General information of psoriasis in Western Medicine.docx
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GeneralinformationofpsoriasisinWesternMedicine
GeneralinformationofpsoriasisinWesternMedicine
1.1Definitionofpsoriasis
Psoriasisisachronic,inflammatoryandsystemicdiseasethatmanifestsmostcommonlyaswell-circumscribed,erythematouspapulesandplaquesontheskinthatarecoveredwithsilveryscales.Usuallytheskinlesionsarepruriticandpainfulwithadherentthickscales,removalofthesescalesmayrevealpinpointbleeding.Thediseaseisachronicrecurringconditionthatvariesinseverityfromminorlocalisedpatchestocompletebodycoverage.Nailsandjointscanalsobeaffectedbypsoriasis
(1).
1.2Pathologyandpathogenesisofpsoriasis
Theetiologyandpathogenesisofpsoriasishasnotbeencompletelydefinedbutitinvolvesimmunestimulationofepidermalkeratinocytes.Itinvolvesacompleximmunologicalandinflammatoryreaction
(1).Thepathogenesisofpsoriasishasalargehereditarycomponent.Atleasteightchromosomallocihavebeenidentifiedforwhichstatisticallysignificantevidenceforlinkagetopsoriasishasbeenobserved(theselociareknownaspsoriasissusceptibility(PSORS)1to8)
(1).Ofthesechromosomalloci,thehumanleukocyteantigen(HLA-Cw6allele/HLA-Cw0602–Cw0613),alsoknownasPSORS1,isthekeysusceptibilitygeneforpsoriasis
(2).Inadditiontogeneticfactors,environmentalfactorsincludinginfection,smoking,medications(e.g.betablockers,nonsteroidalanti-inflammatorydrugs(NSAIDs),antimalarials,terbinafine,calciumchannelblockers,lipid-loweringdrugs,etc),skininjury(Koebner’sphenomenon)andstressarethoughttoevokeaninflammatoryresponseandsubsequenthyperproliferationofkeratinocytes,resultinginpsoriasis(1,3).
Thedevelopmentofpsoriasisisthoughttoinvolvesthefollowingprocess:
∙T-cellsactivateandmigrateintotheskinafterelementsoftheinnateimmunesystemareactivated(keratinocytesanddendriticcells)(3,4);
∙FunctionalT-cellsincludingtype1helperTcells(Th1)andtype17helperTcells(Th17)growundertheinfluenceofcytokinessuchasinterleukin12(IL-12)andinterleukin23(IL-23)(3,4);
∙Pro-inflammatorycytokinessuchastumournecrosisfactor-α(TNF-α),IL-17andIL-22aresecretedbyTh1andTh17cellspromotingtheinflammatoryprocessinpsoriasis(3,4);
∙Localskincellsincludingendothelialcells,fibroblasts,andkeratinocytesenhancethecutaneousimmuneresponsethroughexpressionofadhesionmoleculesandothermediators(3,4).
Overall,psoriasisisanimmune-mediatedorgan-specific(skin,and/orjoint)inflammatorydiseaseinwhichintralesionalinflammationprimesbasalstemkeratinocytestohyperproliferateandperpetuatethediseaseprocess(3,4).
1.3Epidemiologyofpsoriasis
1.3.1Prevalenceofpsoriasisinglobalgeneralpopulation
Althoughpsoriasisoccursworldwide,itsprevalencevariesconsiderably(5).Itisreportedthattheaverageglobalprevalenceofpsoriasisisapproximately3%–4%.About15%-30%ofpsoriasissufferershavethesequelae‘psoriaticarthritis’,equatingtoapproximately0.5%–1%ofthetotalpopulation(6).Table(chapter1-1)presentstheprevalencedatareportedinrecentsurveys.
Table(chapter1-1)Prevalenceofpsoriasisbycountry
Country
%withpsoriasis
Samplesize
China(7)
0.47
17,345
UK(8)
1.9
7,520,293
France(9)
5.2
6,887
Norway(10)
8.5
18,747
USA(11)
2.2
27,220
USA(12)
3.15
2,984
USA(Caucasianpopulation)(13)
2.5
21,921
USA(Africanpopulation)(13)
1.3
2,443
Australia(Victoria)(14)
6.6
1,457
1.3.2Factorsimpactingontheprevalenceofpsoriasis
Thereportedprevalencesurveysdifferinmanyregards,namelygeographicaloriginofthestudy,definitionofprevalenceontimepoint,period,andlifetimeofpsoriasis,samplingmethods,andwhetheritisself-reportedordiagnosisconfirmedbyphysician.Mostofthesestudiesarebasedonself-reporteddiagnosis,whichmayleavemildcasesofpsoriasis,e.g.naildisease,undiagnosed.Moreover,theelusiveaetiologyofskindiseasesandthelackofpreciseclassificationcriteriaforpsoriaticarthritismayalsoleadtomisdiagnosis(6).
Geographicandethnicfactorsalsocontributetodifferencesinpsoriasisprevalence.Forinstance,theprevalenceincoolerregionsishigherthanthatofotherregions(15).Inaddition,lowerprevalenceisobservedamongAfricanAmericans(1.3%),comparedwiththeCaucasianAmericanpopulation(2.5%)(13).
Multi-factorialcomponentssuchasphysicalenvironment,geneticfactors,gender,ageandbehaviouralpatternsplayaroleintheprogressionofpsoriasis(15).
