Isaacs' syndrome

Alternate names

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

Definition

Isaacs' syndrome is a rare neuromuscular disorder that is characterized by progressive muscle stiffness; continuously contracting or twitching muscles (myokymia); and diminished reflexes.

Cause

• 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.

Signs and symptoms

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.

Clinical presentation

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

30%-79% of people have these symptoms

• Calf muscle hypertrophy(Increased size of calf muscles)
• EEG abnormality
• EMG: myokymic discharges
• Fasciculations(Muscle twitch)
• Hyperhidrosis(Excessive sweating)
• Muscle fibrillation
• Muscle spasm
• Muscle stiffness
• Weight loss

5%-29% of people have these symptoms

• Distal sensory impairment(Decreased sensation in extremities)

1%-4% of people have these symptoms

• Muscle weakness(Muscular weakness)

Diagnosis

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.

Treatment

• 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.

Prognosis

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.

NIH genetic and rare disease info

• NIH info on Isaacs' syndrome

Isaacs' syndrome is a rare disease.

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