A preliminary look at the percentage of patients with Restless Legs Syndrome who also have Parkinson Disease, Essential Tremor or Tourette Syndrome in a single practice

Therapeutic studies, dopamine receptor blocking studies andPositronEmissionTomographic(PET)scanstudiesimplicatethe dopaminergic system in the pathogenesis of the RestlessLegsSyndrome(RLS)(Comella,2002;Eisensehret al.,2001;Michaud et al., 2002; Ruottinen et al., 2000; Staedt et al.,1993;Trenkwalderet al.,1999;Turjanskiet al.,1999;Walterset al.,1991).Itisthereforeofinteresttodeterminewhetherawell-proven dopaminergic disorder, Parkinson Disease (PD),predisposes to RLS, but results of such inquiries have beencontroversial (Krishnan et al., 2003; Ondo et al., 2002; Tanet al.,2002)andnotincompatiblewiththelargeprevalenceofRLSinthegeneralpopulation(Phillipset al.,2000).Therehavebeennopreviousstudieslookingatthereverseprevalence, i.e. the prevalence of PD in RLS. In the currentstudywetakeapreliminarylookatthepercentageofpatientswithRLSwhohavePDinasinglepractice.Tourette Syndrome (TS) is also responsive to eitherdopamineantagonistsoragonistsandRLShasbeenreportedinupto59%ofpatientswithTS(Lipinskiet al.,1997).Thesedata also suggest a dopaminergic hypothesis for RLS. Wethereforelookatthereverseprevalence,i.e.thatofTSinRLSintheaforementionedpractice.PreviousliteraturesuggestsanincreasedprevalenceofRLSin Essential Tremor (ET) (Larner and Allen, 1997) and asubset of patients with ET may be at increased risk for PD(Jankovic,2002).ThisindirectevidencealsosuggeststhatthedopaminesystemmayalsobeinvolvedinRLS.We,thereforealsoagainlookatthereverseprevalenceofETinRLSintheaforementionedpractice.Insummary,basedupontheaforementionedliterature,theproposedaimofthecurrentstudyistotakeapreliminarylookto see if RLS predisposes to other neurologic disordersinvolving the dopaminergic system. We want to emphasizethatthecurrentstudyisnotatrueprevalencestudysinceourpopulationis(a)small,(b)notpopulationbasedand(c)wedonothaveacontrolgroup.All RLS patients currently in the practice of a singleneurologist(ASW)withexpertiseinbothMovementandSleepDisorderswereexaminedforthepresenceofPD,TS,andETatthetimeofreferralforRLS.RLSwasdiagnosedbythefourcriteria established by the International Restless Legs Syn-dromeStudyGroup(Walters,1995).PDwasdiagnosedbythepresenceofbradykinesia,rigidity,restingtremor,andposturalinstability. TS was diagnosed by the presence of motor andvocal tics. ET was diagnosed by the presence of tremor thatwas predominantly a non-intention postural action type andthe absence of any features suggesting PD or cerebellar/spinocerebellardisease.OnlypatientswhowerereferredforRLSwereenteredintothestudy.RLSpatientswereexcludedwhowerereferredforPD,TS,orET.BecauseourdatasuggestedamildincreasedpercentageofPDinRLS,wealsoexcludedtwopatientswhowerereferredforRLSorsleepdisturbance,butwhohadPDatthe time of referral. This was done to exclude the possibilitythatapatientwithbothPDandRLSwouldbemorelikelytobereferredtousthanelsewhere,asweserveasareferralcenterfor both disorders. Patients with atypical parkinsonism werealso excluded. Two patients were also excluded when thediagnosis(PDorET)wasuncertain.Forpurposesofcalculation,thesurveywasconductedatasingle time point in November, 2001. For all three disordersstudied(PD,TS,andET),wecomparedthepercentagesofourRLSpatientswhohadthesedisorderstoprevalencesfromtheliteraturetakingageandsexintoaccount(Table1).Theexactbinomialtestwasusedforcomparison.Tourette’ssyndromeisofjuvenileonsetandtheprevalencerateisfairlystableacrossadultagegroups.Therefore,TSwasdeterminedforall118ofour adult RLS patients of any age in the study (Table1).Because of the tendency for PD to be of later onset andbecause most studies in the literature use an age base of>50years, we conﬁned our survey for PD to our 85 RLSpatients>50yearsofage(Table1).Becauseofthetendencyfor ET to be of later onset and because most studies in theliterature use an age base of >60years, we conﬁned oursurvey for ET to our 56 RLS patients >60years of age(Table1).After exclusion, four (three males, one female) or 4.7% ofour85(47females,38males)RLSpatients>50yearsofagedevelopedPDafterbeingreferredforRLS(Table1).Allhadat least stageII PD at the time of the survey indicating