Ithasbeensuggestedthattheonsetofpsoriasisoccursatayoungerageinfemalepatientscomparedwithmales,whichresultsinahigherprevalenceinyoungfemalepatients(16).Furthermore,themeanageofonsetforthefirstpresentationofpsoriasisisbetween15–20years,withasecondpeakoftenoccurringbetween55–60years,andthenasignificantdeclineaftertheageof70years,irrespectiveofgender(16).
1.3.3Riskfactorsofpsoriasis
Theriskfactorsofpsoriasisarenotwelldefined.However,obesityisbelievedtobeassociatedwithpsoriasisaspatientshaveahigherbodymassindexcomparedwiththenon-psoriaticpopulation(17).Smokingislikelytoplayaroleintheonsetofpsoriasis(18)andalcoholmayinfluencetheprogressionofthedisease(19).Stressisanimportanttriggerfactorandmayinfluencethedevelopmentofthecondition(20).Furthermore,somemedicationsmaybeassociatedwiththeonsetorexacerbationofpsoriasis,includingantimalarialmedications,NSAIDs,β-blockers,lithiumsaltsandwithdrawalfromsteroids(21).Bacterialinfectionsmayalsotriggerorexacerbatepsoriasis(21).Conversely,theconsumptionoffruitandvegetables,carrots,tomatoesandβ-carotenecandecreasetheriskofpsoriasis(22).
1.3.4Impactofpsoriasis
1.3.4.1Qualityoflife
Psoriasisitselfisnotalife-threatingconditionhowever,ithasasignificantimpactonthesufferers’qualityoflife.Thepsychologicalcomorbiditiesofpsoriasiscansignificantlyimpairapatients’qualityoflife(23-25).Onestudycomparedqualityoflifeinpeoplewithpsoriasiswithpeoplewhohaveotherdiseases,andfoundthatthequalityoflifeofpatientswithpsoriasiswasmoreseverethanthatofpatientswithdiabetes,coronaryheartdiseaseandcancer(26).Besidesthepatient'sappearance,theamountoftimerequiredtotreatextensiveskinorscalplesionsandtomaintainclothingandbeddingadverselyaffectsqualityoflifeaswell.Inaddition,arthriticpsoriasiscanalsoresultinincreasinganddebilitatingjointpainandstiffnessandimpairedmovement(27).
1.3.4.2Economicburden
Generally,thecostofdiseaseconsistsofdirectcostsincludingdiagnosticprocedures,therapiesandhospitaladmissionsandindirectcostsincludingworkabsenteeism,earlyretirement,andunemployment.Thecostofpsoriasisisconsiderablebecauseofitslong-termduration.StudiesinGermanysuggestedthattheaverageannualcostsofmildpsoriasisvulgarisperpatientrangedfrom500€to2,000€andforseverediseasefrom4,000€to10,000€(28,29).Theindirectcostwasestimatedtobeabout1,600€perpersonperannum(29).AsurveyinvestigatingpatientswithpsoriasisintheUnitedKingdomindicatedthatanaveragepsoriasispatientwasabsentfromworkfor26daysayear.InAmerica,psoriasiscostsUS$11.3billioninhealthcareannually(whencalculatedat2%prevalence)andthelossinproductivityfrompsoriasisisaroundUS$16.5billionperyear(30).
1.4Diagnosisofpsoriasis
1.4.1Typesofpsoriasis
Psoriasisisclassifiedintosevencategories:
1.Plaquepsoriasis(psoriasisvulgaris)
Plaquepsoriasisisthemostcommontypeofpsoriasis,observedinapproximately80%to90%ofpatients
(1).Plaquepsoriasisappearsassharplymarginated,erythematouspatchesorplaqueswithacharacteristicsilvery-whitemicaceousscale(31).Theplaquesareroundorovalinshapeandaretypicallylocatedonthescalp,trunk,buttocksandlimbs,especiallyonextensorsurfacessuchastheelbowsandknees
(1).
2.Guttatepsoriasis
Typicalmanifestationisdew-drop-like,1to15mm,salmon-pinkpapules,usuallywithafinescale.Itisfoundprimarilyonthetrunkandtheproximalextremities.AhistoryofupperrespiratoryinfectionwithgroupAbeta-hemolyticstreptococcioftenprecedesguttatepsoriasis.Thediseaseismostcommonduringchildhoodoradolescenceandcantransitionintopsoriasisvulgaris(1,3).
3.Inversepsoriasis
Inversepsoriasiscommonlyappearsintheinframammaryandabdominalfolds,groin,axillae,andgenitalia.Thelesionsappearaserythematousplaqueswithsmallscales(1,3).
4.Naildisease
Thecharacteristicsofnailpsoriasisincludepitting,onycholysis,subungualhyperkeratosis,andtheoil-dropsign(atranslucentdiscolourationinthenailbedthatresemblesadropofoilbeneaththenailplate).Nailpsoriasisusuallyaffectsnailsonthehandsmoreoftenthanthefeet.Itisseenin90%ofpatientswithpsoriaticarthritis
(1).
5.Psoriaticarthritis
Psoriaticarthritisisaninflammatoryseronegativespondyloarthropathyassociatedwithpsoriasis.Thecharacteristicsofpsoriaticarthritisarestiffness,pain,swelling,andtendernessofthejointsandsurroundingligamentsandtendons(dactylitisandenthesitis).Theseverityofthearthritisusuallydoesnotcorrelatewiththeskindisease.Naildamageisverycommoninpsoriaticarthritis.Theradiographicfeaturesofpsoriaticarthritismainlyinvolvejointerosion,jointspacenarrowing,andbonyproliferation(32).
6.Pustularpsoriasis
Pustularpsoriasisconsistsofgeneralisedandlocalisedtypes.Generalisedpustularpsoriasisshowswidespread
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