Hyperthyroidism physiology Flashcards

1
Q

What are the most common endocrinopathies seen in cats?

A

hyperthyroidism
diabetes mellitus

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2
Q

Describe the pathology of hyperthyroidism

A

Excessive T4 production
Adenomatous hyperplasia of thyroid glands - more functional cells in gland

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3
Q

Describe the pathophysiology of hyperthyroidism

A

Increased metabolic rate
Increases catabolism as uses up energy reserves
Effects thermoregulation
Effects interaction with CNS (increased sympathetic drive)
Effects emetic centre - makes animal feel nauseous

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4
Q

What are the clinical signs of hyperthyroidism

A

Weight loss
Polyphagia
PU/PD
Tachycardia
Diarrhoea
Resp abnormalities
vomiting
Haircoat changes (alopecia, matting, seborrhea, thin skin)

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5
Q

Why does hyperthyroidism cause weight loss and polyphagia?

A

Increased metabolic rate
Increased catabolism

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6
Q

Why does hyperthyroidism cause PU/PD

A

increase CO, GFR and medullary blood flow
Psychogenic component?

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7
Q

Why does hyperthyroidism cause vomiting?

A

overeating
activation of emetic centre

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8
Q

Why does hyperthyroidism cuase diarrhoea?

A

hypermotility
dietary indiscretion - eating odd things
Malabsorption due to excessive eating

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9
Q

What behavioural changes are associated with hyperthyroidism and what causes them?

A

Hyperactivity
Vocalisation
Agitation and restlessness
Obsessive grooming
Caused by:
- thermoregulation
- increased sympathetic drive

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10
Q

What would you on a clinical exam of a cat with hyperthyroidism?

A

thin
cervical nodule (goitre) - enlarged lymph node
Tachycardia
Systolic murmur
Dysrhythmias (premature contractions)

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11
Q

What causes hypertrophic cardiomyopathy in hyperthyroidism?

A

direct effect of thyroid hormones on myocytes
Indirect effect of adrenergic nervous system
Indirect compensatory changes for altered peripheral effusion

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12
Q

What can be seen in clinical chemistry of hyperthyroidism?

A

Alkaline phosphatase
ALT - some liver compromise due to metabolic effects
Mild Ca and P increase due to bone turnover

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13
Q

Describe methods of diagnosing hyperthyroidism

A

Baseline hormone conc:
- Total T4
- Free T4
Dynamic hormone tests:
- T3 suppression test
- TRH stim test
Scintigraphy

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14
Q

What are the limitation of total T4 measurement in diagnosing hyperthyroidism?

A

normal fluctuations
may be normal in early or mild hyperthyroidism
Depressed by non-thyroidal illness

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15
Q

Describe the T3 suppression test in hyperthyroidism diagnosis

A

In normal cats exogenous T3 => decrease in TSH and T4
Hyperthyroid cats:
- minimal decrease in T4
Used to rule out hyperthyroidism (screening test)

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16
Q

Describe thyroid scintigraphy in hyperthyroidism diagnosis

A

Radioactive marker identifies functional thyroid tissue
Density of thyroid glands can be compared
Used to confirm hyperthyroidism
Determines benign vs malignant disease
Identifies metastatic disease

17
Q

What are the treatment options for hyperthyroidism?

A

Medical - inhibitors of thyroid hormone synthesis
Surgical - remove enlarged thyroid glands
Radiotherapy
Dietary control - iodine and selenium deficient

18
Q

Why is surgical removal of thyroid glands difficult

A

Closely associated with parathyroid glands
Hypocalcaemia if removed

19
Q

Describe canine hyperthyroidism

A

rare
thyroid carcinomas
highly metastatic