The clinical settings in which one observes widespread random myoclonic jerks as a transient or persistent phenomenon in adults is most often an acquired metabolic disorder (prototypically uremic and anoxic encephalopathy) and in certain drug intoxications, notably with haloperidol, lithium, and amphetamines. For example, an acute onset of polymyoclonus with confusion occurs with lithium intoxication; once ingestion is discontinued, there is improvement (slowly over days to weeks) and the myoclonus is replaced by diffuse action tremors, which later subside. A second broad category of acquired myoclonus consists of structural brain diseases such as viral encephalitis, Creutzfeldt-Jakob disease, syphilitic general paresis, advanced Alzheimer and Lewy body disease, corticobasal ganglionic degeneration, and occasionally Wilson disease. Table 4-7 lists these and others. A subacute encephalopathy with diffuse myoclonus may occur in association with the autoantibodies that characterize Hashimoto thyroiditis and also in Whipple disease. Diffuse, severe myoclonus may be a prominent feature of early tetanus and strychnine poisoning. Polymyoclonus that occurs in the acute stages of anoxic encephalopathy should be distinguished from postanoxic action or intention myoclonus that emerges with recovery from cardiac arrest or asphyxiation (it is discussed below). The factor common to all these disorders, with the exception of acquired metabolic disorders and intoxications, is the presence of diffuse neuronal disease.
Myoclonus in association with signs of cerebellar incoordination and opsoclonus (rapid, irregular conjugate eye movements in all directions as described in Chap. 13) is another syndrome of both children and adults. Most cases run a chronic course, waxing and waning in severity. Many of the childhood cases are associated with occult neuroblastoma, and some have responded to the administration of corticosteroids. In adults, a similar syndrome is well known as an effect of specific circulating antibodies that are elaborated in response to the presence of some tumors (“paraneoplastic,” mainly breast, and ovary as discussed in Chap. 30). The conduction also occurs as a self-limited manifestation of a postinfectious (usually viral) illness as described by Baringer and colleagues.
As mentioned above, diffuse myoclonus is a prominent and often early feature of the prion illness, Creutzfeldt-Jakob disease, characterized by rapidly progressive dementia, disturbances of gait and coordination, and all manner of mental and visual aberrations (see Chap. 32). Initially the jerks are random but late in the disease they may attain an almost rhythmic and symmetric character. In addition there is an exaggerated startle response, and violent myoclonus may be elicited by tactile, auditory, or visual stimuli in advanced stages of the disease. In yet another group of myoclonic dementias, the most prominent associated abnormality is a progressive deterioration of intellect. The myoclonic dementias may be sporadic or familial and may affect children or adults. A rare childhood type is subacute sclerosing panencephalitis (SSPE), which is an acquired subacute or chronic (occasionally remitting) disease related to a latent infection with the measles virus (see Chap. 32).