Endocrine diagnostics and histology

In this hyperadrenocorticism = HAC, hypoadrenocoritism will be stated as HypoAC. Also includes steroid lecutre W3.

Identify the anatomy on this normal lateral radiograph

Green = stomach

Pink = liver

Orange = kidneys

Blue = spleen (ventral part)

Black = colon

Yellow = bladder

Middle = intestines

What view radiograph is this, identify the normal anatomy

• ventrodorsal

• red = liver

• green = stomach

• blue = spleen

• orange = kidneys

• black = colon

• yellow = bladder

• middle = intestines

Identify 10 features that signal to abnormal adrenals (HAC)

1. obesity

2. pot belly

3. hepatomegally - extends beyond the costal arch

4. ± adrenal mass

5. large bladder

6. ± cystoliths

7. dystophic mineralisation of soft tissues e.g. calcinosis cutis adrenal gland and/or kidney

8. ossteopenia (thinning bones)

9. excellent contrast b/w intraabdominal fat

What is an identifying feature of pituitary-dependent HAC

• hepatomegaly

What is a defining feature of hyperadrenocorticism

• contrast provided by intraabdominal fat

What is this structure?

• gall bladder

What is this structure?

• adrenal gland

What is the average width of adrenal glands with dogs who have pituitary-dependent HAC?

• 8.6mm

What are the blood vessel supply to the left adrenal?

• left phrenicoabdominal artery

• left phrenicoabdominal vein

• aorta with the cranial mesentaric artery and celiac artery branching off cranial to the adrenals

What is the blood supply to the right adrenal?

• phrenicoabdominal vein and artery

• caudal vena cava

• aorta also present

What are the abnormalities on this radiograph, what does it signal to?

• ‘‘mass effect’’, deviating colon, enlarged liver, stark contrast of organs due to fat

• adrenal dependent HAC

What is the ‘‘mass effect’’ abnormality on this radiograph, what condition does it signal to? (dog)

• deviating small intestine

• adrenal dependent HAC

What are the anatomical landmarks used to localise the left and right adrenal gland?

• celiac and cranial mesenteric arteries (left gland caudal, right gland cranial)

• cranial to renal artery

• phrenicoabdominal cein crosses mid portion of adrenal gland

• aorta (left), caudal vena cava (right)

What should the size of a normal adrenal gland be (dog and cat)?

• Dog varies with patient body weight - looking at the caudal pole of the adrenal gland

  • Left gland: 5.1 - 7.3 millimetres (smaller dog = smaller size vice versa)

  • right: 5.3-8.7mm

• Cats

• 2-5mm

Should be taken into consideration with other clinical findings and view of measurement on the ultrasound

What changes in the adrenal size and shape would we expect with:

1. pituitary-dependent HAC
   benign adrenal-dependent HAC?

2. malignant adrenal-dependent HAC?

3. both pituitary and adrenal dependent HAC?

1. bilaterally enalrged

2. unilaterally enlarged

3. unilateral adrenal enlargement, potential atrophy of the other adrenal

4. adrenal asymmetry without it being as extreme (very rare and difficult to diagnose)

In addition to hyperadrenocorticism, what other pathological processes can cause adrenomeglay?

• chronic stress

• chronic stress on non-adrenal illness

• phaeochromocytoma

• non-cortisol secreting adrenocortical tumours

• rare things like metastatic tumours, tuberculosis or other granulomatous lesions, congenital adrenal hyperplasia.

For obese cats:

1. what is the ideal body score for a cat

2. what are the two types of body condition scores

3. why is it relevant to know which type we’re using

4. why is it an advantage to use BCS rather than simply weight??

1. 5/9 - 44-55% body fat (each level is around 5% body weight0

2. body and muscle condition scores

3. an animal may have lots of fat storage but no muscle

4. looks at composition rather than mass (see point above), but it is subjective (weight is objective and comparable). should take both in every clinical scenario.

Obesity can be detrimental to many different body systems. Which systems are at risk and what are possible consequences of obesity to these body systems.

1. heart, CVS

2. liver

3. increased pressure on joints

4. increased inflammatory markers

5. endocrine - stored cells with fat → hormone synthesis and storage is limited/suppressed.

What are the physiological principles behind weight gain in the following endocrine diseases?

