title: Action tremor in Parkinson's disease: frequency and relationship to motor and non-motor signs.
abstract: OBJECTIVE
  Action tremor may occur in patients with Parkinson's disease and cause misdiagnosis with other movement disorders such as essential tremor and dystonia. Data on the frequency of action tremor in Parkinson's disease and on the relationships with other motor and non-motor signs are limited.
  
  
  METHODS
  A cross-sectional study of 237 patients with Parkinson's disease staging 1-2 on the Hoehn-Yahr scale was conducted. Data on action tremor and other motor and non-motor signs were collected using the Unified Parkinson's Disease Rating Scale part III and the Non-Motor Symptoms Scale.
  
  
  RESULTS
  Action tremor was found in 46% of patients and was associated with both severity of rest tremor (adjusted odds ratio 3.0, P < 0.001) and severity of rigidity (adjusted odds ratio 1.5, P = 0.004). No association was found between action tremor and severity of bradykinesia (adjusted odds ratio 0.97, P = 0.4) or axial symptoms (adjusted odds ratio 0.9, P = 0.3). Moreover, patients who had action tremor reported a significant lower mean number of non-motor symptoms than those who had not (2.1 ± 1.3 vs. 2.4 ± 1.3; P = 0.04).
  
  
  CONCLUSIONS
  Action tremor is a relatively frequent motor sign in patients with Parkinson's disease staging 1-2 on the Hoehn-Yahr scale. Action tremor correlates with rest tremor and rigidity and may be associated with a lower burden of non-motor symptoms. These findings suggest a contribution of non-dopaminergic mechanisms to action tremor pathophysiology.
authors.affiliation: Department of Basic Medical Sciences, Neurosciences and Sensory Organs, 'Aldo Moro' University of Bari, Bari, Italy.
authors.forename: A F
authors.initials: AF
authors.lastname: Gigante
authors.forename: G
authors.initials: G
authors.lastname: Bruno
authors.forename: G
authors.initials: G
authors.lastname: Iliceto
authors.forename: M
authors.initials: M
authors.lastname: Guido
authors.forename: D
authors.initials: D
authors.lastname: Liuzzi
authors.forename: P V
authors.initials: PV
authors.lastname: Mancino
authors.forename: M F
authors.initials: MF
authors.lastname: De Caro
authors.forename: P
authors.initials: P
authors.lastname: Livrea
authors.forename: G
authors.initials: G
authors.lastname: Defazio
mesh_terms: D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D018476:Hypokinesia / Q000209:etiology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000150:complications / Q000503:physiopathology*; D012720:Severity of Illness Index; D014202:Tremor / Q000209:etiology / Q000503:physiopathology*
keywords: Parkinson's disease; action tremor; bradykinesia; non-motor symptoms; rest tremor; rigidity