A fatal hyperthermic syndrome occurred in a patient with myokymia. The pati
ent suffered acute circulatory collapse and severe rhabdomyolysis associate
d with hyperthermia. Although these symptoms were similar to neuroleptic ma
lignant syndrome or malignant hyperthermia, he did not have a history of an
tipsychotic medication or anesthesia. Continuous muscular contraction due t
o myokymia likely led to the development of hyperthermic syndrome.