title: Nigrostriatal dopaminergic function in subjects with isolated action tremor.
abstract: BACKGROUND
  Isolated action tremor (IAT) is the hallmark clinical feature of essential tremor (ET), but it may also be a prominent feature of some individuals with Parkinson's disease (PD) suggesting a pathogenic relationship between these two disorders.
  
  
  OBJECTIVE
  We investigated the integrity of the striatal presynaptic dopaminergic system in subjects presenting IAT to improve the diagnostic accuracy and to explore any putative relationships between ET and PD.
  
  
  METHODS
  The striatal dopaminergic system was examined by means of dopamine transporter imaging using (123)I-(fluoropropyl)-2ß-carbomethoxy-3ß-(4-iodophenyl) nortropane ([123I]-FP-CIT) single-photon emission tomography (DAT-SPECT) in a clinical series of individuals with IAT, excluding those with associated resting tremor and bradykinesia.
  
  
  RESULTS
  Among 167 incidental individuals with IAT eligible for DAT-SPECT (Male/Female = 58.9/41.1%; Age = 67.8 ± 14.3 years), reduced striatal uptake was observed in 114 out of 167 (68.3%), whereas normal striatal binding was observed in the remaining 53 subjects (31.7%). Onset of tremor after 50 years and asymmetrical distribution of tremor were predictive variables of nigrostriatal denervation, whereas gender, family history and the presence of intentional, cephalic or voice tremors were not associated with nigrostriatal denervation.
  
  
  CONCLUSIONS
  Our findings suggest that IAT is a frequent presenting symptom in a subset of individuals with PD, often misdiagnosed as ET, and that DAT-SPECT can help differentiate between these two disorders. Current diagnostic criteria for ET should be revised to include asymmetry and late-onset tremor as predictors of nigrostriatal denervation.
authors.affiliation: Services of Neurology, Son Espases University Hospital, Mallorca, Spain. fcoriab@meditex.es
authors.forename: Francisco
authors.initials: F
authors.lastname: Coria
authors.forename: Marta
authors.initials: M
authors.lastname: Gimenez-Garcia
authors.forename: Lluis
authors.initials: L
authors.lastname: Samaranch
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Mora
authors.forename: Catalina
authors.initials: C
authors.lastname: Sampol-Bas
authors.forename: Pau
authors.initials: P
authors.lastname: Pastor
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D003342:Corpus Striatum / Q000000981:diagnostic imaging* / Q000502:physiology; D059290:Dopaminergic Neurons / Q000000981:diagnostic imaging* / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013378:Substantia Nigra / Q000000981:diagnostic imaging* / Q000502:physiology; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods; D014202:Tremor / Q000000981:diagnostic imaging* / Q000503:physiopathology; D055815:Young Adult