Overview of Myoclonus
The term myoclonus comes from the Greek words for muscle (myo) and tumult (clonus) and refers to sudden, brief, shock-like movements. These movements may be "positive" or "negative." Positive myoclonus results in contraction of a muscle or multiple muscles. In asterixis, or negative myoclonus, there is a brief loss of muscle tone and then the tightening (contraction) of other muscles; this results in a flapping-type motion. These movements, which cannot by stopped at will (nonsuppressible), often have a characteristic saw-tooth pattern, and they usually disappear during sleep.
William A. Hammond, an early American neurologist, published a paper in 1873 on convulsive tremor in the American Journal of Sanity. He described a patient with what later came to be known as myoclonus. Nikolaus Friedreich is credited with publishing the first description of the disorder in 1881. He used the term paramyoklonus multiplex, which means "quick movements of the muscle in multiple places." These muscle jerks occurred in a 50-year-old patient.