title: When do essential tremor patients develop head tremor? Influences of age and duration and evidence of a biological clock.
abstract: BACKGROUND
  Essential tremor (ET) is a chronic, progressive neurological disease. Head (neck) tremor may eventually develop in as many as 30-60% of patients, yet it is unclear why. Is its appearance merely a function of advancing disease duration? Alternatively, is patient age a primary factor? The latter would argue for the presence of a biological clock that is important for the expression of this clinical feature of ET.
  
  
  METHODS
  A total of 363 ET patients were enrolled in a cross-sectional, clinical-epidemiological study. Each ET patient underwent a 20-min videotaped neurological examination which included an assessment of the presence/absence of head tremor.
  
  
  RESULTS
  Head tremor was present on examination in 140 (38.6%) patients. Young patients, even with longer-duration tremor, rarely had head tremor: 2/27 (7.4%) patients<40 years old with tremor duration≥10 years had head tremor versus 121/283 (42.8%) older patients (>60 years old) with tremor duration≥10 years (p<0.001). In a multivariate logistic regression analysis, while head tremor was associated with age (p<0.001) it was not independently associated with tremor duration (p=0.26); interestingly, it was associated with gender in that model (p<0.001). With the exception of 1 patient, head tremor did not begin before the age of 36.
  
  
  CONCLUSIONS
  Data suggest that the appearance of head tremor in ET depends on a biological factor that is intrinsic to the patient (i.e. age) and is not a clear consequence of advancing disease duration.
authors.affiliation: G.H. Sergievsky Center, Department of Neurology, Columbia University, New York, NY 10032, USA. EDL2@columbia.edu
authors.forename: Elan D
authors.initials: ED
authors.lastname: Louis
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001683:Biological Clocks / Q000502:physiology; D003430:Cross-Sectional Studies; D018450:Disease Progression; D020329:Essential Tremor / Q000175:diagnosis* / Q000453:epidemiology*; D005260:Female; D019416:Head Movements / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013997:Time Factors; D055815:Young Adult