Ten Years' Follow-Up of a Family With Myokymia and Muscle Cramps Without Ataxia.

We report 10 years' follow-up of the previously described family with a novel mutation of the KCNA1 gene. The family consisted of 3 affected boys (first seen at ages 3, 11, and 12) and their affected mother and asymptomatic father and sister. They clinically presented with diffuse myokymia, muscle cramps, and lower limb spasticity without ataxia, but episodic ataxia developed later during adolescence and early adulthood. Long-term follow-ups of families with known KCNA1 gene mutation are rarely mentioned in the literature. Treatment with carbamazepine, 600 to 800 mg daily resulted in cessation of muscle cramps and marked improvement of lower leg symptoms. In the youngest child, after 2 years carbamazepine had to be changed to oxcarbazepine because of side effects. Carbamazepine and oxcarbazepine are both effective in treatment of symptoms related to KCNA1 gene mutation. Symptoms will reoccur if treatment is stopped and there is variability of symptom severity between family members.