27. Diseases of the thyroid gland in dogs and cats Flashcards
Main thyroid hormones
TRH - thyrotropin releasing hormone
TSH - thyroid stimulating hormone
T3 - triiodothyronine
T4 - thyroxine
Effect of thyroid hormones
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
is Canine Hypothyroidism congenital
Rarely
Usually acquired
Primary Canine Hypothyroidism
Thyroid failure
Autoimmune destruction of thyroid gland
Decreased T4
Increased TSH
Secondary Canine Hypothyroidism
Pituitary failure
TSH deficiency —> follicular atrophy
Due to extrathyroidal gland illness - SES, neoplasia
Decreased T4
Decreased TSH
Tertiary Canine Hypothyroidism
Hypothalamus failure
Due to decreased TRH
Decreased T4
Decreased TSH
Predisposed to Canine Hypothyroidism
Dogs > cats
Young/ middle aged
Larger
Retriever
Dobermann
Boxer
Dachshung
Poodle
Schnauzer
Pathogenesis of Canine Hypothyroidism
Usually lymphocytic thyroiditis –> slow cellular metabolism –> decreased metabolic rate
Clinical signs of Canine Hypothyroidism
- 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
Lab D of Canine Hypothyroidism
Anaemia
Lipaemia
Increased ; cholesterol
Decreased ; Thyroxine, TSH
Diagnosis of Canine Hypothyroidism
Lab d
TRH / TSH stimulation test
Thyroid scintigraphy
Treatment of Canine Hypothyroidism
L- thyroxine
Acute myxoedema coma cases
IV thyroxine
IV steroids
Broad spec abx
Passive rewarming with blankets
Canine Sick Euthyroid syndrome
Decreased T3
Decreased T4
with no thyroid involement
Causes of Canine Sick Euthyroid syndrome
Cushing’s
Surgery
Addison’s
Anaesthesia
DM
T3/ T4 supressing drugs
Congenital Hypothyroidism in young animals
Thyroid dysgenesis
enzyme deficiency — decreased hormone synthesis
Acquired Hypothyroidism in young animals
iodine deficiency
Lymphhocytic thyroiditis
Clinical signs of Hypothyroidism in neonates
Myxoedema
large fontanelle
suckling difficulties
goitre
hypothermia
hypoactivity
Clinical signs of Hypothyroidism in later animals who had it as a younger animal
Disproportionate dwarfism
missing guard hairs
puffy facial features
goitre
large tongue
lethargy
Diagnosis of Hypothyroidism in young animals
Thyroid function test
scintigraphy
granular structure of epiphysis on xray
predisposed to Hyperthyroidism in cats
Middle/ old aged
mixed breed
Causes of Hyperthyroidism in cats
Functional adenomatous hyperplasia –> gland enlargement
idiotpathic hyperplasia
adenoma
Increased T4
Decreased TSH
Clinical signs of Hyperthyroidism in cats
- 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
Diagnosis of Hyperthyroidism in cats
physical exam - tachycardia, hypertension
Lab d
Thyroid scintigraphy
Lab d of Hyperthyroidism in cats
Increased; serum T4, PCV, ALT, ALP
Treatment of Hyperthyroidism in cats
Radioactive iodine therapy - gold standard
Iodine131
Surgery - thyroidectomy
Carbimazole, methimazole - blocks thyroid hormone synthesis
Low iodine diet
Complications of treatment of Hyperthyroidism in cats
Decreaded T4 –> Decreased BP –> decreased GFR –> azotaemia
Prognosis of Hyperthyroidism in cats
No renal failure ===> good prognosis
renal failure ===> poor prognosis
Predisposed to Thyroid tumours in dogs
Old boxers
beagles
retrivers
What are Thyroid tumours in dogs most likely to be
Malignant
unilateral
non hormone producing
Clinical signs of Thyroid tumours in dogs
Goitre –> dyspnoea, dysphagia
Cough
signs of hyperthyroidism
Diagnosis of Thyroid tumours in dogs
xray
FNA
Increased T4
Treatment of Thyroid tumours in dogs
Urgent thyroidectomy
Iodine 131 if tumour is functional
If you are performing a bilateral thyroidectomy, what should you do
Give L-thyroxine & cytostatic drugs after