Isaacs’ syndrome is a disorder that affects the peripheral nervous system. It’s sometimes classified as an autoimmune disorder, but not always.

Other names for Isaacs’ syndrome include:

  • neuromyotonia
  • acquired neuromyotonia
  • acquired autoimmune neuromyotonia
  • Isaacs-Merten syndrome
  • continuous muscle fiber activity syndrome
  • quantal squander syndrome
  • idiopathic generalized myokymia

Some of these terms are used inconsistently to refer to related but distinct disorders, so in this article we’ll use the more specific “Isaacs’ syndrome.”

This is an extremely rare condition, affecting fewer than 1,000 people in the United States.

Isaacs’ syndrome is rarely fatal, and several treatments are available to help manage it.

Read on to learn more about the causes, symptoms, and treatments for Isaacs’ syndrome.

The exact causes of Isaacs’ syndrome aren’t known, but it’s often broken down into two categories: acquired and hereditary.


The acquired form of Isaacs’ syndrome isn’t hereditary — that is, you don’t inherit it from your biological parents. Instead, it develops in response to a trigger or series of triggers.

The exact causes of acquired Isaacs’ syndrome are unknown, but it’s often associated with an autoimmune component. It’s also believed to be related to some types of cancer.


Sometimes genes or chromosomes can undergo changes, called mutations. These can be passed from biological parents to children during the reproductive process.

Some mutations produce no noticeable changes. Others are responsible for changes that are harmless, such as red hair or blue eyes.

Some mutations, though, can have harmful consequences that result in disease. Isaacs’ syndrome is one such condition that can be inherited.

Common symptoms of Isaacs’ syndrome include:

If you have Isaacs’ syndrome, you may notice that your muscles contract, twitch, or spasm continuously, especially the muscles in your arms and legs. This is even the case while you’re sleeping or under general anesthesia.

You may also find that your muscles have a delayed relaxation response. For example, if you shut your eyes tightly for several seconds, they may not open right away when you relax them.

It’s also been reported that Isaacs’ syndrome can be associated with:

Other symptoms of Issacs’ syndrome that are less common could include:

It’s also possible for the muscles controlling your ability to speak, breath, and swallow to be affected, but this is less common.

It’s possible for anyone to have Isaacs’ syndrome.

Because it can be an inherited condition, you’re at greater risk of Isaacs’ syndrome if you have a parent or sibling who has it.

Issacs’ syndrome can occur at any age, including childhood. Typically, onset begins between the ages of 15 and 60. In most cases, symptoms begin before the age of 40.

Both men and women can have Isaacs’ syndrome, but it’s slightly more common in men.

Acquired Isaacs’ syndrome is associated with cancer, especially thymoma.

Isaacs’ syndrome is often associated with cancer, but the connection remains unclear.

Between 21% and 25% of people diagnosed with Isaacs’ syndrome have recently had a tumor. About 20% of people with Isaacs’ syndrome have a tumor in their thymus gland, called thymoma.

Isaacs’ syndrome has also been reported after radiation therapy, which is sometimes used to treat cancer.

More research is needed to determine exactly how cancer, radiation therapy, and Isaacs’ syndrome might be linked.

Because Isaacs’ syndrome is so rare, it can be difficult to diagnose. Most doctors don’t have a lot of experience with Isaacs’ syndrome, and the symptoms can be similar to many other conditions.

If a doctor suspects you have Isaacs’ syndrome, it’s common to order a needle electromyography. Small needles will be used to insert electrodes into your muscles. While you rest, the electrodes measure the electrical activity of your muscles. The results of this test can be used to diagnose Isaacs’ syndrome.

A blood test can also be used to diagnose Isaacs’ syndrome. Most people with this condition have antibodies that attack voltage-gated potassium channels (VGKCs).

VGKCs are partly responsible for how electrical impulses travel through your body, affecting things such as the contraction of muscles. If you have anti-VGKC indicators in your blood, it could be a sign of Isaacs’ syndrome.

There are a variety of different treatments for Isaacs’ syndrome. Medications are often used. Physical therapy and other medical procedures could be used as well.


The most commonly used medications for treating Isaacs’ syndrome are anticonvulsants. Phenytoin and carbamazepine are frequently cited as effective treatments for the symptoms of Isaacs’ syndrome.

Physical therapy

The symptoms of Isaacs’ syndrome can sometimes lead to further complications such as weak grip strength or gait and balance problems. Physical therapy may be useful in countering these effects or regaining these skills, though it hasn’t been extensively researched for this condition.

Medical treatments

Plasma exchange has been demonstrated to have beneficial short-term effects in treating the symptoms of Isaacs’ syndrome. This is specifically relevant for people with anti-VGKC antibodies. It’s not well understood if this is an effective long-term treatment.

People with Isaacs’ syndrome respond to the treatments differently. This means that the outlook can vary greatly from one person to another.

There are several treatment plans available to try. For those who do respond well to treatment, it’s possible to see improvements within a few weeks. In some cases, the symptoms of Isaacs’ syndrome can be almost completely alleviated.

There’s no cure for Isaacs’ syndrome.

Isaacs’ syndrome can be progressive, meaning the symptoms become more severe over time. Isaacs’ syndrome is rarely fatal.

Isaacs’ syndrome is an extremely rare condition that causes continuous muscle twitching, spasming, and stiffening. There’s no cure, but it’s often treatable.

It can be inherited or acquired later in life, though the causes are still not well understood. A significant number of people with Isaacs’ syndrome are diagnosed with the disorder after having cancer, especially thymoma.

If you think you have symptoms similar to Isaacs’ syndrome, make an appointment with a doctor so you can share your concerns and investigate further.