Queston #6637Note

Neuromyotonia (also called Isaac syndrome) is an autoimmune or paraneoplastic condition against voltage-gated potassium channels which leads to hyperexcitability and continuous firing of muscle fibers. EMG will show characteristic myokymic discharges. Symptoms can improve with phenytoin, carbamazepine, or topiramate.

Myotonia congenita occurs due to mutations of the chloride channels.

Paramyotonia congenita and hyperkalemic periodic paralysis occur secondary to mutations of a sodium channel gene (SCN4A).

The CACNA1S calcium channel gene is related to hypokalemic periodic paralysis.