Myoclonic disorders of spinal origin.

Data in the literature on spinal myoclonic disorders are still scanty; little has been done to ensure an adequate classification; little is known about the pathophysiology of these disorders. Three patients with spinal myoclonic jerks are described, with detailed reference to electromyographic findings. On the basis of the case reports so far available, a classification into five subgroups is suggested of spinal myoclonic jerks: 1) after cord injuries; 2) associated with intramedullary cord tumours; 3) associated with intramedullary or extramedullary cysts; 4) associated with radiculomyelitis or myelopathy; 5) associated with affections of the alpha motoneurons. A number of hypotheses on the pathogenesis of this disorder are briefly discussed: peripheral or intraspinal sprouting, degeneration of alpha motoneurons or interneurons, reduction of the dendritic tree size, and involvement of the gamma system.