title: Poorer Cognitive Performance in Patients with Essential Tremor-Parkinson's Disease vs. Patients with Parkinson's Disease.
abstract: BACKGROUND
  Patients with essential tremor (ET) seem to be at increased risk of developing Parkinson's disease (PD). Surprisingly, little has been written about this clinical entity, ET-PD. Cognitive dysfunction is a well-known feature of PD, and can also be an issue in patients with ET. Whether the presence of the combined diagnosis, ET-PD, is associated with additive cognitive effects as compared with PD has not been studied.
  
  
  METHODS
  Thirty ET-PD patients and 53 age-matched PD patients were enrolled in a clinical-epidemiological study. Two cognitive screens, the Telephone Interview for Cognitive Status (TICS, score = 0-41) and Folstein Mini-Mental State Examination (MMSE; range 0-30), were administered.
  
  
  RESULTS
  The MMSE score was lower in ET-PD than PD [26.5 ± 3.1 (median 28.0) vs. 28.4 ± 2.2 (median 29.0), p = 0.001]. The TICS score was lower in ET-PD than PD [31.7 ± 3.9 (32.0) vs. 35.0 ± 2.0 (35.0), p < 0.001]. Subscores of these tests that related to orientation (p < 0.001), language (p < 0.001), and working memory (p = 0.001) were lower in ET-PD than PD, whereas the delayed memory subscore was only marginally lower in ET-PD than PD (p = 0.06), and the two groups did not differ with respect to the motor/construction subscore (p = 0.22). Both global cognitive scores were inversely correlated with disease duration (for MMSE score, Spearman's r = -0.46, p < 0.001; for TICS score, Spearman's r = -0.53, p < 0.001).
  
  
  CONCLUSIONS
  The combined diagnosis, ET-PD, seemed to be associated with additive cognitive effects as compared with PD alone.
authors.affiliation: Division of Movement Disorders, Department of Neurology, Yale School of Medicine, Yale University , New Haven, CT , USA ; Department of Chronic Disease Epidemiology, Yale School of Public Health, Yale University , New Haven, CT , USA.
authors.forename: Elan D
authors.initials: ED
authors.lastname: Louis
authors.affiliation: Division of Movement Disorders, Department of Neurology, Yale School of Medicine, Yale University , New Haven, CT , USA.
authors.forename: Brittany
authors.initials: B
authors.lastname: Rohl
authors.affiliation: Division of Movement Disorders, Department of Neurology, Yale School of Medicine, Yale University , New Haven, CT , USA.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Collins
authors.affiliation: Department of Neurology, College of Physicians and Surgeons, Columbia University , New York, NY , USA ; Taub Institute for Research on Alzheimer's Disease and the Aging Brain, College of Physicians and Surgeons, Columbia University , New York, NY , USA.
authors.forename: Stephane
authors.initials: S
authors.lastname: Cosentino
keywords: Parkinson’s disease; clinical; cognition; dementia; essential tremor