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.