Muscle cramps, muscle pain, percussive myotonia 
– think neuromyotonia/Isaac syndrome 

Neuromyotonia is an autoimmune or paraneoplastic condition against voltage-gated potassium channels which leads to hyperexcitiability and continuous firing of muscle fibers
– EMG will show characteristic myokymic dischargers 
– sx can improve with phenytoin, carbamazepine, and topiramate 

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Myotonia congenita occurs due to mutations of Cl channels 

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

CACNA1S calcium channel gene is related to hypokalmic periodic paralysis