This is a rare hereditary disease characterised by prolonged tonic contraction and relaxation of the muscles both at the beginning and the end of voluntary movement. It has an autosomal dominant pattern of inheritance.
Neonates with this condition may present with an odd cry and difficulty feeding and opening his eyes.
Muscular development is good and hypertrophy may occur giving the child a Herculean look. Atrophy may not occur until late in the disease. Myotonia may be aggravated by cold and decreases with continued activity.
Sufferers may be unaware of the condition. There is improvement with increasing age. Patients with this condition have a normal IQ.
Treatment with quinidine and procainamide may be helpful.
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