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About isaacs-merten syndrome

What is isaacs-merten syndrome?

Acquired neuromyotonia is an inflammatory disorder characterized by abnormal nerve impulses from the peripheral nerves that result in continuous muscle fiber activity. Affected individuals often experience progressive muscle stiffness and cramping especially in the hands and feet, increased sweating, and delayed muscle relaxation. Symptoms may persist even during sleep or under general anesthesia.

What are the symptoms for isaacs-merten syndrome?

Acquired neuromyotonia is characterized by involuntary continuous muscle fiber activity (fasciculations, doublet and triplet discharges on electromyography) that cause stiffness and delayed relaxation in the affected muscles. Muscle twitching with a rippling appearance (myokymia) may occur along with these symptoms. Affected individuals may, at times, be unable to coordinate voluntary muscle movement and find difficulty in walking (ataxia). Other symptoms may include staggering and reeling (titubation), stiffness, and lack of balance in response to being startled. There may be diminished spontaneous gross motor activity.

The disorder is characterized by progressive stiffness, cramping, and weakness. Muscle activity is constant, and patients describe the feeling of continuous writhing or rippling of muscles under the skin. These movements continue during sleep. Diminished reflexes are also frequently a sign of this disorder. In some instances, muscle relaxation following voluntary muscle movement is delayed (grip myotonia) in the affected muscles. For example, affected individuals may not be able to open their fists or eyes immediately after closing them tightly for a few seconds.

Affected individuals frequently have excessive Sweating (hyperhidrosis), rapid heartbeats (tachycardia) and weight loss. Symptoms of Pain are common.

In slightly fewer than 20% of patients, a set of symptoms, including arrhythmias, excessive salivation, memory loss, confusion, hallucinations, constipation, personality change and sleep disorders, are found. In such cases the disorder may be referred to as Morvan syndrome.

Approximately 20% of affected individuals have a tumor of the thymus gland (thymoma). The thymus glands are the source of a number of specialized cells associated with autoimmune functions. The disorder is also associated with peripheral neuropathies and autoimmune diseases including myasthenia gravis in some individuals. It has also been reported following infections and radiation therapy.

What are the causes for isaacs-merten syndrome?

Acquired neuromyotonia is an autoimmune disease in which the immune system malfunctions so that it damages parts of one’s own body. Approximately 40% of affected individuals have antibodies to voltage-gated potassium channels (VGKC’s) that affect the points at which the signals from the nerve fiber meet the muscle cell (neuromuscular junction).

What are the treatments for isaacs-merten syndrome?

Acquired neuromyotonia may be treated with anticonvulsant drugs such as phenytoin or carbamazepine, which may stop the abnormal impulses and prevent the symptoms from reoccurring. 

Testing for acetylcholine receptor antibodies should be done if thymoma is suspected. The thymus gland should be surgically removed if thymoma is present.

What are the risk factors for isaacs-merten syndrome?

Aquired neuromyotonia is a rare disorder affecting males and females but is slightly more common among men. Disease onset is usually between the ages of 15 and 60 years but has also been reported in childhood.

Is there a cure/medications for isaacs-merten syndrome?

Plasma exchange (plasmapheresis) and intravenous immune globulin have been effective in a few cases but no long-term, controlled, clinical studies have been carried out.

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