[Abdominal propriospinal myoclonus of unknown etiology]

We report the case of a 77-year-old woman with a two-year history of abdominal non rhythmic myoclonus. Neurological examination was normal. Bursts of myoclonic activity were recorded from the rectus abdominis muscle and then from the external oblique muscle after a delay of 40 ms. Magnetic resonance imaging of dorsal spine revealed T7-T8 and T9-T10 disc protrusions without root compression. Electroencephalography, back-averaging-EEG, brain computed tomography scan, motor and sensory evoked potentials revealed no abnormality, thus ruling out the possibility that the myoclonic jerks might be of cortical origin. Electromyography of the rectus abdominis and external oblique and of the T7-T8 paraspinal muscles did not show signs of denervation. Therefore a peripheral origin of the myoclonus could be excluded. In our patient the difference in latency of the EMG activity between the external oblique and the rectus abdominis muscles was possibly due to the caudal propagation of the myoclonus by slowly conducting pathways, supporting the hypothesis for its propriospinal origin, even though a known ethiologic factor could not be identified.