Myoclonic seizures (myo meaning muscle, clonic meaning jerk) is a sudden involuntary contraction of muscle groups. In Doose syndrome, myoclonic jerks consist of symmetric, mostly generalized jerks, accentuated in the arms and the shoulders and frequently simultaneously with a head nod; both the arms may fling out together and simultaneously a head nod may occur. Sometimes the entire body may jerk, just like a startle response. As is the case with all generalized seizures, the child is not conscious during the event but the seizure is so brief that the person appears to remain fully conscious. The intensity of these seizures is variable and ranges from violent myoclonic jerks with sudden falls to mild abortive forms presenting simply as short irregular twitches or head nods.
The jerk arises from deep structures in the brainstem that control posture and tone in the body. A sudden increase in tone in a muscle group will cause a sudden movement of that part of the body. An abrupt increase in tone in the flexor muscles will cause the body to bend forward at the waist, the head to drop down on the chest, the arms to bend at the elbow or the knees to come up to the chest. An abrupt increase in tone in the extensor muscles will cause the head to be thrown back, the back to arch, the legs to extend, the arms to stiffen. Any or all of these movements may occur during a myoclonic jerk. If they occur while a child is standing, he may be suddenly thrown back to the ground, or he may suddenly be thrown forward to the ground, perhaps hitting his/her face, breaking a tooth, or causing a facial laceration.