Propriospinal myoclonus revisited: Clinical, neurophysiologic, and neuroradiologic findings

The literature on propriospinal myoclonus (PSM) is poor and there are no systematic reviews of the subject. We sought to clarify the spectrum of PSM.

We first prospectively investigated all patients seen in our movement disorders clinic with a firm diagnosis of PSM between 2002 and 2007. All had a standardized interview, detailed clinical examination, laboratory investigations, comprehensive neurophysiologic examination, and spinal cord MRI, including diffusion tensor imaging with fiber tracking (DTI-FT). We also collected drug responses. Finally, we conducted a systematic review of the literature.

We enrolled 10 patients meeting the strict criteria for PSM, and also analyzed data on 50 patients from 26 previous reports. PSM occurred predominantly in male and middle-aged patients. The typical clinical picture consisted of myoclonic jerks consistently involving abdominal wall muscles, which worsen in the lying position. A premonitory sensation preceding the jerks and wake-sleep transition phase worsening were frequent. Most patients had a myoclonic generator at the thoracic level, with a myoclonus duration between 200 msec and 2 s. An underlying cause was infrequently found. DTI-FT detected cord abnormalities all of our patients.

The clinico-physiologic spectrum of propriospinal myoclonus (PSM) is homogenous. Involvement of the abdominal wall muscles, worsening in the lying position, premonitory sensation, and wake-sleep transition phase worsening are helpful clinical clues. Diffusion tensor imaging with fiber tracking appears more sensitive than conventional MRI for detecting associated microstructural abnormalities of the spinal cord. Symptomatic treatment of PSM is not straightforward, and clonazepam is reported to be the most effective drug. Zonisamide may be an interesting option.