Examples of myelitis with irregular and strictly segmental myoclonic jerks (either rhythmic or arrhythmic) have been reported in humans and have been induced in animals by the Newcastle virus. Many such myelitic cases involve the legs or a few muscles of one leg. In our experience, this type of myoclonus has occurred following zoster myelitis, postinfectious transverse myelitis, and rarely with multiple sclerosis, epidural cord compression, or after traumatic spinal injury. A paraneoplastic form has also been described, usually associated with breast cancer (see Chap. 30). When highly ionic contrast media was in the past used for myelography, painful spasms and myoclonus sometimes occurred in segments where the dye was concentrated by a block to the flow of spinal fluid.
Treatment is difficult and one resorts to a combination of antiepileptic drugs and benzodiazepines, just as in cerebral myoclonus. Levetiracetam reportedly has been successful when other drugs have failed (Keswani et al).
Focal myoclonus is also one of the notable features of degenerative neurologic conditions, particularly corticobasal ganglionic degeneration; it is generally seen in a limb that is made rigid by this process.
Under the title paramyoclonus multiplex, Friedreich, in 1881, described a sporadic instance of idiopathic widespread muscle jerking in an adult. It was probably in the course of this description that the term myoclonus was used for the first time. No other neurologic abnormalities accompanied the movement abnormality and its nature is obscure. We are not familiar with this process occurring in modern practice. Yet, there are many diseases in which multifocal or widespread asynchronous myoclonus is a manifestation, appropriately called polymyoclonus.
Several disparate disorders give rise to diffuse myoclonus. It may occur in pure or “essential” form as a benign, often familial, nonprogressive disease. A second broad category is allied with special forms of childhood epilepsy and there are several types that are associated with acquired neurologic diseases as discussed below, some quite serious in nature.
Symptoms may begin at any period of life but usually appear first in childhood. This disorder may be of the same nature as the one described by Friedreich, as mentioned above. An autosomal dominant mode of inheritance is evident in some families. The myoclonus takes the form of irregular twitches of one or another part of the body, involving groups of muscles, single muscles, or even a portion of a muscle. As a result, an arm may suddenly flex, the head may jerk backward or forward, or the trunk may curve or straighten. The face, neck, jaw, tongue, ocular muscles, and diaphragm may twitch. According to Wilson, even fascicles of the platysma may twitch. Some muscle contractions cause no visible displacement of a limb. Some patients register little complaint, accepting the constant intrusions of motor activity with stoicism; they generally lead relatively normal, active lives. Seizures, dementia, and other neurologic deficits are notably absent but several rare forms have been associated with axial dystonias. In a Mayo Clinic series reported by Aigner and Mulder, 19 of 94 cases of polymyoclonus were considered to be of this “essential” type.
Myoclonus in Epilepsy (See Also Myoclonic Seizures in Chap. 15)