotonia, Isaacs syndrome is also known as:

• Isaac’s syndrome
• Isaacs’ syndrome
• Isaacs-Mertens syndrome
• Continuous muscle fiber activity syndrome
• Quantal squander syndrome

Isaacs syndrome symptoms

Progressive muscle stiffness and constantly contracting or twitching muscles (myokymia) are the main symptoms of Isaacs syndrome. The movements of the muscles are sometimes described as a feeling of rippling muscles under the skin.

When you have Isaacs syndrome, muscle twitching is combined with delayed muscle relaxation. For example, when a person with Isaacs syndrome closes their jaw to chew on food, there may be a delay before the jaw releases to allow another chewing motion. These abnormal muscle actions make many everyday activities difficult.

Other Isaacs syndrome symptoms are:

• Diminished reflexes
• Increased size of calf muscles
• Increased sweating
• Muscle cramping or spasms
• Rapid heartbeat (bradycardia)
• Weight loss

Breathing and speech may be affected for some people. Most symptoms of Isaacs syndrome start between ages 15-60, but they can happen at any age.

Causes of Isaacs syndrome

The exact cause of Isaacs syndrome is unknown. Research shows that some cases are inherited from parents. Others happen without a family history.

In almost half the people who have Isaacs syndrome, specific antibodies attack a certain part of a peripheral nerve. When nerves are damaged, they send abnormal messages to muscles. Evidence points to the likelihood of there being other unidentified antibodies that contribute to symptoms of Isaacs syndrome.

People who have Isaacs syndrome sometimes also have conditions such as cancer, celiac disease, peripheral neuropathies, myasthenia gravis and thymomas (tumors of the thymus gland).

Diagnosis of Isaacs syndrome

Diagnosis of neuromyotonia depends on careful evaluation of your potential symptoms of Isaacs syndrome and results of electromyography (EMG) testing. Since the symptoms of Isaacs syndrome overlap with other neuromuscular disorders such as ALS, those other conditions need to be ruled out for an accurate diagnosis.

Treatments for Isaacs syndrome

Medications that stop convulsions (involuntary muscle contractions) are the main treatment for Isaacs syndrome. Medications such as oral corticosteroids may also be recommended.

If you have a tumor of the thymus gland (thymoma), you may have surgery to remove the tumor.

Isaacs syndrome treatments with blood products

Treatment with blood products is sometimes recommended for short-term relief of Isaacs syndrome symptoms.

• Blood plasma exchange: Apheresis machine is used to filter the plasma from the person’s blood and replace it with donated plasma.
• Intravenous immune globulin (IVIG) infusion: Immunoglobulins (antibodies) are separated from donated plasma from thousands of people and injected into the bloodstream of the person who has neuromyotonia.

Both neuromyotonia treatments with blood products take several hours to complete and are usually provided as outpatient procedures.

Clinical trials & Isaacs syndrome

Researchers are searching for better treatments for Isaacs syndrome. If you’re interested in participating in clinical trials, be sure to mention it to your health care team.