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ACVIM Generals Revision > Endocrine Clinical > Flashcards

Endocrine Clinical Flashcards

1
Q

Possible reasons why congenital hyposomatotropism may occur?

A

Failure of Rathke’s pouch development (LHX3 mutation)

Hydrocephalus

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2
Q

When might congenital dwarfism be noted?

A

after 1-2 months, this is the period in which growth is more dependent on genetics.

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3
Q

Clinical features of congenital hyposomatotropism

A 
Retained deciduous teeth
Dull and dry hair coats
Corneal oedema
Weakness and lethargy
Proportionate dwarfism
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4
Q

What conditions could falsely decrease IGF-1?

A 
Liver disease
Lymphoma
Diabetes (newly diagnosed)
Renal disease
Body size
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5
Q

What is the pathophysiology of iatrogenic hypothyroidism?

A

The elevated thyroid hormones suppress TSH and so once this negative feedback is removed and the overactive thyroid cells are gone all that is left is atrophied cells. It takes time for these to grow again and start secreting T4.

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6
Q

What type of genetic inheritance pattern does congenital hypothyroidism show?

A

Autosomal recessive.

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7
Q

How can you tell the difference between congenital dyshormonogenesis and dysmorphogenesis in hypothyroidism?

A

Dyshormonogenesis may result in a goitre as TSH is high and the gland enlarges as there are cells there.

Dysmorphogenesis will not cause gland enlargement as the cells are just not there.

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8
Q

Key features of feline congenital hypothyroidism

A

Constipation/Megacolon
Goitre (with dyshormonogenesis)
Delayed growth plate closure –>Disproportionate dwarfism
Mental dullness (thyroid is important for neurological development)

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9
Q

Key features of adult onset hypothyroidism (cats)

A

Dry, dull, unkempt coat
Lethargy
Inappetence

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10
Q

Which gland should you compare the thyroid to when performing scintigraphy in dogs vs. cats?

A

Dog: parotid
Cat: zygomatic

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11
Q

Which feline breed has thyroid dyshormonogenesis been noted in?

A

Abysinnian

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12
Q

What is the pathophysiologic mechanism behind congenital hypothyroidism caused by dyshormonogenesis?

A

It is a problem with thyroid peroxidase.

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13
Q

What are the roles of the following in thyroid scintigraphy?

  • Technetium
  • Iodine - 131
  • Iodine-123
  • Perchlorate
A
  • Tc = treated like iodine by the body so will be taken up by the thyroid gland
  • I-131 = used for treatment
  • I-123 = used for imaging
  • Perchlorate = Competes with Iodide for NIS transporter. Administration in dyshormonogenesis will cause discharge of iodide ions out of the gland as they are not bound to thyroglobulin.
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14
Q

What proportion of hyperthyroid cats have unilateral disease?

A

Likely <1/3. >50% of cases have bilateral disease but often it is asymmetrical.

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15
Q

What proportion of hyperthyroid cats have erythrocytosis?

A

50%.

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16
Q

What is the most common historical clinical sign in hyperthyroidism?

A

Weight loss - affecting 88% of cases.

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17
Q

What is the percentage of normal cats that have a goitre?

A

70%

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18
Q

What are the main effects of thyroid hormones on the heart?

A

Increase heart rate, up regulates beta receptors
Inotropy - alters ion channel activity and enhances myosin activity
Hypertrophy - increases expression of myocardial proteins.

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19
Q

Reasons why thyroid hormone may cause PU/PD

A

• Thyroid hormone may lead to increased GFR
○ Increases NO activity in the renal cortex
○ Increases beta-adrenergic receptors
○ Both may lead to activation of RAAS
○ Afferent arteriolar resistance will decrease and increased hydrostatic pressure lead to an increased GFR
• Thyroid hormone effects on tubular function
○ Upregulation of chloride channels –> enhanced chloride reabsorption
○ Decreased Cl delivery to the macula densa triggers tubuloglomerular feedback and increases GFR
○ Enhanced Na/K-ATPase activity + Na/H exchange –> increased Na/Ca exchange –> increased calcium reabsorption
§ Mild hypercalcaemia is noted in people with HT
§ Hypocalcaemia has been noted in FHT
• Thyroid directly impacts on creatinine physiology
○ Increases GFR
○ Enhances tubular secretion of creatinine
○ Muscle loss

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20
Q

What is true about fT4, does it have good sensitivity or specificity?

A

It has a good sensitivity as it is unlikely that a normal cat would have a high fT4. However, it is not very specific and non-thyroidal illness and result in it being in or out of the normal range very easily.

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21
Q

What might the reason for a high fT4 and low TT4 be?

A

This pattern can be seen in euthyroid sick syndrome.

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22
Q

When might T3 suppression and TRH stimulation tests be useful in diagnosing FHT?

A

T3 - when basal testing has failure to confirm. In a normal cat T3 will suppress thyroid hormone production

TRH - used to diagnose occult hyperthyroidism. In HT TRH will have minimal effect.

