normallevelsofcortisol.
Unfortunately,thetumor’s
secretionofACTHisnotturnedoff
bythecortisolsothetextmessages
keeparrivingtellingtheadrenalto
secretemorecortisol.
OthercasesofCushing’saredue
toadrenaltumorsthatsecretecortisoleventhoughthey
haven’treceivedtheACTHtextmessagefromthepituitary.
Finally,thesymptomsofCushing’scanalsobe
inducedbytreatmentofadogwithglucocorticoidsfor
allergy,inflammation,autoimmunedisease,orcancer.
Intheend,Cushing’sisadiseasecausedbytoomuch
corticosteroids.TheclinicalsignsofCushing’sdiseaseare
largelyduetotheeffectsoftheexcesscorticosteroidson
multipleorgans.Intheliver,cortisolincreasesglucose
synthesisandactivatesanti-stressandanti-inflammatory
pathways.Theresultinghighbloodglucoseleadstoinsulin
secretionfromthepancreas,whichcausesincreasedfat
synthesisandabdominalobesity.Muscleandskinweakens
becausecortisolleadstoincreasedproteinbreakdown
inthosetissues.Cortisolalsoinhibitsthesecretionof
vasopressinbythepituitary.Lowvasopressinlevelscauses
increasedurineproduction,whichleadstoincreasedthirst.
Cortisolalsoreducesboneformation,whichcause
osteoporosisinthelongterm.
“OnceJoujouwasdiagnosedshebecameravenouslyhungryall
thetimeandwasdrinkingwhatseemedlikegallonsatatime.”
ThefirstindicationsthatadogmighthaveCushing’s
syndromeareusuallyexcessivethirst(polydipsia),increased
urination(polyuria)andpanting.Alopecia(hairloss)over
theflanks,skinproblemsandincreasedappetiteareother
commonpresentingcomplaints.An
affecteddogmayalsoexhibita
droopingabdomenduetoweakened
abdominalmusclescombinedwith
increasedfatdeposition.Thetoptwo
photosaboveshowtheseverehairloss
andpotbellysufferedbyJoujou.
Cushing’ssyndromeisusuallyseeninolderdogs,witha
meanageatfirstdiagnosisof10.5years.Onsetisnoteasily
noticedandisslowlyprogressive.Itisseeninbothmales
andfemalesofalldogbreeds,withanincidenceofabout
onetotwocasesper1,000dogsperyear.Analysisofmore
than25,000dogsevaluatedover15yearsattheUniversity
ofCalifornia-DavisVeterinaryMedicalTeachingHospital
showsthattheincidenceofCushing’sinpurebreddogsis
nogreaterthaninmixedbreeds.Thereisnoevidencefor
inheritanceofapredispositionforCushing’sinthePBGV.
“IhavehadtwodogsdiagnosedwithCushing’s...bothwere
pickeduponroutinescreening.Onedogwasdiagnosedat13and
diedofothercausesat15.Theotherwasdiagnosedat12years
ofageandisstillwithusat17.”
HowisCushing’sdiagnosed?IfCushing’sis
suspected,adogwilltypicallybesubjectedtoacomplete
bloodcount,serumbiochemistrypanelandurinalysis.
Diagnosisisusuallyconfirmedbymeasurementofcortisol
inbloodatvarioustimesafteradministrationofapotent
syntheticcorticosteroid.Inahealthydog,thesynthetic
corticosteroidwillsuppresstheACTHsecretionbythe
pituitaryandsubsequentcortisolsecretionbytheadrenal.
Adogwithapituitarytumorwillexhibitlesssuppression
duetothesyntheticcorticosteroid,whereasadogwithan
adrenaltumorwillexhibitno
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SaberTails
IWinter2014
www.pbgv.org
27
Left:TwophotosofJoujoubefore
treatment,and,bottom,Joujouafter
beginningtreatmentforCushing’s
syndrome.Thephotobottomleft
showsthebeginningofJoujou’snew
hairgrowth.Bottomcentershows
Joujouabout21/2monthsonher
maintenancedoseoftrilostane.She
isdoinggreat.Shefeelsgood,and
hasmorehairthansheeverhad.