Myoclonus describes both a symptom and a disease. Myoclonus arises from damage to the central nervous system, which comprises the brain and spinal cord. Myoclonus is activated by an electrical discharge originating in the central nervous system, which is transmitted through peripheral nerves to produce the sudden muscle contractions.
Myoclonic jerks can cause disability by interrupting normal posture or movement.
Recurrent or severe myoclonic jerking is characterized by frequent forceful uncontrollable muscle contractions of any body part, or the entire body, making independent motor function impossible. Patients severely afflicted with myoclonus may be unable to stand or ambulate, reach or grasp objects, feed or dress themselves, speak, or even direct their gaze because of the involuntary muscle jerking interfering with all of these functions. Myoclonus is often triggered by movement. Patients may manifest no myoclonus at rest or when asleep, yet may experience uncontrolled jerking when attempting to move. The brief positive muscle contractions of myoclonus are often accompanied with sudden, unexpected inhibitions of muscle contraction, or lapses of posture.