EDITORIAL
Propriospinal Myoclonus: Where Do We Go From Here? Peter Brown, MD* Nuffield Department of Clinical Neurosciences, University of Oxford, Level 6, West Wing, John Radcliffe Hospital, OX3 9DU, United Kingdom
Propriospinal myoclonus was first described in 1991 as axial jerks of spinal origin.1 The myoclonus differed from segmental spinal myoclonus in that many spinal segments were involved, putatively linked by activity in the axially focused propriospinal pathways that link distant spinal segments within the cord. As such, two additional key features of the myoclonus were that it spared the distal limbs and face, and that myotomes were recruited into the jerks from a spinal focus with relative latencies that were consistent with conduction in slow propriospinal pathways. This original description of propriospinal myoclonus was followed by a gamut of anecdotal and rather speculative reports relating this condition to diverse causes ranging from vitamin deficiency to cannabis exposure.2 These dominated over a steady trickle of more credible reports of propriospinal myoclonus related to causes already associated with spinal segmental myoclonus, such as spinal tumors, syringomyelia, spinal dural arteriovenous fistula, and infective myelitis.1,3-5 Enthusiasm for the diagnosis of propriospinal myoclonus has since waned. This has followed the realization that many cases of suspected propriospinal myoclonus are certainly psychogenic.2,6-8 This is evidenced by clinical features, but also confirmed by the presence of a Bereitschafts potential that starts before spontaneous jerks and is similar to that seen preceding voluntary movements.6-8 At the same time, the diagnostic value of a slow spinal recruitment order has been questioned as evidence of organicity, because a similar pattern can occur when young healthy subjects are trained to mimic jerks9 or in some patients with suspected psychogenic jerks.8 So where does this leave us? Is propriospinal myoclonus in fact a syndrome identified by phenotype, with several causes? Or is it that psychogenic jerks with the
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*Correspondence to: Dr. Peter Brown, Professor of Experimental Neurology, Nuffield Department of Clinical Neurosciences, University of Oxford, Level 6, West Wing, John Radcliffe Hospital, OX3 9DU, United Kingdom, E-mail: [email protected]
Funding agencies: Dr. Brown is funded by the Medical Research Council and the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre. Relevant conflicts of interest/financial disclosures: Nothing to report. Full financial disclosures and author roles may be found in the online version of this article. Received: 9 May 2014; Accepted: 5 June 2014 Published online 1 July 2014 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/mds.25959
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same characteristics as described in the original report of the condition are so common that there are inevitably instances in which independent co-pathology exists that has been mistakenly assumed to be causally related? The latter is the implication, if not the overt assertion, of the interesting report by Esposito et al. in this issue of Movement Disorders.2 The matter is of major clinical importance, because we may be wasting valuable resources investigating possible spinal pathological conditions in those with the propriospinal phenotype, when we should be concentrating on psychiatric assessment and early cognitive behavioral therapy. Esposito et al. provide good evidence that propriospinal myoclonus is a relatively rare accompaniment of spinal structural pathological conditions.2 No cases were found in their survey of 85 patients with such pathological conditions. But rarity is neither unfamiliar to the neurologist nor an argument for functional causes. Consider classical painful tonic spasms in multiple sclerosis, an acknowledged manifestation of spinal pathological conditions. Espir and Millac10 found only five cases out of 600 patients (
Propriospinal Myoclonus: Where Do We Go From Here? Peter Brown, MD* Nuffield Department of Clinical Neurosciences, University of Oxford, Level 6, West Wing, John Radcliffe Hospital, OX3 9DU, United Kingdom
Propriospinal myoclonus was first described in 1991 as axial jerks of spinal origin.1 The myoclonus differed from segmental spinal myoclonus in that many spinal segments were involved, putatively linked by activity in the axially focused propriospinal pathways that link distant spinal segments within the cord. As such, two additional key features of the myoclonus were that it spared the distal limbs and face, and that myotomes were recruited into the jerks from a spinal focus with relative latencies that were consistent with conduction in slow propriospinal pathways. This original description of propriospinal myoclonus was followed by a gamut of anecdotal and rather speculative reports relating this condition to diverse causes ranging from vitamin deficiency to cannabis exposure.2 These dominated over a steady trickle of more credible reports of propriospinal myoclonus related to causes already associated with spinal segmental myoclonus, such as spinal tumors, syringomyelia, spinal dural arteriovenous fistula, and infective myelitis.1,3-5 Enthusiasm for the diagnosis of propriospinal myoclonus has since waned. This has followed the realization that many cases of suspected propriospinal myoclonus are certainly psychogenic.2,6-8 This is evidenced by clinical features, but also confirmed by the presence of a Bereitschafts potential that starts before spontaneous jerks and is similar to that seen preceding voluntary movements.6-8 At the same time, the diagnostic value of a slow spinal recruitment order has been questioned as evidence of organicity, because a similar pattern can occur when young healthy subjects are trained to mimic jerks9 or in some patients with suspected psychogenic jerks.8 So where does this leave us? Is propriospinal myoclonus in fact a syndrome identified by phenotype, with several causes? Or is it that psychogenic jerks with the
------------------------------------------------------------
*Correspondence to: Dr. Peter Brown, Professor of Experimental Neurology, Nuffield Department of Clinical Neurosciences, University of Oxford, Level 6, West Wing, John Radcliffe Hospital, OX3 9DU, United Kingdom, E-mail: [email protected]
Funding agencies: Dr. Brown is funded by the Medical Research Council and the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre. Relevant conflicts of interest/financial disclosures: Nothing to report. Full financial disclosures and author roles may be found in the online version of this article. Received: 9 May 2014; Accepted: 5 June 2014 Published online 1 July 2014 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/mds.25959
1092
Movement Disorders, Vol. 29, No. 9, 2014
same characteristics as described in the original report of the condition are so common that there are inevitably instances in which independent co-pathology exists that has been mistakenly assumed to be causally related? The latter is the implication, if not the overt assertion, of the interesting report by Esposito et al. in this issue of Movement Disorders.2 The matter is of major clinical importance, because we may be wasting valuable resources investigating possible spinal pathological conditions in those with the propriospinal phenotype, when we should be concentrating on psychiatric assessment and early cognitive behavioral therapy. Esposito et al. provide good evidence that propriospinal myoclonus is a relatively rare accompaniment of spinal structural pathological conditions.2 No cases were found in their survey of 85 patients with such pathological conditions. But rarity is neither unfamiliar to the neurologist nor an argument for functional causes. Consider classical painful tonic spasms in multiple sclerosis, an acknowledged manifestation of spinal pathological conditions. Espir and Millac10 found only five cases out of 600 patients (
