Lecture 6 2/13/25 Flashcards
Where is ACTH produced?
anterior pituitary
What is the hypothalamic pituitary adrenal axis negative feedback loop?
-production of glucocorticoids by the adrenal glands initiates negative feedback at the hypothalamus
-negative feedback at the hypothalamus prevents hypothalamus from producing corticotropin releasing hormone (CRH)
-lack of CRH prevents anterior pituitary from producing ACTH
-lack of ACTH prevents adrenal glands from further producing glucocorticoids
What are the characteristics of the zona fasciculata?
-region of the adrenal gland that produces glucocorticoids/cortisol
-under hypothalamic-pituitary-adrenal regulation
-70% of cortisol is under HPA control
What are the normal functions of cortisol?
-carbohydrate, fat, and protein metabolism
-decreasing inflammation
-regulating blood pressure
-increasing glucose
-increasing appetite
What are the stimuli for the adrenal glands to make aldosterone?
-angiotensin II
-K+ (weak)
-ACTH (weak)
What are the functions of aldosterone on the kidney?
-increases absorption of sodium into the bloodstream; water follows
-increases excretion of potassium into the urine
-increases excretion of H+ into the urine
What is cushing’s syndrome?
excess circulating cortisol
What are the types of cushing’s?
-pituitary-dependent
-adrenal-dependent
-iatrogenic
-occult/atypical
-diet-stimulated
What is the signalment for cushing’s?
-older animals
-dogs older than 6; typically 9-11 years old
-female dogs
-cats between 4-17 years old
-cats that are also diabetic
Which dog breeds are predisposed to pituitary-dependent cushing’s?
**usually small/toy breeds
-poodle
-dachshund
-terrier
-beagle
-german shepherd
-boston terrier
-schnauzer
Which dog breeds are predisposed to adrenal-dependent cushing’s?
-poodle
-german shepherd
-dachshund
-labrador retriever
-terrier
-spaniel
-malamute
What are the common presenting signs of cushing’s?
-PU/PD
-polyphagia
-panting
-pot belly
-endocrine alopecia
-hepatomegaly
-muscle weakness
-systemic hypertension
What are some of the less common signs of cushing’s?
-lethargy
-hyperpigmentation
-bruising
-comedones
-thin skin
-poor hair regrowth
-urinary incontinence
-insulin resistance +/- diabetes mellitus
-calcinosis cutis
Which clinical signs can occur with cushing’s, but are uncommon as a primary sign?
-thromboembolism and respiratory distress
-ligament weakness and rupture
-pseudomyotonia/stiff back legs/ataxia
-facial nerve plasy
-CNS signs
-testicular atrophy
-persistent anestrus
What are the possible complications of cushing’s?
-UTI
-recurrent infections
-calcium oxalate urolithiasis
-hepatobiliary dz
Which changes can be seen on CBC in cushing’s patients?
-neutrophilic leukocytosis
-lymphopenia
-eosinopenia
-thrombocytosis
-mild erythrocytosis
Which changes can be seen on biochem in cushing’s patients?
-increased ALKP
-increased ALT
-increased GGT
-increased bile acids
-hypercholesterolemia
-hypertriglyceridemia
-hyperglycemia
-low BUN
-low T4
Which changes can be seen on UA in cushing’s patients?
-USG < 1.030
-proteinuria
-indicators of UTI
-possible pyuria/WBCs on sediment
-calcium oxalate crystals
What may be seen on radiographs in cushing’s patients?
-hepatomegaly
-calcified adrenal glands
-urinary calculi
-retroperitoneal hemorrhage
-bronchial calcification
-osteopenia
What may be seen on abdominal ultrasound in cushing’s patients?
-normal to large adrenals (PDH)
-small adrenals (iatrogenic)
-adrenal masses (ADH)
-hepatomegaly
Which type of cushing’s is most common?
pituitary-dependent
How do pituitary-dependent and adrenal-dependent cushing’s differ?
PDH: increased production of ACTH by the pituitary gland leads to increased cortisol production by the adrenal glands
ADH: adrenal glands make cortisol independent of ACTH; negative feedback leads to decreased ACTH production
What are the consequences of a pituitary tumor?
-increased ACTH
-increased cortisol
-no negative feedback from excess cortisol on the pituitary
What are the consequences of an adrenal tumor?
-adrenal produces excess cortisol independent of ACTH
-decreased ACTH production by the pituitary
What are the characteristics of pituitary-dependent cushing’s?
-most prevalent form
-normal to increased ACTH
-can occur with microadenoma or macroadenoma
-loss of feedback inhibition
-leads to adrenocortical hyperplasia
What are the characteristics of adrenal-dependent cushing’s?
-associated with adenoma, adenocarcinoma, and/or hyperplasia of the zona fasciculata
-autonomous secretion of cortisol leads to excess
-negative feedback response at the pituitary leads to low ACTH
What are the characteristics of iatrogenic cushing’s?
-due to exogenous intake of cortisol/glucocorticoids, such as pills, creams, and injections
-negative feedback response at the pituitary leads to low ACTH
What are the characteristics of food-dependent cushing’s?
-ACTH independent
-ectopic expression of GIP receptors is coupled to steroidogenesis
-marked periodic increase in postprandial cortisol
-ACTH is suppressed/low
Which type of cushing’s is most common in cats?
PDH
What are the key presenting signs of cushing’s in cats?
-diabetes mellitus
-alopecia
-thin, fragile skin
What are other potential signs of cushing’s in cats?
-PU/PD
-polyphagia
-abdominal distention
-muscle wasting
-weight loss or weight gain
What are some of the peculiarities of feline cushing’s?
-relatively uncommon in cats
-most have concurrent diabetes mellitus
-1/3 of cats have skin fragility
-recommended to do a 10x higher dose for LDDST
-only 1/3 of cats will have a positive ACTH stim test
-around 1/2 of cats have pituitary macroadenomas
When is weight loss vs weight gain seen in cushing’s cats?
-weight loss seen with unregulated diabetes mellitus concurrent with cushing’s
-weight gain seen with unregulated diabetes mellitus concurrent with acromegaly
What are the clin path abnormalities seen in cushing’s cats?
-hyperglycemia
-anemia
-hypochloremia
-hypertriglyceridemia
-normal total T4
-possible liver enzyme alterations; uncommon
Why is imaging not a typical first step to cushing’s diagnosis?
identification of adrenal or pituitary gland enlargement does not necessarily correlate with increased function
What are the treatment options for cushing’s in cats?
-surgery
-radiation therapy
-trilostane
When is an ACTH stim test done vs an LDDS test?
-ACTH stim in sick animals
-LDDST in healthy appearing animals
