Myotonia congenita

Myotonia congenita
Other names	Congenital myotonia, Thomsen syndrome, Becker syndrome
Specialty	Neurology
Symptoms	Delayed relaxation of muscles, falls, difficulty swallowing
Usual onset	Childhood
Types	Autosomal dominant (Thomsen disease), autosomal recessive (Becker disease)
Causes	Genetic, CLCN1 mutations
Diagnostic method	Clinical, genetic testing
Differential diagnosis	Myotonic dystrophy, Paramyotonia congenita
Treatment	Physiotherapy, medication
Medication	quinine, phenytoin, carbamazepine, mexiletine
Frequency	1 in 10,000 (Finland) - 1 in 100,000 (worldwide)

Myotonia congenita is a congenital neuromuscular channelopathy that affects skeletal muscles (muscles used for movement). It is a genetic disorder. The hallmark of the disease is the failure of initiated contraction to terminate, often referred to as delayed relaxation of the muscles (myotonia) and rigidity.^[1] Symptoms include delayed relaxation of the muscles after voluntary contraction (myotonia), and may also include stiffness, hypertrophy (enlargement), transient weakness in some forms of the disorder (from certain genetic mutations), severe masseter spasm, and cramping. The condition is sometimes referred to as fainting goat syndrome, as it is responsible for the eponymous 'fainting' seen in fainting goats when presented with a sudden stimulus. Of note, myotonia congenita has no association with malignant hyperthermia (MH).