Rhythmic myoclonias including spinal myoclonus.
In rare cases, rhythmic limb movements may appear in association with palatal myoclonus. There is a similar slow rate, below 4/sec. A review by Rondot and Ben Hamida (33) showed that the limb movements had much in common with postural tremors. Lhermitte and Sigwald (23) observed a peculiar pattern of upper limb oscillations in a patient with palatal myoclonus. It resembles a rare type of slow postural tremor, often called rubral tremor, described by Holmes (19). We found that a large group of alcoholics, showing signs of cerebellar degeneration, exhibit a stereotyped pattern of slow, coarse leg oscillations. There is a stable rhythm, in the 3/sec range, in alternating as well as in nonalternating muscle contractions. Both are in several maintained postures bicrurally synchronous, which is a feature of experimental and clinical myoclonus never observed in classic tremors. A few of these patients have upper limb oscillations, and these are of the kind described by Holmes (19) and Lhermitte and Sigwald (23). The cerebellar degeneration is of the anteromedial type; it is often associated with olivary changes (cerebelloolivary atrophy). Swanson et al. (40) and others included in the spinal category patients with myoclonus restricted to muscles innervated from one or more spinal cord segments and no recognizable neurological abnormality at higher levels. The most convincing cases of purely spinal origin are those in which segmental jerks are caused by a spinal tumor. These repetitive jerks may sometimes show a slow rhythm.