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23
Q

What thyroid to salivary ratio is diagnostic for FHT in thyroid scintigraphy?

A

> 1.5

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24
Q

What is the therapeutic target of T4 for treatment of feline hyperthyroidism?

A

Middle to lower half of the RI whilst controlling clinical signs.

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25
Q

What is the most common neuroendocrine tumour in a dog?

A

Thyroid carcinoma

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26
Q

Breed predisposition to thyroid carcinoma

A
  • Golden Retrievers
  • Boxers
  • Huskies
  • Malamutes
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27
Q

What proportion of dogs with thyroid carcinoma have clinical signs associated with over production of thyroid hormone?

A

<10%

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28
Q

Treatment options for invasive thyroid carcinoma

A

External beam radiation

I-131 - but this is not widely available due to the isolation facilities required for it.

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29
Q

Metastatic rate of insulinoma

A

45-64%

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30
Q

At what glucose level is insulin secretion inhibited in animals?

A

<4.4mmol/L (<80g.dL).

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31
Q

What are the most common sites of insulinoma metastasis?

A

Local lymph nodes and liver

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32
Q

What type of CT is required for optimal sensitivity for detection of insulinoma?

A

Dual phase - the arterial phase is required to show contrast enhancement.

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33
Q

Streptozocin

  • Indication
  • MoA
  • Side effects
A

Indication = insulinoma
MoA - selective destruction of neoplastic or metastatic beta cells
Side effects - main one is nephrotoxicity!!

34
Q

Diazoxide

  • Indication
  • MoA
  • Side effects
A

Indication = insulinoma
MoA = Possibly by preventing calcium release into the beta cell. Increases glycogenolysis, gluconeogenesis and inhibits tissue glucose uptake.
Side effects = gastrointestinal

35
Q

Renal threshold for glucose in dogs

A

10-12.2mmol/L (180-220mg/dL)

36
Q

Renal threshold for glucose in cats

A

14-16mmol/L (250-290mg/dL)

37
Q

What is the main problem with using fructosamine for diagnosing diabetes in cats?

A

It does not increase much if there is only a moderate elevation in blood glucose.

38
Q

What molecule has been added to lente insulin to allow it to have a longer duration of action?

A

Zinc

39
Q

Which breed has the highest odds of developing canine DM?

Which breed has the lowest odds of developing canine DM?

A

Highest = Australian terrier

Lowest = Boxers (negative risk)

40
Q

Which cat breeds are at increased risk of diabetes mellitus?

A

Burmese!!
Main coon
Russian blue
Siamese

41
Q

Oral hypoglycaemic MoAs

  • Sulfonylureas (e.g. glipizide)
  • Meglitinides (e.g. nateglinide)
  • Biguanides (e.g. metformin)
  • Thiazolidinedione
  • Alpha-glucosidase inhibitors (e.g. acarbose)
A
  • Sulfonylureas (e.g. glipizide): closes K+ channels and opens Ca channels in the insulin cells –> stored insulin release
  • Meglitinides (e.g. nateglinide): same as above
  • Biguanides (e.g. metformin): increase tissue insuli sensitivity and decrease gluconeogenesis (multiple mechanisms)
  • Thiazolidinedione: improves insulin sensitivity
  • Alpha-glucosidase inhibitors: inhibits brush border disaccharides in the SI
42
Q

What cytokines result in increased release of cortisol and why?

A

IL-1, IL-6 and TNF-a. These all result in increased hypothalamic release of CRH.

43
Q

Which enzyme is the zone glomerulosa lacking which means that it can only produce aldosterone?

A

17-alpha-hydroxylase.

44
Q

Which enzyme is required for conversion of 17-OH pregnenolone which allows the zona reticular to produce sex steroids?

A

17,20 lyase

45
Q

Which enzyme is responsible for production of oestradiole?

A

Aromatase

Aromatase can convert testosterone to estradiol and androstenedione to estrone.

46
Q

Which ocular disease is associated with canine hyperadrenocorticism?

A

Sudden acquired retinal detachment.

47
Q

What USG is expected in dogs with hyperadrenocorticism?

A

<1.020.

48
Q

What is the mechanism of action of trilostance?

A

inhibition of 3B-HSD (+/- some inhibition of 11BHSD).

49
Q

What cortisol level is considered a good range for trilostane treated animals (refers both to pre-pill and ACTH stimulation test).

A

40-151nmol/L (1.5-5.5ug/dL).

50
Q

Which area of the adrenal cortex is mitotane less likely to damage?

A

The zona glomerulosa => meaning aldosterone synthesis is more likely to remain intact.

51
Q

What progestagen has been associated with feline hyperadrenocorticism?

A

Megesterol acetate

52
Q

What percentage of cats with HAC have concurrent diabetes?

A

90%

53
Q

Why is the dose of dexmethasone different in dogs vs. cats for the diagnosis of HAC??

A

In cats, the dose is 0.1 (dogs 0.01mg/kg). This increases the specificity for HAC.

