Thyroid Disorders

Question 1

What are the clinical signs of hyperthyroidism?

Answer 1

Older cats
Weight loss with variable appetite
PD
Hyperactive/lethargy
Cardiac changes (Tachy +/- gallop rhythm and systolic murmurs)
Thyroid nodules

Question 2

Explain why hyperthyroidism causes cardiovascular disease…

Answer 2

Increased catecholamine sensitivity so tendency to develop tachycardia and tachydysrhythmias alongside a diastolic gallop rhythm due to impaired ventricular relaxation. Tachypnea and panting may also be present and there is decreased systemic vascular resistance.

Question 3

How does hyperthyroidism cause heart failure?

Answer 3

Increase in T3 leads to increased tissue thermogenesis, increased cardiac inotropy and chronotrophy and decreased systemic vascular resistance. Decreased systemic vascular resistance leads to a decreased in effective arterial filling volume and thus an increase in renal sodium reabsorption. This, along with the increased in cardiac inotropy and chronotrophy leads to decreased cardiac output (volume overload).

Question 4

What does hypertension cause in cats?

Answer 4

Retinal haemorrhage and detachment.

Question 5

What is the linked between hyperthyroidism and hypertension?

Answer 5

Hyperthyroid cats tend to be more stressier and as they are more sensitive to catecholamines you get a bigger response to small stresses.

Question 6

How can treating hyperthyroidism lead to hypertension?

Answer 6

Hyperthyroidism decreases vascular resistance so if treated vascular resistance will increase.

Question 7

What is seen on haematology and biochemistry of a hyperthyroid cat?

Answer 7

Elevated ALT and ALP
Elevated bile acids
Stress leukogram
Physiological neutrophillia
Urea higher than creatinine

Question 8

How do you diagnose hyperthyroidism?

Answer 8

Basal total T4
Basal free T4
T3 suppresion test
Scintigraphy

Question 9

How does hyperthyroidism affect GFR?

Answer 9

Increases GFR, hyperfiltration leads to glomerular sclerosis and eventually decreases GFR

Question 10

How can treatment of hyperthyroidism affect renal function?

Answer 10

Reduces GFR so the animal may become azotaemic.

Question 11

How would you treat hyperthyroidism in the cat?

Answer 11

Carbimazole
Methimazole
Unilateral or bilateral thyroidectomy
Thyroid irradiation

Question 12

Explain how carbimazole/methimzaole treats hyperthyroidism..

Answer 12

Blocks TH production

Question 13

Describe medical therapy guidelines for a hyperthyroid patient…

Answer 13

Carimazole at 10-15mg/day or methimazole at 2.5-5mg/day induction which lasts for 3 weeks.

Question 14

What are the adverse effects of medical treatment in a hyperthyroid patient?

Answer 14

GI signs: V/D, inappetence
Depression, lethargy
Facial pruritis
Anaemia

Question 15

What are the possible complications of thyroidectomies?

Answer 15

Hypocal

Recurrence of hyperthyroidism

Question 16

What dietary changes can be introduced to a hyperthyroid cat?

Answer 16

Diet with minimal iodine content e.g. hills y/d

Question 17

What species are associated with hypothyroidism? What causes it?

Answer 17

Dogs - congenital via enzyme deficiency of acquired by immune-mediated destruction of thyroid tissue.

Question 18

What are the clinical signs of hypothyroidism?

Answer 18

Lethargy
Overweight
Exercise intolerant
Alopecia, hyperpigmentation, thickened skin 
Infertility

Question 19

What would you expect on clinical pathology in a hypothyroid patient?

Answer 19

Mild non-regenerative anaemia
+/- elevated cholestero
+/- elevated CK
+/- proteinuria

Question 20

What is a DDx for hypothyroidism in young dogs? How are they differentiated and which breeds are predisposed to both?

Answer 20

Pituitary dwarfism.
Hypothyroidism will have abnormal calcification of long bones on radiographs
GSD predisposed.

Question 21

How is hypothyroidism diagnosed?

Answer 21

Combination of low basal total T4 and normal/elevated basal TSH.

Question 22

How is hypothyroidism treated?

Answer 22

Thyroxine tablets once daily