Myoclonus refers to quick, lightning-like jerks (contractions)
of a muscle or a group of muscles. Myoclonus may involve only
one hand, a group of muscles in the upper arm or leg, or a group
of facial muscles. Or it may involve many muscles at the same
time. Hiccups are a type of myoclonus that involves only the
diaphragm, the muscle that separates the chest from the abdomen.
Myoclonus may occur normally, often when a person is falling
asleep. Or it may result from a disorder, such as the following:
Myoclonus can occur after a person takes high doses of certain
drugs such as antihistamines, some antidepressants (such as
amitriptyline), bismuth, levodopa, or opioids (narcotics).
Myoclonus can be mild or severe. Muscles may jerk quickly or
slowly, rhythmically or not. Myoclonus may occur once in a while
or frequently. It may occur spontaneously or be triggered by a
stimulus, such as a sudden noise, light, or a movement. For
example, reaching for an object or taking step may trigger jerks
that disrupt the movemen