These involuntary hyperkinetic symptoms are described as discrete clinical phenomenon, readily distinguishable from the others. Although distinctions are made between chorea, athetosis, and dystonia, even their most prominent differences—the discreteness and rapidity of choreic movements and the slowness of athetotic ones—are more apparent than real. As pointed out by S.A. Kinnier Wilson, involuntary movements may follow one another in such rapid succession that they become confluent and therefore appear to be slow. In reality, they usually occur together or blend imperceptibly into each other and have many points of clinical similarity. There are reasons to believe that they have a common anatomic and physiologic basis although distinct sites in the brain have been tentatively implicated for each. One must be mindful that chorea, athetosis, and dystonia are symptoms and are not to be equated with disease entities that happen to incorporate one of these terms in their names (e.g., Huntington chorea, dystonia musculorum deformans). Here the discussion is limited to the symptoms. The diseases of which these symptoms are a part are considered mainly in Chap. 39.
Somewhat more ambiguous but in common clinical use is the term dyskinesia. It encompasses all the active movement phenomena that are a consequence of disease of the basal ganglia, usually implying an element of dystonia. It has also been used to refer more specifically to the undifferentiated excessive movements that are induced in Parkinson patients at the peak of L-dopa effect and to numerous dystonic and athetotic movements that may follow the use of neuroleptic drugs (“tardive dyskinesias”) that are discussed further on.
Derived from the Greek word meaning “dance,” chorea refers to involuntary arrhythmic movements of a forcible, rapid, jerky type. These movements may be simple or quite elaborate and of variable distribution. Although the movements are purposeless, the patient may incorporate them into a deliberate act, as if to make them less noticeable. When superimposed on voluntary actions, they may assume an exaggerated and bizarre character. Grimacing and peculiar respiratory sounds may be other expressions of the disorder. Usually the movements are discrete, but if very numerous, they become confluent and then resemble athetosis, as described below. In moments when the involuntary movements are held in abeyance, volitional movements of normal strength are possible; but they also tend to be excessively quick and poorly sustained. The limbs are often slack or hypotonic and because of this, the knee jerks tend to be pendular; in other words, with the patient sitting on the edge of the examining table and the foot free of the floor, the leg swings back and forth several times in response to a tap on the patellar tendon, rather than once or twice, as it does normally. A choreic movement may be superimposed on the reflex movement, checking it in flight, so to speak.
Chorea differs from myoclonus mainly with respect to the speed of the movements; the myoclonic jerk is much faster and may involve single muscles or part of a muscle as well as groups of muscles. Failure to appreciate these differences often results in an incorrect diagnosis. The hypotonia as well as the pendular reflexes that accompany chorea may also occur in disturbances of cerebellar function. Lacking, however, are “intention” tremor and true incoordination or ataxia. In some circumstances, it may be necessary to distinguish chorea from myoclonus.