1. hyperadrenocorticism

2. hypothyroidism

3. acromegaly

1. more glucose → more insulin → more storage

2. decreased T3/T4 → decreased metabolic rate → less food needed → starvation response → storage

3. increased growth hormone

Outline how a glucose-intolerance test is take

Prep: fast the cat for 12 hours

1. take a blood sample - 0.5ml into FOx

2. either via IV (500mg/kg) or orally (2g/kg), give the glucose solution

3. take samples into FOx tubes after 5, 10, 15, 30, 45 nd 60 minutes

4. send to a lab

5. observe results

In a glucose-tolerance test what would we expect for:

1. normal cat

• plasma glucose initially rises and falls off, to return to normal values within 2-3 hours

  • half life of glucose = 16-38 minutes

In a glucose-tolerance test what would we expect for:

1. diabetic cat

1. reduced first phase of insulin secretion, followed by a delayed, exaggerated insulin response

In a glucose-tolerance test what would we expect for:

1. glucose intolerance

2. what may this be caused by?

1. second phase of insulin secretion is lost → glucose levels stay higher longer

2. diabetes mellitus, phaeochromocytoma, hyperadrenocorticism

In a glucose-tolerance test what would we expect for:

• islet cell functional tumour

• lower maximum plasma glucose levels and more rapid return to pre-glucose levels

What do all steroid hormones begin as?

• cholesterol

What is the pathway of steroid hormone production

• cholesterol → pregnenolone

What is cholesterol conversion into pregnenolone limited by?

• ACTH

What is ACTH synthesised from?

• POMC

How does HAC differ between horses and dogs?

• dogs is caused by an excess of HAC

• horses - caused by the zona intermedia in the pituitary gland → more hormones involved (blue circle)

Outline the physiology of glucocorticoids

• how are they transported in blood

• how do they signal at their target cell

1. 90% bound to plasma proteins

2. bind to specific cell membrane/cytosolic receptor at target → transported to the nucleus → altered gene expression

What are 4 actions of glucocorticoids

1. stimulates gluconeogenesis

2. stimulates glycogenolysis

3. causes proteolysis

4. promotes lipolysis

Outline the effect of glucocorticoids on:

1. fat

2. muscle

3. liver

1. mobilisation from peripheral stores

2. catabolism

3. gluconeogenesis, antagonise insulin

Outline the effect of glucocorticoids on:

1. kidney

2. skin

3. bone

1. increased GFR, blocked ADH action

2. follicular atrophy, sebaceous gland atrophy

3. reduce calcium levels, osteopaenia

Outline the effect of glucocorticoids on:

1. brain

2. immune system

1. hunger and thirst

2. release neutrophils from their marginal pool, down-regulates immune responses (T-cell function and recruitment, B-cell activation)

What is the main stimulus for aldosterone release?

• low blood pressure - RAAS

• high serum K+ also stimulates release

What are the 4 most important androgens?

1. testosterone

2. dihydrotestosterone (DHT)

3. dehydroepiandrosterone (DHEA)

4. androstenedione

What is the function of androgens?

• stimulate/control the development and maintenance of male characteristics by binding to androgen receptors

What are androgens the precursors for?

• oestrogens

What is HAC characterised by?

• excessive production of steroid hormones, especially glucocorticoids, from the adrenal cortex

Canine HAC:
1. how can is develop?

2. of one type, what are the two sub-types?

1. spontaneous or iatrogenic

2. PDH (90% of cases) or ADH

How does a PDH result in HAC?

• excess ACTH secretion → bilateral adrenal hyperplasia

How does ADH result in HAC?

• 50% adenomas

• 50% carcinomas

• independent of pituitary control - low ACTH

what is the difference in PD HAC:

1. microadenoma

2. macroadenoma

3. what effect do these have?

1. <10mm, majority of cases

2. >10mm, slow growing → neurological signs

3. normal negative feedback mechanisms fail

for AD HAC:

1. observation grossly of adrenal glands?

2. independent from…

3. calcification?

1. unilateral adrenal enlargement → atrophy of the contralateral side

2. ACTH control - conc low/undetectable

3. 50% of adrenal glands will be calcified regardless of tumour type

What tends to be the signalment of AD HAC?

• older dogs (11-12 years)

• larger breed dogs

What tends to be the signalment for PD HAC?

• middle aged dogs 7-9 years

• poodles, daschunds and small terriers

What are specific clinical signs that signal HAC?

