Find information on medical topics, symptoms, drugs, procedures, news and more, written for the health care professional.

* This is a professional Version *

Isaacs Syndrome

by Michael Rubin, MDCM

Isaac syndrome causes neuromuscular manifestations, including myokymia.

Isaacs syndrome (neuromyotonia) is generally thought to be a channelopathy and sometimes occurs as a paraneoplastic syndrome. It may also occur in other disorders (eg, myasthenia gravis, thymoma, cancer, amyloidosis) or can be inherited. Cause is unknown. Abnormalities are thought to originate in a peripheral nerve because they are abolished by curare but usually persist after general anesthesia.

The limbs are most affected. The sine qua non is myokymia—continuous muscle twitching described as bag-of-worms movements. Other symptoms include carpopedal spasms, intermittent cramps, increased sweating, and pseudomyotonia (impaired relaxation after a strong muscle contraction but without the typical waxing-and-waning EMG abnormality of true myotonia).

Carbamazepine or phenytoin may relieve these symptoms. Plasma exchange and IVIG are usually beneficial.

Drugs Mentioned In This Article

  • Drug Name
    Select Trade
  • DILANTIN
  • TEGRETOL

* This is a professional Version *