Pediatric Movement Disorders - Myoclonus

Examination

As with other movement disorders, it is important to determine which parts of the body are affected by myoclonus. It may occur in a single limb, the neck, the back, or the face. In other cases, it may affect the entire body. When severe, myoclonus may cause the child to fall. It is important to determine whether symptoms improve or worsen with voluntary activity. This is often tested by observing the child attempting to drink from a cup. In some cases, a myoclonic jerk may be caused by an unexpected, loud noise or a gentle tap on the tip of the nose or on the forehead.

To test for negative myoclonus, also known as asterixis, children are asked to extend their arms with the wrists back or to perform some other movement that requires holding the limb against gravity. In this way, a sudden loss of muscle contraction causes the hand or the arm to fall in a downward direction. Since myoclonus may occur along with other movement disorders, it is important to look for evidence of dystonia, tremor, ataxia, or spasticity. It is also important to look for opsoclonus, which is a random, dance-like jerking of the eyes in all directions. This eye movement occurs in the opsoclonus-myoclonus-ataxia syndrome.