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• Long duration asymmetrical postural tremor is likely to predict development of Parkinson’s disease a
  Elan D. Louis
  Published on: 7 January 2005

• Published on: 7 January 2005

  Long duration asymmetrical postural tremor is likely to predict development of Parkinson’s disease a

  • Elan D. Louis, Neurologist
  • Other Contributors:
    • Anjan Chatterjee

  Dear Editor,

  We read with interest the paper of Chaudhuri et al. [1] on long duration asymmetrical postural tremor. Like all thought-provoking research, the paper raises many questions that lend themselves to further research and thought.

  The issue of the relationship between ET and parkinsonism is complicated and this study underscores the need for further longitudinal research to clarify dise...

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  Dear Editor,

  We read with interest the paper of Chaudhuri et al. [1] on long duration asymmetrical postural tremor. Like all thought-provoking research, the paper raises many questions that lend themselves to further research and thought.

  The issue of the relationship between ET and parkinsonism is complicated and this study underscores the need for further longitudinal research to clarify disease progression and diagnosis. Broadly speaking, in a given cohort of patients with postural or kinetic tremor, what clinical features would most strongly predict the future development of parkinsonism? To give just one example, the authors have suggested asymmetry of the arm tremor as one such factor. Since arm tremor in ET may be mildly asymmetric [2], one avenue of inquiry might be to attempt to quantify the extent of this asymmetry that might reliably predict the later development of parkinsonism.

  A second related issue is the pathology of the two conditions and its relationship to the clinical diagnosis. ET probably represents a family of diseases united by the presence of action tremor, in the same way that Parkinsonism is a family of disorders united by a common set of clinical findings [3]. While we have some understanding of the subtypes of Parkinsonism, we do not have the same level of understanding of ET. Some subtypes of ET might in fact represent forms of Lewy body (LB) disease. We reported a patient with a clinical diagnosis of ET for more than forty years whose postmortem brain examination revealed a very focal presence of Lewy bodies in the locus ceruleus (not in the substantia nigra) representing an anatomically-restricted form of LB disease [4].

  Another possibility, given the clinical heterogeneity of ET is that, perhaps none of Chaudhuri’s patients had PD but rather, a form of ET whose pathology had eventually spread to the basal ganglia [5], resulting in clinical features of Parkinsonism (i.e., neither ET-PD or PD but a subtype of ET).

  Finally, we would like to end with a minor quibble. In an otherwise interesting and thought provoking paper the authors have concluded that asymmetric postural tremor may predict PD. While the authors clearly have shown that some patients with postural tremor go on to develop PD, their study design does not lend itself to the conclusion that asymmetric postural tremor predicts the development of PD. To determine risk (i.e., A “is likely to predict” B), one would have to start with a cohort with asymmetric postural tremor to see how many developed PD over time, comparing them to a cohort without this type of postural tremor. Future research using a prospective cohort of patients with tremor is indicated to confirm this clinical observation.

  References

  (1). Chaudhuri KR, Buxton-Thomas M, Dhawan V, Peng R, Meilak C, Brooks DJ. Long duration asymmetrical postural tremor is likely to predict development of Parkinson’s disease and not essential tremor: clinical follow up study of 13 cases. J Neurol Neurosurg Psychiatry 2005;76:115- 117.

  (2). Louis ED, Wendt KJ, Pullman SL, Ford B. Is essential tremor symmetric? Observational data from a community-based study of essential tremor. Arch Neurol 1998;55:1553-1559.

  (3). Louis ED. Essential tremor. The Lancet Neurology (In Press).

  (4). Louis ED, Honig LS, Vonsattel JPG, Maraganore DM, Borden S, Moskowitz CB. Essential tremor associated with focal non-nigral Lewy bodies: A clinical-pathological study. Arch Neurol (In Press).

  (5). Cohen O, Pullman S, Jurewicz E, Watner D, Louis ED. Rest tremor in essential tremor patients: Prevalence, clinical correlates, and electrophysiological characteristics. Arch Neurol 2003;60:405-410.

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  Conflict of Interest:
  None declared.

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