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Endocrine > Thyroid disorders 1 and 2 > Flashcards

Thyroid disorders 1 and 2 Flashcards

1
Q

CS - hyperthyroidism

A
  • mainly older cats but average age 10.2 years
  • wt loss with variable appetite
  • PD
  • hyperactive but can also be lethargic
  • cardiac changes (tachycardia +/- gallop rhythms, systolic murmurs)
  • thyroid nodule (70% cases)
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2
Q

Outline cardiovascular dz and hyperthyroidism

A
  • T4 increases in increased catecholamine sensitivity
  • tendency to develop tachycardia and tachydysrhythmias
  • diastolic gallop rhythms (impaired ventricular relaxation0
  • heart failure
  • tachypnoea and panting
  • DECREASED systemic vascular resistance
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3
Q

How does increased T3 in hyperthyroidism cause increased cardiac output?

A

Increased T3 –> increased tissue thermogenesis –> decreased systemic vascular resistance –> decreased effective arterial filling volume –> increased renal Na reabsorption –> increased blood volume –>increased cardiac inotropy and chronotropy –> increased CO

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4
Q

CS - hypertension in cats

A
  • retinal haemorrhage

- retinal detachment

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5
Q

What is the association b/w feline hyperthyroidism and hypertension

A
  • older studies suggest higher prevalence of hypertension in hyperthyroid cats
  • but retinopathy uncommon in hyperthyroidism
  • confounding factors (hyperthyroid cats = irritable, white coat syndrome and ‘transport’ hypercortisolaemia)
  • recent studies suggest 5% untreated hyperthyroid cats have hypertension > monitor BP (higher % if treated)
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6
Q

Clinical pathology - hyperthyroidism

A
  • increased ALT (88% cases)
  • increased ALP (45%)
  • increased bile acids (30-65%)
  • stress leukogram common
  • physiological neutophilia (v common in stressy cats)
  • azotaemia
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7
Q

How to confirm dx of hyperthyroidism

A

** basal total T4 ** (commonest method)
- basal free T4 (by equilibrium dialysis, increases sensitivity 10%, specificity by 30% but expensive)
- basal cTSH levels might be helpful (appalling sensitivity, excellent specificity, research purposes)
- T3 suppression tests
- thyroid scintigraphy
FOLLOW UP TESTING OPTIONS:
- elevated free T4 equilibrium dialysis
- alternatively repeat basal total T4 (6-8 wks later)
- tT4 > 35nmol/L and TSH

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8
Q

Outline the T3 suppression test

A
  • measure basal total T4
  • then 20microgm T3 per 12 hours for 7 doses
  • last dose > 2 hours before sample
  • tT4 should be
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9
Q

How common is intrathoracic hyperthyroid tissue?

A

10-12% cases

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10
Q

Outline azotaemia in hyperthyroidism

A
  • urea generally higher than creatinine
  • hyperthyroidism increases GFR, thus:
  • tx hyperthyroidism –> increased creatinine
  • remember an elevated creatinine is NOT clinically significant renal failure and that hyperfiltration results in glomerular scelorosis: progressive glomerular sclerosis will result in decreasing GFR
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11
Q

T/F: in hyperthyroid cats pre-tx azotaemia shortens MST

A

True

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12
Q

Discuss survival of hyperthyroid cats

A

non-azotaemic hyperthyroid (even if azotaemic after hyperthyroidism) then have good survival time. Exception is if you tx hyperthyroidism and make them hypOthyroid without correcting this as if these cats are azotaemic they will live for a shorter period of time.

