Isaacs’ Syndrome

Isaacs’ syndrome, also called neuromyotonia, is a rare neuromuscular disorder. The condition makes your nerves fire too much, which overstimulates your reflexes and muscles. It causes muscle stiffness, muscle cramps, slow reflexes and excessive sweating. Symptoms get progressively worse over time and can affect daily activities.


What is Isaacs’ syndrome?

Isaacs’ syndrome is a rare neuromuscular disorder. The condition causes nerves within your peripheral nervous system to be overly excited, leading to involuntary muscle firing. People with the condition experience stiffness, cramps and twitching in their muscles. It can also affect your autonomic nervous system, leading to changes in sweating and heart rate.

It’s also called:

  • Continuous muscle fiber activity syndrome.
  • Isaacs-Mertens syndrome.
  • Neuromyotonia.
  • Quantal squander syndrome.


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How common is Isaacs’ syndrome?

Isaacs’ syndrome is extremely rare. Scientists aren’t sure how many people have it, but only a couple hundred cases have been reported.

Symptoms of muscle cramps and muscle twitching (fasciculations) are extremely common in adults and aren’t usually serious. For the vast majority of people, these symptoms don’t indicate a more serious neurologic condition like Isaacs’ syndrome.

Who might get Isaacs’ syndrome?

The signs of Isaacs’ syndrome usually begin between the ages of 15 and 60. But it has been reported in younger people and even infants.

The disorder may be associated with other conditions, including:


Symptoms and Causes

What causes neuromyotonia?

Neuromyotonia can be:

  • Acquired: This type of Isaacs’ syndrome is an autoimmune condition. An autoimmune condition happens when your immune system attacks normal cells as if they were foreign organisms. Specifically, in Isaacs’ syndrome, about 50% of people have antibodies that target channels that control movement of the electrolyte potassium into and out of your nerve. The movement of potassium in and out of your nerve affects nerve firing.
  • Hereditary: This type of Isaacs’ syndrome is genetic. It’s passed down from one generation to another (inherited).

What are the symptoms of Isaacs’ syndrome?

The signs and symptoms of Isaacs’ syndrome generally happen throughout the day, even during sleep. Muscle symptoms are most common in your arms and legs, but they can affect other muscles in your body.

Symptoms include:

  • Ataxia, trouble coordinating movement.
  • Delayed muscle relaxation.
  • Excessive sweating (hyperhidrosis).
  • Changes in heart rate.
  • Fatigue and insomnia.
  • Muscle cramping, spasms, stiffness and weakness that progressively worsen.
  • Myokymia, which is twitching, quivering or rippling of the muscles. This is sometimes described as looking or feeling like worms under your skin.
  • Trouble speaking or breathing if the muscles of your throat are affected.


Diagnosis and Tests

How is Isaacs’ syndrome diagnosed?

Your healthcare provider may order tests to confirm Isaacs’ syndrome or rule out other disorders. Tests may include:

  • Blood tests to identify certain antibodies present in up to half of people with Isaacs’ syndrome.
  • Nerve conduction studies and electromyograms, which measure how your muscles and nerves work.
  • Imaging studies such as a CT scan or MRI.

Sometimes, Isaacs’ syndrome is misdiagnosed as another disorder, such as stiff-person syndrome, rippling muscle syndrome or cramp-fasciculation syndrome.

Management and Treatment

How is Isaacs’ syndrome treated?

There’s no cure for Isaacs’ syndrome. Treatment aims to address your symptoms and maximize daily function. If Isaacs’ syndrome is associated with another autoimmune disease or a malignancy, then treatment of these other conditions is important well. For Isaacs’ syndrome, your healthcare provider might recommend:

  • Anticonvulsant (antiseizure) medications such as phenytoin and carbamazepine to relieve muscle stiffness, spasms and pain.
  • Immunosuppressive medications such as azathioprine and methotrexate.
  • Intravenous immunoglobulin, a solution containing antibodies from donors.
  • Oral corticosteroids such as prednisolone.
  • Plasma exchange to filter toxins and unhealthy antibodies out of your blood (in individuals who have abnormal antibodies).


How can I prevent Isaacs’ syndrome?

Because scientists don’t understand what causes Isaacs’ syndrome, there currently aren’t any strategies to prevent it.

Outlook / Prognosis

What is the outlook for people with neuromyotonia?

The outlook for someone with Isaacs’ syndrome varies. It depends on the severity of the disorder, the underlying cause, treatment effectiveness and any associated medical conditions.

Neuromyotonia symptoms progressively worsen over time. They can significantly limit movement and interfere with daily activities.

Although there’s currently no cure, the condition isn’t generally fatal.

Living With

How can I best learn to cope with Isaacs’ syndrome?

Some people with Isaacs’ syndrome have found success managing the physical and psychological effects of Isaacs’ syndrome by:

  • Advocating for people with neuromuscular disorders.
  • Attending counseling sessions to learn coping strategies.
  • Connecting with other people with the condition, particularly over social media.
  • Meditating.
  • Practicing yoga.
  • Walking.

What else can I ask my doctor about Isaacs’ syndrome?

If you’re diagnosed with neuromyotonia, consider asking your doctor the following questions:

  • What caused Isaacs’ syndrome in my case?
  • Do I have any of the associated medical conditions?
  • How do we know this is Isaacs’ syndrome and not ALS or another neuromuscular condition?
  • What areas of my body will be affected?
  • What treatments do you recommend? Am I eligible for any clinical trials?
  • Would physical or occupational therapy help me?
  • Can you refer me to a counselor or support group to help me cope?
  • Should anyone else in my family be tested for Isaacs’ syndrome?

A note from Cleveland Clinic

Isaacs’ syndrome is a rare neuromuscular disorder that causes overactive nerves and muscles. If you’ve been diagnosed with the condition, talk to your healthcare provider. They can test you for related conditions and help you manage symptoms such as muscle twitching and stiffness.

Medically Reviewed

Last reviewed on 04/01/2022.

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