Myotonia Congenita


Myotonia congenita

Description, Causes and Risk Factors:

ICD-10: G71.12

Alternative Name: Thomsen disease, Becker's generalized myotonia, Paramyotonia congenita, Schwartz Jampel syndrome.

Abbreviation: MC.

Myotonia congenita is a condition caused by a mutation in the chloride ion channel of the skeletal muscle. While the degree of severity can vary widely from person to person, the most common and obvious symptom is the inability to relax muscles after they are contracted, especially after being in a static position such as sitting, lying or standing still. This looks like stiffness to an observer and is the same condition that you may have seen in “fainting goats.”

Myotonic disorders are usually caused by errors in the gene that helps to determine the structure of the body's skeletal muscle cells. In muscle cells, there are structures known as ion channels that allow the muscle to contract and then to relax after a contraction. When a muscle is affected by a myotonic disorder, these ion channels do not function properly. This dysfunction affects the ability of a muscle to relax after it has contracted. Until relaxation can properly occur, the muscles remain stiff and unusable, causing myotonic stiffness.

Research says that CLCN1, the gene encoding the major skeletal muscle chloride channel, is localized to chromosome 7q35 locus. A mutation in this gene can cause either dominant Thomsen or recessive Becker type of myotonia.

Positive family history, early appearance and lack of progression of myotonia and presence of generalized muscular hypertrophy distinguish myotonia congenita from myotonic dystrophy.

Other factors which may influence the stiffness include sudden loud noises, intense exercise, stress, cold weather, exposure to pesticides and herbicides, and certain foods or medications.

The muscles affected by myotonia congenita include hands, arms, legs, abs, back, diaphragm, neck, face, throat (upper part of esophagus), eyes and even tongue. When the tongue is stiff it can impair speech and the student may sound drunk. This stiffness may last for many seconds, for instance when rising up out of a chair or desk or grasping a doorknob. Usually the muscles begin to relax and work more freely after they are flexed and warmed up. However a sustained pause in activity or movement tends to “reset” the whole cycle and the warming up must take place again.

Unlike muscular dystrophy it does not become progressively worse over time and a person with MC will have a normal lifespan, but the amount of stiffness and resulting pain and cramping can vary from one day to the next and even one hour to the next. A child may come to school and seem perfectly normal, but after being exposed to cold at recess the stiffness may become so severe he or she could have trouble swallowing food at lunch. While the physical manifestations of this condition are not usually that severe, the emotional impact can be devastating if children are subjected to constant teasing, bullying and condescending comments from staff. MC does not affect mental function and it can further add to humiliation and embarrassment if children are put in to special education classes. A child with MC is just as likely to have a learning disability from other causes as the rest of the population so screenings are appropriate, but any deficits are not caused by MC and should be investigated further with the parents and family physician.

Symptoms:

The hallmark of this condition is the myotonia -- the inability of the muscle to quickly relax after contracting. For example, after a handshake, the person is only very slowly able to open and pull away his hand.

Early symptoms may include:

    Difficulty in swallowing.

  • Gagging.

  • Stiff movements that improve when they are repeated.

  • Shortness of breath or tightening of the chest at the beginning of exercise.

Children with myotonia congenita often appear to be muscular and well-developed. The child may not have symptoms of myotonia congenita until age 2 or 3.

Diagnosis:

A doctor, outside of the laboratory, can do many of the diagnostic tests formyotonic disorders. One way is testing for myotonic reactions tostrenuous movement, cold temperatures, percussion, or other stimuli. It isimportant, however, that these disorders are differentiated from other,more severe progressive disorders like myotonic dystrophy. To do this,doctors will often need a number of laboratory tests that will give moreconcrete results.

These will often include: an electromyogram (EMG) test to measure theelectrical activity in the muscle; a blood and DNA analysis to look for agenetic mutation; or even a muscle biopsy, which will not provide a finaldiagnosis of a myotonic disorder, but is a good way of testing for manytypes of progressive muscle problems.

Treatment:

There are no cures for any of the myotonic disorders, but most people learn to live comfortably with their symptoms without any kind of treatment. If myotonia becomes more severe, however, there are a number of drugs that have proved to be effective in relieving myotonic symptoms. The most widely used of these is mexiletine, but others such as quinine, procanimide, tegretol, and phenytoin have also been used with some success.

As with all drug treatments, the major drawback is always the side effects, which can be quite serious in themselves. Most people affected by myotonic stiffness usually find that experience is the best remedy. Once a person knows what types of situations will bring about myotonic attacks, then they will be more prepared and be better able to avoid them in the future.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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