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Myotonia congenita

Thomsen's disease; Becker's disease

 

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 his 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)
  • Genetic testing
  • Muscle biopsy

 

Treatment

 

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

  • Phenytoin
  • Procainamide
  • Quinine
  • Tocainide
  • Carbamazepine

 

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
  • 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

 

Call 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.

 

 

References

Kerchner GA, Ptácek LJ. Channelopathies: Episodic and electrical disorders of the nervous system. In: Daroff RB, Jankovic J, Mazziotta JC, Pomeroy SL, eds. Bradley's Neurology in Clinical Practice. 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 99.

Sarnat HB. Muscular dystrophies. In: Kliegman RM, Stanton BF, St Geme JW, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2016:chap 609.

Selcen D. Muscle diseases. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 421.

 
  • Superficial anterior muscles

    Superficial anterior muscles - illustration

    Superficial muscles are close to the surface of the skin. Muscles which lie closer to bone or internal organs are called deep muscles.

    Superficial anterior muscles

    illustration

    • Superficial anterior muscles

      Superficial anterior muscles - illustration

      Superficial muscles are close to the surface of the skin. Muscles which lie closer to bone or internal organs are called deep muscles.

      Superficial anterior muscles

      illustration


     

    Review Date: 2/27/2016

    Reviewed By: Amit M. Shelat, DO, FACP, Attending Neurologist and Assistant Professor of Clinical Neurology, SUNY Stony Brook, School of Medicine, Stony Brook, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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