• PU/PD

• abdominal enlargement (Pot belly)

• polyphagic (alopecia)

• skin changes

• hepatomegaly

• muscle wasting/weakness

• lethargy/exercise intolerance/panting

• reproductive changes

Apart from the known clinical signs:

1. how do most cases present

2. what organs are at risk

1. usually insidious (‘‘just ageing’’) - signs may be intermittent

2. liver, muscle, bone, kidneys, immune system, reproductive system, skin, respiratory system, CVS, CNS, PNS

Outline PU/PD in HAC

• PD: >100ml/kg/day dog, >50ml/kg/day cat

• PU: >50ml/kg/day

• PD secondary to PU

Outline abdominal enlargement seen with HAC

• classic ‘‘pot-bellied’’ appearance

• re-distribution of fat into adbomen

• hepatic enlagement

• wasting and weakness of abdominal muscles

• palpation may be easier

Outline polyphagia in relation to HAC

• assumed to be due to glucocorticoids

• may be misinterpreted

Outline cause of muscle wasting with HAC

• usually gradual

• caused by protein catabolism

With hyperadrenocorticism, where will we notice muscle wasting

• limbs

• spine

• temporal region

What skin changes may we see associated with skin changes

1. bilaterally symmetrical alopecia - inhibitory effects of steroids on anogen phase

2. thin skin and reduced elasticity - prominent abdominal veins

3. excessive scale and comedones

4. slow wound healing

with HAC why do we see:

1. thin skin and reduced elasticity w. prominent abdominal veins

2. slow wound healing?

1. protein catabolism (atrophic collagen) and loss of subcutaneous fat

2. inhibition of fibroblast proliferation and collagen synthesis

What is calcinosis cutis, wtih what endocrine disorder do we see it, where will we see it on an animal?

1. slightly elevated plaques surrounded by erythema

2. neck, axilla, ventral abdomen and inguinal areas

How can we treat HAC in the UK?

• trilostane (Vetoryl) licensed treatment.

  • it’s a reversible inhibitor of 3-beta hydroxysteroid dehydrogenase enzyme (prevents cortisol being produced)

• adrenalectomy or hypophysectomy → needs replaceent therapy for hormones

what is a US treatment method

• mititane (Lysodren) - chemical ablation of adrenal cortex, medulla spared

  • needs hormone replacement therapy

For HAC in cats:

• more/less common, why?

• uncommon, cats are more resistant to the effects of glucocorticoids

What is the signalment and are the major clinical signs of HAC in felines?

• middle-older age

• PU/PD, polyphagia, weight loss

• extreme skin fragility

• pendulous abdomen

• UTIs

What is the ratio of feline PD HAD: AD HAC

• 75-90% PD HAC

• 20-25% AD HAC

What can impact our results whilst testing for HAC?

• chronic illness

• psychological stress

What are the 4 investigations in to determining whether an animal has HAC?

• blood test investigation - biochem and CBC

• urinalysis

• imaging

• specific tests

What parameters do we measure in biochemistry for HAC? What do we expect?

1. ALP - in >90% cases

2. ALT (mild-moderate)

3. cholesterol

4. bile acids (mild-moderate)

5. fasting glucose

Reduced:

• BUN (blood urea nitrogen)

What haematological results do we expect with CBC for HAC?

1. neutrophilia

2. lymphopenia

3. eosinopaenia

4. monocytosis

What do we expect in urinalysis for HAC?

• low USG - often <1.015, can be hyposthenuric (<1.008)

• evidence of UTI

What abdominal radiographic findings do we expect?

1. hepatomegaly

2. pot-bellied appearance

3. calcinosis cutis

4. distended bladder

5. adrenal enlargement/calcification

What thoracic radiographic findings do we expect for HAC?

• tracheal and bronchial wall mineralisation

• pulmonary metastasis

• osteoporosis (more human)

What is the approximate normal size of an adrenal gland - ultrasound?

• 25mm x 5mm

What screening tests could we use for HAC?

1. urinary cortisol: creatinine ratio

2. ACTH stimulation test

3. low dose dezamethason suppression test (LDDS)

Outline the urinary cortisol to creatinine ratio:

1. ease of test?

2. when do we take a sample

3. sensitivity vs specificity?

4. expected ratio?

1. very easy

2. owner, in the morning

3. low ratio = HAC unlikely = highly sensitive

• high ratio = animals could have HAC but also elevated for many others = low specificity

What is the protocol for ACTH stimulation test

1. starve overnight

2. test plasma cortisol at time 0

3. inject synthetic ACTH

4. test plasma cortisol 60min later

For a dog with spontaneous HAC what would we expect when performing an ACTH stimulation test

• exaggerated response of cortisol increase

For the ACTH stimulation test:

1. easy, cheap?

2. sensitivity vs specificity?

1. quick, easy but expensive

2. okay sensitivity (85% PDH, >50% ADH) - don’t exclude if negative

3. best specificity of HAC (few false positives)

Outline the LDDS test protocol

1. starve overnight, measure baseline plasma cortisol, inject 0.01mg/kg dexamethasone IV

2. measure cortisol at 3 vs 8 hours

Of the LDDS test, what is a confirmatory result?