54
Q

What is the percentage reported for adrenocortical vs. adrenomedullary tumours?

A

75% cortical

25% medullary

55
Q

How is primary hyperaldosteronism distinguished from secondary hyperaldosteronism (e.g. due to CKD)?

A

Primary hyperaldosteronism will suppress plasma renin activity. Therefore, increased aldosterone along with decreased PRA are suggestive of primary hyperaldosteronism.

56
Q

What is the challenge in diagnosis of canine PHA?

A

There is no PRA assay available in dogs.

57
Q

Which sex steroid can mimic hyperadrenocorticism?

A

Progestagens.

58
Q

How are sex-homrone producing adrenal tumours diagnosed?

A

ACTH stimulation test pre and post sex steroid measurements. Oestrogen will not be affected.

59
Q

What is Zollinger-Ellison syndrome?

A

A symptom of gastrin excess characterised by:

  • Gastric astral hypertrophy
  • Hyperacidity
  • Ulceration
60
Q

What provocative tests may be useful in the diagnosis of gastrinomas?

A

Secretin stimulation
Calcium stimulation

Not all will respond but essentially a doubling of basal gastrin may be the cut off. Normal individuals should not produce more gastrin in response to these hormones.

61
Q

What is the main pathology seen in canine hypoadrenocorticism?

A

Lyphocytic-plasmacytic adrenalitis with cortical atrophy.

62
Q

Predisposed breeds to hypoA

A 
Leonburgers
Pomeranians
Great danes
Bearded collies
Standard Poodles
Springers
Portuguese water dogs
Cockers
WHWHT
Nova Scotia
63
Q

Atypical hypoadrenocorticism =

A

GC deficient but Na/K remains within normal limits (some may progress to MC deficiency with time).

64
Q

Breeds at decreased risk of hypoA

A

Golden Retrievers
Yorkshire Terriers
Pit-Bulls
Lhasa Apso

65
Q

How much tetracosactide should be given as a minimum in the ACTH stimulation test?

A

5mcg/kg

66
Q

How does calcium cause PU/PD?

A

Inhibits action of ADH

Prevents NaCl uptake in tubules

67
Q

Finasteride

  • Indications
  • MoA
A 
Indication = treatment of BPH in breeding animals as it does not inhibit testosterone. It will therefore mean that dogs remain fertile and maintain libido. 
MoA = 5a-reductase inhibitor. This hormone is normally responsible for converting testosterone to DHT in the prostate, liver and skin.
68
Q

Osaterone acetate

  • Indications
  • MoA
  • Side effects
  • Additional considerations
A

Indication = BPD.

MoA = multiple anti-androgenic mechanisms

  • Decrease testosterone transport into the prostate
  • Inhibits 5a reductase
  • Inhibition of prostate androgen receptors
  • Decreases nuclear androgen receptors

Side effect = increased appetite

It can affect adrenal function (and testing) as one of its metabolites can cause adrenal suppression through interaction with the glucocorticoid receptor.

69
Q

Megesterol acetate

  • Indications
  • MoA
  • Side effects
A

Indications: BPH, oestrus postponement,

MoA: synthetic progestin

Side effects:

  • Profound adrenocortical suppression can be found in cats.
  • Many, e.g. DM, acromegaly, mammary development, neoplasia etc.
70
Q

Medroxyprogesterone acetate

  • Indications
  • MoA
  • Side effects
A

Indications = BPH amoungst others
MoA = synthetic progestin
- Side effects = many.

71
Q

Deslorelin

  • Indications
  • MoA
  • Side effects
A

Can be used for BPH although it can’t actually be used in the US for this

MoA = GnRH analogue. The sustained release leads to down-regulation of GnRH receptors which reduces ovarian and testicular function

72
Q

How much more potent is T3 than T4?

A

3-5x

73
Q

What are the main thyroid pathologies implicated in primary canine hypothyroidism?

A

Lymphocytic thyroiditis

Idiopathic thyroid atrophy

74
Q

How much of the thyroid gland needs to be lost before clinical hypothyroidism will develop?

A

> 75%

75
Q

What percentage of euthyroid TGAA positive dogs will develop clinical hypothyroidism?

A

5%

76
Q

What are the most common signs of hypothyroidism in dogs|?

A

Lethargy
Obesity and weight gain
exercise intolerance
Dermatologic changes

77
Q

What is myxoedema caused by?

A

Accumulation of hyaluronic acid.

78
Q

Radiographic signs of congenital hypothyroidism?

A

Delayed growth plate closure

Epiphyseal dysgenesis

79
Q

Which thyroid hormone measurement is often most affected by the presence of TGAA?

A

T3

80
Q

Most common clinical signs of canine hyperparathyroidism

A

The most common clinical signs of hyperparathyroidism, in descending order, are polyuria and polydipsia, lethargy, weakness, hyporexia, and lower urinary tract signs related to calcium-oxalate urolithiasis

ACVIM Generals Revision (32 decks)

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