Myotonic lid lag in hypokalaemic periodic paralysis

Intermittent failure of muscle excitation and con-tractility occurs in the periodic paralyses. Affected individuals present clinically with recurrent episodes of skeletal muscle weakness, often with a family history of such attacks. Alteration in serum potas-sium during attacks has led to the designation of three types of periodic paralysis, namely, hypoka-laemic, normokalaemic, and hyperkalaemic. The hyperkalaemic form is referred to as adynamia episodica hereditaria by Gamstorp in her description of such patients (Gamstorp, 1956). The response to administered potassium differs in the various forms of periodic paralysis: in the hypokalaemic type, exo-genous potassium reverses the acute attack and is also prophylactic (Aitken, Allott, Castleden, and Walker, 1937); conversely, patients with the normo-kalaemic and hyperkalaemic types are potassium intolerant, i.e., administration of even modest doses of potassium precipitates an attack or aggravates one that has begun spontaneously (Gamstorp, 1956;