Hyperthyroidism

HyperthyroidismAnatomyThyroidglandisusuallytwoseparatelobesadjacenttofirstfiveofsixtrachealringsLieveryclosetothecarotidsheathandvagosympathetictrunkAccessorytissuecommonlyfoundinneckandtrunkHyperthyroidismMostcommonendocrinediseaseofcatsMostoftenthyroidadenomaorhyperplasiaAdenocarcinomasonlyin~2%ofaffectedcatsandmaymetastasizeDogsusuallyinactivemalignancyCatsusuallyfunctionalbutbenignHyperthyroidismFunctionalincreaseintissueproducesexcessthyroidhormoneSeeincreasedenergymetabolismBodyburnsthroughfuelfasterandsystemsfunctionathigherrateMultisystemiceffectssomosthaveclinicalsignsthatreflectdysfunctionofseveralorgansystems.SignalmentUsuallymiddleagedtooldercatsNobreedorsexpredilectionMostoftenslowlyprogressive~70%catshavebilaterallobeenlargementClinicallyWeightloss,unkempt,restless,can’tcopewithstress,increasedappetite,vomiting,diarrhea,PU/PDCanpalpateenlargementin~80%Systolicmurmur,galloprhythm,tachycardic                                                                       LabWorkCBC–directeffectontheerythroidmarrowandincreasedproductionerythropoietinChemistry–slightincreaseALT,AST,renaldysfunctionT3/T4levelsvary–25%normalT3butincreasedT4,2%bothnormalFreeT4–varywithregularT4testLabWorkInitialevaluationcanbeoffduetoconcurrentillnessasthyroidhormonemaybehighnormalorslightlyincreasedRenaldisease,diabetesmellitus,systemicneoplasia,primaryhepaticdiseaseRepeatbasalT4andruleoutconcurrentillnessRadionuclidetestingDependonthedietaryuptake,iodidedrugs,orcontrastagentRelativelyinsensitivediagnosticUsedtodeterminedoseoftherapeutic131IUsedtodetectmetastasis                      TreatmentOptionsLifelongmedicalmanagementSurgicalinterventionRadioactivetherapyMedicalManagementAimedtoblockiodinetotyrosylgroupofthyroglobinandpreventcoupleintoT4andT3LongtermgoalistomaintainT4inlownormalrangeatthelowestpossibledoseShorttermgoalistolowerT4concentrationbeforesurgicaloptionMedicalManagementMethimazole–managetheproblem,notcureDosefrom10-15mgperdaysoaslowerT4in2-3weeksCangoupto25-30mgperdayRecheckevery2-3weekstoallowadjustmentofthedoseMedicalManagementSideeffectsincludeanorexia,vomiting,lethargy,buttheseusualtransientandresolveselfinducedfacialexcoriationrarehepatictoxicityvarietyhemolyticabnormalitiesSurgicalInterventionMostoftencuresproblembutsignificantriskduesystemiceffectsofdiseaseprocessCanuseantithyroiddrugstolowerlevelspre-operativelytolowerrisksMustleaveparathyroidglandstocontrolcalciumhomeostasisSurgicalInterventionOptionofintracapsularorextracapsularremovalDorsalrecumbancywithforelegspulledcaudalandaventralmidlineincisionfromlarynxtomanubriumMustmaintainstricthemostasisorwilllosetheparathyroidglandsatcranialpoleSurgicalInterventionExtracapsular–removetheentirelobeafteridentifyingthejunctionoftheexternalparathyroidglandandthyroidtissueIntracapsular–nickincisionincapsuletoallowbluntremovaloftheparenchymaandremovalofasmuchcapsuleascanSurgicalInterventionSideeffectsincludehypoparathyroidismHorner’sSyndromelaryngealparalysishypercalcemiaRadioactiveTherapyNormallyinthebodyiodineonlygoestothethyroidglandRadioactiveiodineconcentratesinthehyperplasticorneoplastictissueanddestroysit131IhalflifeofeightdayssoanimalmustbekeptisolatedRadioactiveTherapyCatmustbeinmetaboliccagetocollectwasteasisradioactiveMinimalcontactDischargein1-3weeksNonoticedsystemiceffectsReferencesPeterson,ME,JFRandolph,andCTMooney.EndocrineDiseases.TheCat:DiseasesandClinicalManagement.2ndedvol2.EdRGSherdingDVM.Philidelphia:WBSaundersCo,1994.1412-Peterson,ME.Hyperthyroidism.TextbookofVeterinaryInternalMedicine.5thedvol2.EdEttinger,SJ,andECFeldman.Philidelphia:WBSaundersCo,2000.1400-http://www.vet.purdue.edu/vcs/scottmon/hyperthycat.htmlhttp://www.vin.com/VINDBPub/SearchPB/Proceedings/PR05000/PR00107.htmhttp://www.gcvs.com/imaging/feline_hyperthyroidism.htm