This term designates uncontrollable, large amplitude, poorly patterned flinging movement of an entire limb. As remarked earlier, it is closely related to chorea and athetosis, indicated by the frequent coexistence of these movement abnormalities and the tendency for ballismus to blend into a less-obtrusive choreoathetosis of the distal parts of the affected limb. Ballistic movements are usually unilateral (hemiballismus) and the result of an acute lesion of or near the contralateral subthalamic nucleus or immediately surrounding structures (infarction or hemorrhage, less often a demyelinative or other lesion). Rarely, a transitory form is linked to a subdural hematoma or thalamic or parietal lesion. The flinging movements may be almost continuous or intermittent, occurring several times a minute, and of such dramatic appearance that it is not unusual for them to be regarded as hysterical in nature.
Bilateral ballismus is infrequent and usually asymmetrical; here a metabolic disturbance, particularly nonketotic hyperosmolar coma, is the usual cause. In combination with choreoathetosis, a paraneoplastic process is another rare cause. When ballismus persists for weeks on end, as it often did before effective treatment became available, the continuous forceful movements resulted in exhaustion, weight loss, and even death. In most cases, medication with haloperidol or phenothiazine suppresses the violent movements. In extreme cases, stereotactic lesions or implanted stimulating electrodes placed in the ventrolateral thalamus and zona incerta have proved effective (Krauss and Mundinger).
Dystonia is an unnatural spasmodic movement or posture that puts the limb in a twisted position. It is often patterned, repetitive or tremulous and can be initiated or worsened by attempted movement. There is unwanted overflow contraction of adjacent muscles and a common feature is involuntary co-contraction of agonist and antagonist muscles. Dystonia may take the form of an overextension or overflexion of the hand, inversion of the foot, lateral flexion or retroflexion of the head, torsion of the spine with arching and twisting of the back, forceful closure of the eyes, or a fixed grimace (Fig. 4-5).
Dystonia, like athetosis, may vary considerably in severity and may show striking fluctuations in individual patients. Dystonia may be limited to the facial, cervical, or trunk muscles or to those of one limb, and it may cease when the body is in repose and during sleep. Severe instances result in grotesque movements and distorted positions of the body; sometimes the whole musculature seems to be thrown into spasm by an effort to move an arm or to speak. In its early stages it may be interpreted as an annoying mannerism or hysteria, and only later, in the face of persisting postural abnormality, lack of the usual psychologic features of hysteria, and the emerging character of other aspects of an underlying illness, is the correct diagnosis made.
Causes of generalized dystonia (see Table 4-5) Generalized dystonia is seen in its most pronounced form as an uncommon heritable disease, dystonia musculorum deformans, which is associated with a mutation in the DYT gene. It was in relation to this disease that Oppenheim and Vogt in 1911 introduced the term dystonia. Dystonia also occurs as a manifestation of many other diseases, each of which is characteristic of a certain age group. These include the aforementioned double athetosis caused by hypoxic damage to the fetal or neonatal brain (a form of cerebral palsy), kernicterus, pantothenate kinase-associated neurodegeneration (formerly Hallervorden-Spatz disease), Huntington disease, Wilson disease, lysosomal storage diseases, striatopallidodentatal calcification (Fahr disease, sometimes caused by hypoparathyroidism), certain forms of thyroid disease, and exposure to neuroleptic drugs, as discussed below.