Myotonia congenita

  • Definition
    • 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.

  • Alternative Names
    • Thomsen's disease; Becker's disease

  • 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:

  • 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.