What is the definition of Isaacs' Syndrome?

Isaacs' syndrome is a rare neuromuscular disorder that is characterized by progressive muscle stiffness; continuously contracting or twitching muscles (myokymia); and diminished reflexes. Signs and symptoms generally develop between ages 15 and 60, with most people experiencing symptoms before age 40. Although the exact underlying cause is unknown, there appear to be hereditary and acquired (non-inherited) forms of the condition. Treatment is based on the signs and symptoms present in each person.

What are the alternative names for Isaacs' Syndrome?

  • Neuromyotonia
  • Isaac's-Merten's syndrome
  • Continuous muscle fiber activity syndrome
  • Quantal squander syndrome
  • Acquired neuromyotonia
  • Isaac syndrome
  • Isaac-Mertens syndrome
  • Peripheral nerve hyperexcitability

What are the causes for Isaacs' Syndrome?

The exact cause of Isaacs' syndrome is poorly understood. There appear to be hereditary and acquired (non-inherited) forms of the condition. The acquired forms are often associated with malignancies, peripheral neuropathies, and a variety of autoimmune disorders of the nervous system.  

What are the symptoms for Isaacs' Syndrome?

The signs and symptoms of Isaacs' syndrome generally develop between ages 15 and 60, with most people showing symptoms before age 40. Although the symptoms can vary, affected people may experience:
  • Progressive stiffness, cramping and weakness
  • Muscle twitching with a rippling appearance (myokymia)
  • Delayed muscle relaxation
  • Diminished reflexes
  • Muscle atrophy
  • Ataxia (difficulty coordinating voluntary movements)
  • Increased sweating
These symptoms generally persist throughout the day, even during sleep or when under general anesthesia. Speech and breathing may also be affected if the muscles of the throat are involved. Smooth muscles and cardiac (heart) muscles typically are spared.

What are the current treatments for Isaacs' Syndrome?

The treatment of Isaacs' syndrome is based on the signs and symptoms present in each person. For example, anticonvulsant medications such as phenytoin and carbamazepine may be prescribed to relieve stiffness, muscle spasms, and pain. Plasma exchange may provide short-term relief for people with some forms of acquired Isaacs' syndrome. Plasma exchange is a method by which whole blood is removed from the body and processed so that the red and white blood cells are separated from the plasma (liquid portion of the blood). The blood cells are then returned to the patient without the plasma, which the body quickly replaces. If there is no response or poor response to plasma exchange, some studies suggest that intravenous infusions of immunoglobulins (IvIg therapy) may be beneficial.

What is the outlook (prognosis) for Isaacs' Syndrome?

The long-term outlook (prognosis) for people with Isaacs' syndrome varies and largely depends on the underlying cause. In general, there is no cure for the condition although it is generally not fatal.

How is Isaacs' Syndrome diagnosed?

A diagnosis of Isaacs' syndrome is often suspected based on the presence of characteristic signs and symptoms. Additional testing can then be ordered to confirm the diagnosis, evaluate for associated conditions (i.e. malignancies and autoimmune disorders) and rule out other disorders that may cause similar features. This testing may included:
  • Specialized laboratory studies on blood and/or urine
  • Imaging studies such as a CT scan or MRI scan
  • Electromyography which checks the health of the muscles and the nerves that control them.
  • Condition: Acquired neuromyotonia in children
  • Journal: Developmental medicine and child neurology
  • Treatment Used: Sodium channel blockers
  • Number of Patients: 3
  • Published —
The case discusses three children with acquired neuromyotonia.
  • Condition: Stiff-Person Syndrome due to Secondary Adrenal Insufficiency
  • Journal: Rinsho shinkeigaku = Clinical neurology
  • Treatment Used: Hydrocortisone (10?mg/day) and 75??g/day of Thyroid Hormone
  • Number of Patients: 1
  • Published —
This case report describes a 56-year-old woman diagnosed with panhypopituitarism treated with hydrocortisone (10?mg/day) and 75??g/day of thyroid hormone.

There are no recent clinical trials available for this condition. Please check back because new trials are being conducted frequently.