Temporal discrimination in patients with dystonia and tremor and patients with essential tremor

From the Department of Neurological, Psychological, Morphological and Motor Sciences (M.T., A.D.M., T.B., A.P., M.F.), University of Verona, Verona
Neurology (Impact Factor: 8.29). 12/2012; 80(1). DOI: 10.1212/WNL.0b013e31827b1a54
Source: PubMed


To investigate whether psychophysical techniques assessing temporal discrimination could help in differentiating patients who have tremor associated with dystonia or essential tremor.

We tested somatosensory temporal discrimination thresholds (TDT) and temporal discrimination movement thresholds (TDMT) in 39 patients who had tremor associated with dystonia or essential tremor presenting with upper-limb tremor of comparable severity and compared their findings with those from a group of 25 sex- and age-matched healthy control subjects.

TDT was higher in patients who had tremor associated with dystonia than in those with essential tremor and healthy controls (110.6 ± 31.3 vs 63.1 ± 15.2 vs 62.4 ± 9.2; p < 0.001). Conversely, TDMT was higher in patients with essential tremor than in those with tremor associated with dystonia and healthy controls (113.7 ± 14.7 vs 103.4 ± 11.3 vs 100.4 ± 4.2; p < 0.001). Combining the 2 tests in a pattern for essential tremor (abnormal TDMT/normal TDT) and tremor associated with dystonia (normal TDMT/abnormal TDT) yielded a positive predictive value (PPV) of 86.7% and a negative predictive value (NPV) of 70.8% for diagnosing essential tremor and a PPV of 100.0% and NPV of 74.1% for diagnosing tremor associated with dystonia.

TDT and TDMT testing should prove a useful tool for differentiating tremor associated with dystonia and essential tremor. Our findings imply that the pathophysiologic mechanisms underlying tremor associated with dystonia differ from those for essential tremor.

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Available from: Antonella Conte
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    • "Another measure for assessing somatosensory processing is the proprioceptive temporal discrimination motor threshold (TDMT), defined as the shortest interval at which the subject perceives two externally-induced passive movements as separate in time.[17] The TDMT is normal in patients with focal dystonia and abnormal in those with essential tremor (ET).[18], [19] Because ET probably involves the cerebellar and brainstem oscillating loops,[20] an abnormal TDMT could depend on cerebellar dysfunction. "
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    • "Tremor may be classified either as dystonic tremor or tremor associated with dystonia (TAWD) according to the Movement Disorder Society Consensus Statement (Deuschl et al., 1998). Similarities in phenotypic features of dystonic tremor and TAWD predominate over differences, suggesting that the two forms of tremor may be manifestations of the same disease (Defazio et al., 2013; Tinazzi et al., 2013). Differences in gender, body distribution and temporal thresholds of tremor between patients with dystonia and tremor and those of patients with essential tremor also indicate that tremor in dystonia and essential tremor are different entities (Defazio et al., 2013; Tinazzi et al., 2013). "
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    • "The STDT was investigated by delivering paired stimuli starting with an ISI of 0 ms (simultaneous pair), and progressively increasing the ISI in 10 ms steps, according to the experimental procedures used in previous studies (Scontrini et al., 2009, 2011; Conte et al., 2010, 2012b; Rocchi et al., 2013; Tinazzi et al., 2013). Paired tactile stimuli consisted of square-wave electrical pulses delivered with a constant current stimulator (Digitimer DS7AH) through surface skin electrodes with the anode located 0.5 cm distally to the cathode applied on the volar surface of the index finger of the left and right hand. "
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