• >50nmol/L at 8 hours

What is the LDDS sensitivity vs specificity

• more sensitive - should detect nearly 90-95% of PDH and most ADH

• lower specificity (more false positives)

If the ACTH is negative BUT we’re suspicious of disease, perform what test?

• LDDS

  • negative - consider other diseases

  • positive - treat

what are the 4 tests we perform to differentiate ADH from PDH

1. (HDDS)

2. endogenous ACTH

3. adrenal imaging

4. pituitary imaging

what is the HDDS?

• same protocal as for LDDS, just 0.1mg/kg dexamethasone

How does HDDS, in theory differentiate b/w AD and PD HAC

PDH: - suppression of ACTH → decreased cortisol production

ADH: suppressing ACTH has no effect → continuously high cortisol levels

why are HDDS tests no longer used?

• 25-30% PDH tumours → ACTH has no effect on, so act as an AD HAC = high cortisol

For the endogenous ACTH:

1. what happens to the levels in a functional pituitary tumour

2. functional adrenal tumour

3. is it used to diagnose ADH or PDH?

1. increase, they’re high

2. stay low - negative feedback mechanism doesn’t work

3. ADH, PDH can fall within normal range

In adrenal imaging:

1. what does PDH look like

2. ADH?

1. symmetrical enlargement and normal conformation

2. one enlarged gland and one atrophied gland

With adrenal dependent HAC, why is one gland atrophied?

• negative feedback loop is functional in one gland, not the other.

• The gland producing excessive cortisol → negative feedback mechanism which the contralateral gland responds to → not used → atrophies

What can we use for imaging the pituitary?

• CT

• MRI

• expensive!!!

What affect do glucocorticoids have on the body? what is it controlled by?

1. gluconeogenesis

2. glycogenolysis

3. proteolysis

4. lipolysis

Controlled by ACTH

Outline aldosterone:

1. what does it play a central role in

2. where does it act

3. what does it cause

4. other than BP what can stimulate its release?

1. regulation of BP through RAAS

2. distal tubule and collecting duct

3. increases reabsorption of Na, Cl and hence water. Stimulates K+ release into tubular lumen.

4. high serum K+

How is renin release stimulated?

• baroreceptors in the wall of the afferent arteriole

• cells of macula densa in the distal tubule are stimulated by reduced NaCl delivery

• also baroreceptors in the cardiac and arterial

what are the 3 classifications of hypoadrenocorticism

1. primary → addison’s disease, loss of adrenal cortex

2. secondary → ACTH deficiency, rare

3. iatrogenic hypoadrenocorticism → exogenous steroids

Primary HypoAC:

1. known name

2. what is it

3. what does it occur with

4. what are some causes in dogs

1. addison’s disease

2. deficiency of glucocorticoids and deficiency of mineralocorticoids

3. idiopathic atrophy: maybe immune-mediated destruction

• iatrogenic

what are 2 drugs and a surgery that can result in primary hypoAC

Drugs: mitotane, trilostane

surgery: bilateral adrenalectomy

outline iatrogenic hypoAC:

1. cause

2. what may symptoms appear as?

3. how should we always remove steroids?

1. exogenous steroids → adrenal atrophy. affects cortisol only

2. signs of Cushing’s syndrome

3. taper off, suddenly remove → animal can crash

Outline the signalment of Addison’s

• young-middle aged dogs

• certain breed dispositions

• extremely rare in cats

Give 3 dog breeds predisoposed to addison’s

• standard poodles

• bearded collies

• portugese water dog

• leonberger

• great dane

• rottweiler

• WHWT

• soft coated wheaten terrier

Outline pathophysiology

1. aldosterone deficiency → loss of Na+, Cl-, H20, K+, H+ retention, pre-renal renal failure due hypovolaemia

2. glucocorticoid deficiency → decreased stress tolerance, GI signs, weakness, appetite loss, anaemis, impaired gluconeogenesis

what is addisionian crisis?

• acute HypoAC

• marked hypovolaemia with azotaemia

Outline the signalment of chronic HypoAC

• vauge and non-specific signs - wax and wane with treatment and stress

• anorexia, vomiting, diarrhoea, PU/PD, weakness, lethargy and depression

• appear normal b/w bouts, especially after some fluid therapy/steroid but RELAPSE

Outline the clinical signs of acute HypoAC

• history of V+/D+

• signs caused by hypovolaemic shock

• usually collapsed/v weak

• paradox of relative bradycardia

• some abdominal pain (seems like pancreatitis)

why do we get bradycardia with acute Addisonian shock?

• hyperkalaemia