Myotonia congenita is an inherited condition that affects muscle relaxation. It is congenital, meaning that it is present from birth.
Thomsen's disease; Becker's disease
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.
The hallmark of this condition is myotonia -- 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:
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 look muscular and well-developed. They may not have symptoms of myotonia congenita until age 2 or 3.
Exams and Tests
The doctor may ask if there is a family history of myotonia congenita.
Kerchner GA, Lenz RA, Ptacek LJ. Channelopathies: Episodic and electrical disorders of the nervous system. In: Bradley WG, Daroff RB, Fenichel GM, Jankovic J, eds. Neurology in Clinical Practice. 5th ed. Philadelphia, PA: Butterworth-Heinemann: 2008:chap 68.
Joseph V. Campellone, M.D., Division of Neurology, Cooper University Hospital, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.