Dermatology-Main皮肤病-11-20

DermatologyMain11-20Q11A25-year-oldwomancomestothephysicianwitharashonherbuttocks.Thelesionsbegan10daysagoandareassociatedwithintenseitchingandburning.Shehasattemptedtreatmentwithcoolcompressesandcalaminelotionwithoutrelief.Thepatienthashadoccasionaldiarrheaandunintentionalweightlossoverthepastfewmonths.Hermedicalhistoryisotherwiseunremarkable.Hertemperatureis37.1C(98.8F),bloodpressureis117/76mmHg,pulseis82/min,andrespirationsare14/min.Theskinlesionsareshownintheimagebelow.Whichofthefollowingisthemostlikelydiagnosisofthispatient’srash?A.BullouspemphigoidB.DemiatitisherpetiformisC.ErythemamultiformeD.HerpeszosterE.PemphigusvulgarisF.PsoriasisA11Correctanswer:BEffectmodificationresultswhenanexternalvariablepositivelyornegativelyimpactstheeffectofariskfactoronthediseaseofinterest.Itcansometimesbeconfusedwithconfounding：thebiasthatresultswhentheexposure-diseaserelationshipisobscuredbytheeffectofanextraneousfactorthatisassociatedwithboththeexposureanddisease.Effectmodificationcanbedistinguishedfromconfoundingbyperformingastratifiedanalysiscenteringonthevariableofinterest.Ifthevariableisaconfounder,therewillbenosignificantdifferenceinriskbetweenthestratifiedgroupsastheconfoundingeffectsarenowremoved.However,ifthevariableisinsteadaneffectmodifier,therewillbeasignificantdifferencebetweenthe2groups.Inthiscase：stratificationbyfamilyhistoryshowsthatoralcontraceptivessignificantlyincreasetheriskofbreastcancerinpatientswithapositivefamilyhistorybutnotinpatientswithanegativefamilyhistory.Thus,familyhistoryisnotaconfoundingvariable(ChoiceA).Rather,positivefamilyhistoryactsasaneffectmodifiertoincreasetheriskofbreastcancerinpatientstakingoralcontraceptives.Otherwell-knownexamplesofeffectmodificationincludetheeffectofestrogensontheriskofvenousthrombosis(augmentedbysmoking)andtheriskoflungcancerinpeopleexposedtoasbestos(alsoenhancedbysmoking).(ChoiceC)Thelatencyperiodisthetimerequiredforagivenexposuretohaveameasurableeffectontheoutcome.ThisstudyprovidednoInformationonhowlongoralcontraceptivesmustbeusedinordertohaveaneffectonbreastcancerriskinsusceptiblepatients.(ChoicesDandE)Flawsinastudyinvolvingsubjectenrollmentordatarecordingcanresultinselectionbiasorobserverbias,respectively.Effectmodificationisnotabias,butratheranaturalphenomenonthatisimportanttorecognize.Educationalobjective:Effectmodificationresultswhenanexternalvariablepositivelyornegativelyimpactstheeffectofariskfactoronthediseaseofinterest.Itcanbedistinguishedfromconfoundingbyperformingastratifiedanalysiscenteredonthevariableofinterest.Effectmodificationisnotabias,butratherisanaturalphenomenonthatisimportanttorecognize.Q12A26-year-oldwomancomestothephysicianforevaluationofalesiononherleftfootSheinitiallynoticedasmallbump6-7monthsagothathasgraduallybecomefirmandslightlypigmented.Shehasnopainoritchingaroundthesiteandhasnoothermedicalconditions.Thepatienthasnohistoryoftobaccooralcoholuse.Sheworksasanaccountant.Hertemperatureis36.1C(97F);bloodpressureIs128/76mmHg;andpulseis78/min.Skinexamination(shownbelow)revealsa0.8cmhyperpigmentednodulewithdarkedges.Thereisacentraldimplethatdevelopswhenthelesionispinchedattheedges.Theremainderofherphysicalexaminationiswithinnormallimits.Whichofthefollowingisthemostlikelydiagnosis?A.BasalcellcarcinomaB.DermatofibromaC.KaposisarcomaD.PyogenicgranulomaE.SquamouscellcarcinomaA12Correctanswer:BThispatient'sskinlesionisconsistentwithadermatofibroma(DF),whichisduetofibroblastproliferationcausingisolatedormultiplelesions：mostcommonlyonthelowerextremities.Theetiologyisunknown,butsomepatientsmaydeveloplesionsaftertraumaorinsectbites.Typicallesionsarenontenderandappearasdiscrete：firm,hyperpigmentednodulesthatareusually1cmindiameter.Thelesionshaveafibrouscomponentthatmaycausedimplinginthecenterwhentheareaispinched(dimpleorbuttonhole”sign).DiagnosisofDFismadeclinicallybasedontheappearanceofthelesion.Treatment(cryosurgeryorshaveexcision)isusuallynotrequiredunlessthelesionissymptomatic,bleeds,orchangesincolororsize.Patientsmayalsorequesttreatmentforcosmeticreasonsorbecauseofrecurrentcutswhenshavingthelegs.(ChoiceA)Basalcellcarcinomaisthemostcommontypeofskincancerandpresentsasapearlynodulewithsmalltelangiectasiasinsun-exposedareas.Althoughitcanbepigmented：basalcellcarcinomadoesnotdimpleinthecenterwhenpinchedandisuncommoninyoungpatients.(ChoiceC)Kaposisarcomaisduetohumanherpesvirus-8(HHV-8)andisfrequentlyseeninimmunocompromisedpatients(especiallyAIDS-related).Lesionsaretypicallymulticentric,red,purple,orbrownmacules,plaques：ornodulesthatcanappearonthetrunk,extremities,orface.(ChoiceD)Pyogenicgranulomaisabenignvascularskintumorthatpresentsasasmallredpapulethatgrowsrapidlyoverweeksormonthstoapedunculatedorsessileshinymass.Thelesionsmostcommonlyoccuronthelipandoralmucosaandcanbleedwithminortrauma.(ChoiceE)Squamouscellcarcinomaisthesecondmostcommonskincancerandusuallyoccursonsun-exposedareas.Typicallesionsarefirmandscalypapules,plaques,ornodulesthatdonotusuallyhaveacentraldimplewithpinching.Educationalobjective:Dermatofibromasarenontender.firm,hyperpigm