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13
Q

Tx - hyperthyroidism

A
  • MEDICAL (carbimazole, methimazole)
  • UNILATERAL THYROIDECTOMY (sequential over 12-15 months, generally no replacement tx required)
  • BILATERAL THYROIDECTOMY (generally no replacment tx required)
  • THYROID IRRADIATION I 131
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14
Q

Outline medical tx of hyperthyroidism

A
  • carbimazole converted to methimazole (biologically active)
  • induction of carbimazole or methimazole
  • ‘induction’ lasts 2-3 weeks
  • if no effect then consider increasing the frequency or individual dose
  • once ‘controlled’ use a maintenance dose
  • expect side effects in 5-20% patients
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15
Q

Side effects - medical management of hyperthyroidism

A
  • GIT (inappetance, V, D0
  • depression, lethargy, general listlessness
  • facial pruritus
  • blood dyscrasias (anaemia, granulocytopaenia, thromboplasias)
  • minimal benefit in changing the thiolurea
  • invariably means medical management can’t be used, regardless of ROA
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16
Q

Describe sx tx of hyperthyroidism

A
  • unilateral thyroidectomy/ bilateral
  • 5% have recurrence of hyperthyroidism
  • most effective method
  • if doing unilateral sx, recommnedation is that some parathyroid is removed and placed in cervical tissue, hoping new BVs will develop so that parathyroid is not compromised at the bilateral sx, thus reducing risk of clinically significant hypoparathyroidism
17
Q

Describe iodine tx

A
  • dose b/w 110 and 183 MBq
  • > 97% efficacy
  • 2 week stay in hospital
  • MST is >6.5 years
  • off medications for at least 2 weeks prior to tx
  • Iodine 131
18
Q

Outline dietary tx of hyperthyroidism

A
  • minimal amounts of iodine to limit TH production
  • guidelines indicate exclusive use of diet so a controlled environment required
  • 80% success (controversial - hard to give a cat an exclusive diet)
  • not cheaper than methimazole/ carbimazole
19
Q

Describe hypothyroidism

A
  • DOGS!
  • less common than people believe
  • congenital abnormality or acquired disorder (more commonly)
  • CONGENITAL: enzyme deficiencies
  • ACQUIRED: I-M destruction of the thyroid tissue
  • almost never a problem because of problems with pituitary function
20
Q

CS - hyperthyroidism

A
  • lethargic, disinterested
  • may be overweight
  • can be exercise intolerant and have mm/joint pain
  • dermal changes of alopecia and hyperpigmentation with thickened skin
  • infertility (males and females)
  • occasionally neurological problems
21
Q

Clinical pathology - hypothyroidism

A
  • mild non-regenerative anaemia
  • elevated serum cholesterol (60%)
  • elevated serum CK (40%)
  • proteinuria (not uncommon)
  • remarkably non-specific!!!
22
Q

Diagnostics - hypothyroidism

A
  • *** basal total T4 with basal TSH **
  • basal free T4
  • TRH response test
  • TSH response test
  • thyroglobulin autoantibodies
23
Q

Why is there a diagnostic dilemma with hypothyroidism?

A
  • lots of things lower serum thyroxine levels:
  • hypothyroidism
  • hyperadrenocorticism
  • ANY illness where GC is increased (most dz)
    + no readily available biomarker for TH except TSH but cTSH not very specific nor sensitive and can’t be used alone
24
Q

Can you use thyroglobulin autoantibody to detect hypothyroidism?

A

No - not reliable enough as not all develop overt hypothyroidism and not all hypothyroid dogs have TGAA

25
Q

Can you use a therapeutic trial to diagnose hypothyroidism?

A

Difficulty in doing this is that it is hard to go back and measure thyroid (endogenous) levels at a later date. Thus certain dz (e.g. seasonal flank alopecia) can catch you out!

26
Q

What is the most specific test for hypothyroidism

A

basal total T4 (low) AND basal TSH (normal or increased) have 95% specificity if measured concurrently. Brackets indicate results positive for hypothyroidism

27
Q

T/F: basal total T4 can be normal in a dog with clinically overt hypothyroidism

A

True (on occasions)

28
Q

Tx - Hypothyroidism

A
  • thyroxine tablets, orally
  • dose variably recommended howvere generally: 20 microgm/kg, given once daily, BID occasionally recommended, some individuals suggest using post-tablet monitoring.
  • response within 3 weeks (otherwise wrong diagnosis!)
  • studies show 30% placebo effect with hypothyroidism tx!!
29
Q

Outline feline hyperthyroidism

A
  • almost exclusively feline
  • prevalence increasing
  • acquired and idiopathic although various chemicals incriminated (wet food, fire retardent chemical)

Endocrine (11 decks)

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