Myotonia congenita

Alternative names:

Thomsen's disease

Definition:

An inheritable muscle disorder characterized by slow relaxation of the muscle.

Causes, incidence, and risk factors:

Myotonia congenita is inherited as an autosomal dominant or autosomal recessive disease. It is thought to involve the deficiency of a muscle enzyme known as true cholinesterase. The hallmark of myotonia congenita is myotonia, which is the inability of the muscle to relax quickly after voluntary relaxation has been initiated. For example, an affected person shaking hands with someone may open and disengage his or her hand very slowly.

Early symptoms may include gagging and difficulty in swallowing because oropharyngeal muscles are slow to relax. Initial movements may be stiff but improve with immediate repetition. Children with myotonia congenita often appear muscular and well developed.