Thyroid Disorders 1

Question 1

How have clinical signs changed over time?

Answer 1

> 1990
- older cats, wt loss
- markedly increased appetite 
- ^ feacal volume 
- PD
- hyperactive and aggressive 
- overt CV dz (tachycardia, murmur, gallops, volume overload) 
- palpable thyroid nodule 
> 2009
- mainly older cats but average 10 (can be younger)
- wt loss,variable appetite (can be normal but most common presenting complaint is weight loss despite good appetite) 
- PD much more variable (

Question 2

How is hyperthyroidism associated with CV dz?

Answer 2

• hyperthyroidism -> ^ catecholamine sensitivity
• tachycardia and tachydysrhymthimas
• murmur over sternum
• gallop diastolic d/t impaired relaxation
• heart failure
• tachypnoea and panting
• decreased respiratory reserves
• DECREASED systemic vascular resistance (not PDF hypertension [CF COMMON KNOWLEDGE])

Question 3

Outline Pathogenesis of hyperthyroidism and cardiac problems

Answer 3

* ^ triiodothyronine T3*
> ^ tissue thermogenesis 
> v systemic vascular resistance 
- v effective arterial filling volume 
- ^ renal sodium resorption 
- ^ blood volume 
> ^ Cardiac inotropy and chronotropy 
- ^ CO 
- myocardial damage

Question 4

How can cardiac function be objectively assessed on echo?

Answer 4

Left atrium : aorta ratio

Question 5

Are all hyperthyroid cats with tachypnoea in heart failure?

Answer 5

NO, exertional dyspnoea also contributes

Question 6

Are endocrine problems presented as 1* endocrine in system analysis?

Answer 6

NO RARELY EVER

- except with Malutilisation

Question 7

What does hypertension in cats cause?

Answer 7

Retinal haemorrhage and detachment

Question 8

Is retinopathy common in hyperthyroid cats?

Answer 8

No BECAUSE HYPERTENSION NOT COMMON IN HYPERTHYROID CATS!!!
- though potential confounding factors
- hyperthyroid cats are irritable and nervous -> white coat hypertension
- transport cortisolaemia
> but chronic blood pressure rarely high

Question 9

How may hypertension change when Tx hyperthyroid ? How does this affect monitoring?

Answer 9

• may present their hypertension signs when hyperthyroidism controlled
• hypertension MORE common when NOT hyperthyroid
  > monitor blood pressure

Question 10

Clin path with hyperthyroidism

Answer 10

• ^ ALT 90% cases
• ^ ALP 45% cases (cats excrete very effectively, V SENSE, ^ SPEC, opposite in dogs)
• ^ BA 59% cases
  > liver enzymes should normalise when hyperthyroidism Tx
• stress leucogram
• physiological neutrophilia of all WBCs (esp if cat is a jerk)
• azotaemia ( see more info later)

Question 11

How can dx of hyperthyroidism be confirmed ?

Answer 11

> basal total T4
- high specificity (few false +) low sensitivity (false -)
basal free T4 ($$$ false positives)
- must be by equilibrium dialysis
- increases sensitivity by 10%, decreases specificity by 30%
basal cTSH levels helpful
- excellent specificity, appalling sesntivity
- only for research
T3 suppression test
thyroid scintigraphy

Question 12

Prevalence of hyperthyroidism and risk factors?

Answer 12

• exclusively cat dz
• prevalence ^ over last 20y
• increasingly recognised in different parts of the world
• acquired and idiopathic (various chemicals correlated - wet food chronic tyrosine deficiency, fire retardant polychromated halogens?)
• adenomatous hyperplasia with autonomous growth capacity
  > cf. humans graves Ab stimulate TSH-R
• very UNCOMMON in purebreds (colour dilution -> less tyrosine needed [precursor for melanin and thyroid hormone]