Causes, Symptoms, Treatment and More


Isaac’s syndrome is a rare condition that causes uncontrollable muscle activity. The muscle movement takes place continuously, even during sleep or while a person is under anesthesia.

Other names for Isaac’s syndrome, or IS, include:

  • neuromyotonia
  • continuous muscle fiber activity syndrome
  • Isaacs-Mertens syndrome

IS is an autoimmune disease, which causes the body’s immune system to attack its own tissues. The symptoms of IS are lifelong, but they are manageable with treatment.

This article discusses the symptoms, causes, and treatments of IS.

A man with Isaac's syndrome is sleeping.Share on Pinterest
In people with IS, which is more common in men, uncontrollable muscle activity continues during sleep.

IS is a rare autoimmune disease. It occurs when the immune system, which is essential to protect the body from infection, mistakenly attacks healthy tissues and organs. There are currently 100-200 reported cases of IS worldwide.

IS causes peripheral nerves to become hyperactive and burn continuously. This causes uncontrollable nerve and muscle activity, which causes various symptoms. For example, it can lead to muscle spasms or stiffness.

IS can develop in anyone at any age, but it is more more common in men than in women.

The syndrome usually develops between 15-60 age. Most people will experience symptoms before the age of 10 40 years.

The symptoms and severity of IS vary. Most symptoms are related to uncontrollable nerve or muscle activity. The symptoms usually occur continuously, even during sleep.

Common symptoms of IS include:

  • continuous contraction or twitching
  • muscle stiffness and cramps that get worse over time
  • increased or excessive sweating
  • muscle strain
  • slowed reflexes
  • gradual muscle loss
  • difficulty coordinating movements and walking
  • weight loss
  • increased calf muscle size
  • increased heart rate

Around 20% of people with IS also have Morvan syndrome. The symptoms of Morvan syndrome include:

  • irregular heartbeat
  • amnesia, confusion and hallucinations
  • excessive salivation
  • constipation
  • personality changes
  • sleep problems

Doctors aren’t sure what causes the body to attack healthy tissue, as in people with IS. However, it appears to be related to genetics, among other health factors.

It is possible to inherit or acquire ISIS later in life. Acquired IS tends to develop with other conditions, such as:

Less often, IS can develop with:

Most treatment plans for IS focus on reducing symptoms, such as muscle stiffness and spasms.

Common treatments for managing IS symptoms include:

  • anticonvulsant medications, such as valproic acid, lamotrigine, and carbamazepine
  • plasma exchange
  • oral corticosteroids, such as prednisolone
  • non-steroidal drugs that suppress the immune system, such as methotrexate and azathioprine
  • acetazolamide

The exact treatment depends on the type and severity of the symptoms. There may also be additional treatments if IS develops with other conditions.

To diagnose IS, a doctor will check a person’s medical history and perform a physical exam. Doctors usually look for signs that include:

  • continuous muscle contractions or spasms
  • tics or shocks
  • muscle cramps

Muscle spasms can mainly affect the hands, feet or face.

If a doctor suspects someone has IS, they will use an electromyographic (EMG) test. The EMG test examines muscle and nerve activity.

The doctor may also need blood or urine tests to check for signs of the condition, such as specific antibodies. They can use a medical imaging scan, such as a MRI, to check for signs of muscle and nerve damage.

Because IS is a rare disease, it can be difficult to detect and some symptoms may resemble those of other conditions.

The doctor will want to rule out the presence of common conditions, as:

There is no cure currently for IS, but it is possible to manage symptoms with ongoing treatment. Each case of IS involves different symptoms of varying severity. IS is disabling but rarely life-threatening.

People who develop Morvan syndrome can develop severe symptoms that can be fatal. In many cases, the outlook will depend on other conditions that someone with IS can develop.

IS is a rare autoimmune disease that causes continuous and uncontrollable muscle and nerve activity. The syndrome can develop with other conditions, such as cancer or other autoimmune diseases.

It is unclear what exactly causes IS. There is no cure for the condition, but there are several treatments to manage the symptoms over the long term. For example, some drugs suppress the immune system and reduce symptoms.

Treating IS can also prevent further muscle and nerve damage. The outlook for IS may also depend on the presence of other conditions.

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