Propriospinal myoclonus: Clinical and polygraphic features in 5 cases

Propriospinal Myoclonus (PSM) is characterized by jerks arising within the cord and propagating rostrally and caudally at low velocity, probably along propnospmal pathways intrinsic to the cord. In the last years we have encountered 5 males aged between 41 to 73 years displaying the clinical and polygraphic features of PSM PSM had set in all without any recognizable trigger, and neurological examination and MRI of cord and brain were normal in all except one patient who had an arachnoid cyst at the level of the T9 left root. EMG showed that the jerks arose in spinally innervated muscles, usually the thoracic or lumbar segments; the jerks were thereafter propagated to rostral and caudal muscles at velocities of 3 to 16 m/s, according to a propriospinal pattern of propagation. Polygraphic studies showed that in 4 cases the jerks occurred quasirhythmically only during periods of relaxed wakefulness, when EEG alpha activity spread to anterior regions. Any mental activation and sleep inhibited the PSM. In the 5th case, some features of the restless legs syndrome were found, and the jerks lasted into light sleep. PSM responded partially to clonazepam or tramadol. PSM is a peculiar movement disorder arising in the spinal cord but subjected to supraspinal influences during the various wake and sleep stages. It may represent a cause of severe insomnia.