Myotonia congenita

Myotonia congenita is an inherited condition that affects muscle relaxation. It is congenital, meaning that it is present from birth. It occurs more frequently in northern Scandinavia.

Causes

Myotonia congenita is caused by a genetic change (mutation). It is passed down from either one or both parents to their children (inherited).

Myotonia congenita is caused by a problem in the part of the muscle cells that are needed for muscles to relax. Abnormal repeated electrical signals occur in the muscles, causing a stiffness called myotonia.

Symptoms

The hallmark of this condition is myotonia. This means the muscles are unable to quickly relax after contracting. For example, after a handshake, the person is only very slowly able to open and pull away their hand.

Early symptoms may include:

• Difficulty swallowing
• Gagging
• Stiff movements that improve when they are repeated
• Shortness of breath or tightening of the chest at the beginning of exercise
• Frequent falls
• Difficulty opening eyes after forcing them closed or crying

Children with myotonia congenita often look muscular and well-developed. They may not have symptoms of myotonia congenita until age 2 or 3.

Exams and Tests

The health care provider may ask if there is a family history of myotonia congenita.

Tests include:

• Electromyography (EMG, a test of the electrical activity of the muscles) and nerve conduction studies (NCS)

  Electromyography

  Electromyography (EMG) is a test that checks the health of the muscles and the nerves that control the muscles.

  

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• Genetic testing
• Muscle biopsy

  Muscle biopsy

  A muscle biopsy is the removal of a small piece of muscle tissue for examination.

  

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Treatment

Mexiletine is a medicine that treats symptoms of myotonia congenita. Other treatments include:

• Phenytoin
• Procainamide
• Quinine (rarely used now, due to side effects)
• Tocainide
• Carbamazepine

Support Groups

The following resources can provide more information on myotonia congenita:

• Muscular Dystrophy Association -- www.mda.org/disease/myotonia-congenita
• National Library of Medicine, Medline Plus -- medlineplus.gov/genetics/condition/myotonia-congenita/

Outlook (Prognosis)

People with this condition can do well. Symptoms only occur when a movement is first started. After a few repetitions, the muscle relaxes and the movement becomes normal.

Some people experience the opposite effect (paradoxical myotonia) and get worse with movement. Their symptoms may improve later in life.

Possible Complications

Complications may include:

• Aspiration pneumonia caused by swallowing difficulties

  Aspiration pneumonia

  Pneumonia is inflammation (swelling) and infection of the lungs or large airways. Aspiration pneumonia occurs when food or liquid is breathed into th...

  

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• Frequent choking, gagging, or trouble swallowing in an infant
• Long-term (chronic) joint problems
• Weakness of the abdominal muscles

When to Contact a Medical Professional

Contact your provider if your child has symptoms of myotonia congenita.

Prevention

Couples who want to have children and who have a family history of myotonia congenita should consider genetic counseling.

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