Y
ourPBGVbeginstodrinkmorewaterandhastogooutmore
often.Thesearesymptomsthatwillleadtoavisittothevet,
wherecompletebloodworkandurinalysiswillbeconducted.
However,excessivethirst(polydipsia)andincreasedurination
(polyuria)aresymptomsthatareseeninmultipledisease
processes.Aphysicalexamandroutinetestscandetermineif
theyarecausedbydiabetes,kidneydisease,pyometra(uterine
infection)ortheuseofcertainmedications.Oncethosepossibilities
areeliminated,furthertestscanbeconductedtodetermineifthe
doghasprimaryliverdiseaseorCushing’ssyndrome.
WhatisCushing’ssyndrome?Cushing’sisanendocrine
diseasecausedbyexcessivesecretionbythepituitaryofahormone
calledadrenocorticotropichormone(ACTH).Unfortunately,
Cushing’sisnotsimpletodiagnosebecausesomanydifferent
organscanbeaffected.Tounderstandthecomplexityof
Cushing’s,letusfirstlookattheroleofACTHinthehealthydog.
Inahealthydog,astresscausesthepituitaryglandinthebrain
tosecretethehormoneACTH[seeFigure1atright].Ahormoneis
amoleculethatissecretedbyaglandandtransportedthroughout
thebodytodeliveritsmessagetootherglands.ACTHdeliversits
messagesolelytotheadrenalgland,informingitofthestressful
situation.Itisasifthepituitaryhassentaprivatetextmessageto
theadrenalgland,whichnootherglandreceives.
Theadrenalglanddoesnotkeepthismessageasecret;instead,
itspreadsthemessagebysecretingitsownsetofhormones,
knownascorticosteroids.Thecorticosteroidsincludebothinflam-
matoryhormones(aldosterones)andanti-inflammatoryhormones
(cortisol).Corticosteroidsbroadcastthestressmessagetomultiple
organsthroughoutthebody.Theprivatetextmessagehasbecome
averypublictweet!Thistweettellsthebodytofocusonsurviving
thestressratherthancarryingoutitsnormalmetabolicfunctions.
Forexample,cortisolcalmsthedog,turnsoffunnecessary
physiologicalfunctionsandprepareshim/hertoreacttothestress.
Thepituitaryalsoreceivesthistweet,recognizesthatitstext
messagehasbeenreceivedandshutsdownfurtherACTHsecretion.
WhatcausesCushing’s?Therearethreemajorformsof
Cushing’ssyndrome.Morethan90percentofcasesindogsare
duetobenign,slow-growingtumorsinthepituitary.Thetumors
secretehighlevelsofACTHinanunregulatedmanner[Figure1].
ThehighACTHstimulatestheadrenaltosecretehigherthan
26
www.pbgv.org
Winter2014
ISaberTails
IPBGVHealthReport
byLauraLiscum,PBGVCAHealthCommittee
LivingwithCushing’sSyndrome
“At11yearsofage,Joujouhadbecomeacouchpotato.Shewasdrinkingandurinatingalot.Wethought
shehadaurinarytractinfectionandhypothyroidism.Shewasalsostartingtoloseherhair.Bloodworkshowed
itwasmorethanjustthat,andwewerereferredtoaninternalmedicinespecialist.”
“Charlieturned11inJuly.Weknewsomethingwasupforthepastsixmonths.Hehadexcessivethirstand
hadlost5pounds.Wehadextensivebloodtests,butthevetwasunabletomakeadiagnosis.”
“Kikiwas13whenshebecameverythirstyandurinatedfrequently.Sheoftenurinatedinsidethehouse
despitebeingsolidlyhousetrainedformanyyears.”
“IhavehadtwodogsdiagnosedwithCushing’sinthelast20years.InPrincess’case,theonlyphysical
manifestationwaspantingatinappropriatetimes—inacoolhousewhilenotphysicallyactive.Acomplete
bloodcountshowedelevatedliverenzymesindicativethatsomethingwasgoingon.Webegandoingmore
testingwithCushing’sinmind,andshewasdiagnosedat13yearsoldwithapituitary-dependentCushing’s.”
Figure1.