27. Diseases of the thyroid gland in dogs and cats

Question 1

Main thyroid hormones

Answer 1

TRH - thyrotropin releasing hormone
TSH - thyroid stimulating hormone
T3 - triiodothyronine
T4 - thyroxine

Question 2

Effect of thyroid hormones

Answer 2

Regulation of catabolism (weight loss/gain)
Regulation of chronotrop (oheart rate)
Regulation of body temperature
Regulation of digestion (alters the speed)
Control of muscle contraction
Control of cell apoptosis & replacement

Question 3

is Canine Hypothyroidism congenital

Answer 3

Rarely
Usually acquired

Question 4

Primary Canine Hypothyroidism

Answer 4

Thyroid failure
Autoimmune destruction of thyroid gland
Decreased T4
Increased TSH

Question 5

Secondary Canine Hypothyroidism

Answer 5

Pituitary failure
TSH deficiency —> follicular atrophy
Due to extrathyroidal gland illness - SES, neoplasia
Decreased T4
Decreased TSH

Question 6

Tertiary Canine Hypothyroidism

Answer 6

Hypothalamus failure
Due to decreased TRH
Decreased T4
Decreased TSH

Question 7

Predisposed to Canine Hypothyroidism

Answer 7

Dogs > cats
Young/ middle aged
Larger
Retriever
Dobermann
Boxer
Dachshung
Poodle
Schnauzer

Question 8

Pathogenesis of Canine Hypothyroidism

Answer 8

Usually lymphocytic thyroiditis –> slow cellular metabolism –> decreased metabolic rate

Question 9

Clinical signs of Canine Hypothyroidism

Answer 9

• Exercise intolerance
• Lethargy
• Weight gain/obesity
• Arthropathy
• Skin thickening
• Anoestrous
• Hyperpigmentation
• ↓ Fertility
• Alopecia (rat tail)
• ↓ Libido
• Testicular atrophy
• Facial paralysis
• Facial expression changes
• Ataxia
• Vestibular signs
• Obstipation
• Megaoesophagus
• Bradycardia
• ↓ ECG amplitude
• Weak heartbeat
• Myxoedema

Question 10

Lab D of Canine Hypothyroidism

Answer 10

Anaemia
Lipaemia
Increased ; cholesterol
Decreased ; Thyroxine, TSH

Question 11

Diagnosis of Canine Hypothyroidism

Answer 11

Lab d
TRH / TSH stimulation test
Thyroid scintigraphy

Question 12

Treatment of Canine Hypothyroidism

Answer 12

L- thyroxine

Question 13

Acute myxoedema coma cases

Answer 13

IV thyroxine
IV steroids
Broad spec abx
Passive rewarming with blankets

Question 14

Canine Sick Euthyroid syndrome

Answer 14

Decreased T3
Decreased T4
with no thyroid involement

Question 15

Causes of Canine Sick Euthyroid syndrome

Answer 15

Cushing’s
Surgery
Addison’s
Anaesthesia
DM
T3/ T4 supressing drugs

Question 16

Congenital Hypothyroidism in young animals

Answer 16

Thyroid dysgenesis
enzyme deficiency — decreased hormone synthesis

Question 17

Acquired Hypothyroidism in young animals

Answer 17

iodine deficiency
Lymphhocytic thyroiditis

Question 18

Clinical signs of Hypothyroidism in neonates

Answer 18

Myxoedema
large fontanelle
suckling difficulties
goitre
hypothermia
hypoactivity

Question 19

Clinical signs of Hypothyroidism in later animals who had it as a younger animal

Answer 19

Disproportionate dwarfism
missing guard hairs
puffy facial features
goitre
large tongue
lethargy

Question 20

Diagnosis of Hypothyroidism in young animals

Answer 20

Thyroid function test
scintigraphy
granular structure of epiphysis on xray

Question 21

predisposed to Hyperthyroidism in cats

Answer 21

Middle/ old aged
mixed breed

Question 22

Causes of Hyperthyroidism in cats

Answer 22

Functional adenomatous hyperplasia –> gland enlargement
idiotpathic hyperplasia
adenoma
Increased T4
Decreased TSH

Question 23

Clinical signs of Hyperthyroidism in cats

Answer 23

• Polyphagia
• PU/PD
  Weight loss
• Nervousness
• Restlessness
• Panting
• Hyperactive aggressiveness
• Goitre
• ↑ Faecal volume
• Vomiting
• Sudden blindness
• Arrhythmia
• Systolic murmur
• Gallop rhythm
• Tachycardia → HF
• Diarrhoea
• Heat avoidance
• Hypertension
• Renal insufficiency
• Unkempt hair

Question 24

Diagnosis of Hyperthyroidism in cats

Answer 24

physical exam - tachycardia, hypertension
Lab d
Thyroid scintigraphy

Question 25

Lab d of Hyperthyroidism in cats

Answer 25

Increased; serum T4, PCV, ALT, ALP

Question 26

Treatment of Hyperthyroidism in cats

Answer 26

Radioactive iodine therapy - gold standard Iodine131 Surgery - thyroidectomy Carbimazole, methimazole - blocks thyroid hormone synthesis Low iodine diet

Question 27

Complications of treatment of Hyperthyroidism in cats

Answer 27

Decreaded T4 --> Decreased BP --> decreased GFR --> azotaemia

Question 28

Prognosis of Hyperthyroidism in cats

Answer 28

No renal failure ===> good prognosis renal failure ===> poor prognosis

Question 29

Predisposed to Thyroid tumours in dogs

Answer 29

Old boxers beagles retrivers

Question 30

What are Thyroid tumours in dogs most likely to be

Answer 30

Malignant unilateral non hormone producing

Question 31

Clinical signs of Thyroid tumours in dogs

Answer 31

Goitre --> dyspnoea, dysphagia Cough signs of hyperthyroidism

Question 32

Diagnosis of Thyroid tumours in dogs

Answer 32

xray FNA Increased T4

Question 33

Treatment of Thyroid tumours in dogs

Answer 33

Urgent thyroidectomy Iodine 131 if tumour is functional

Question 34

If you are performing a bilateral thyroidectomy, what should you do

Answer 34

Give L-thyroxine & cytostatic drugs after