Myoclonus, referring to an involuntary lightning-fast quick jerk, has probably been experienced by all of us at one point or another, manifesting as the jerking of legs or body upon falling asleep.
This is a benign condition (known as hypnic jerks) and no cause for alarm. However, at times myoclonus may be more pronounced, present at all times of day, even disruptive. When myoclonus occurs while a limb is being held up it can look like a brief loss of tone, known as negative myoclonus. This can result in dropping things or even legs buckling and falls in rare cases. When myoclonus is more sustained or pronounced, an evaluation should be conducted to elucidate the underlying cause.
There is a long list of causes of myoclonus, including medications, kidney or liver failure, epilepsy, degenerative conditions such as dementia, and genetic causes. Sometimes the cause is not identified, and is known as essential myoclonus. The term “essential” means that the essence of the condition is myoclonus; it is another way of saying the myoclonus “is what it is”. The exam is otherwise normal, and the myoclonus tends to remain stable over the years. Essential myoclonus can be associated in families with essential tremor (ET) or a type of dystonia called myoclonus dystonia.
Treatment can include sedatives such as clonazepam and anti-epileptic medications (even though the myoclonus may not be caused by epilepsy) such as levetiracetam (Keppra), valproic acid (Depakote), phenytoin (Dilantin) or primidone.