28. Diseases of the thyroid gland in dogs and cats Flashcards
Main thyroid hormones and effect of thyroid hormones?
Canine hypothyroidism?
Canine Hypothyroidism
Congenital cases are rare
Acquired
Primary hypothyroidism (thyroid failure)
§ Autoimmune destruction of thyroid gland → Lymphocytic
thyroiditis
§ ↓ T4; ↑ TSH
Secondary hypothyroidism (pituitary failure)
§ TSH deficiency → Follicular atrophy
§ Cause: Extrathyroidal gland illness e.g neoplasia, systemic
illness, drug therapy and sick erythroid syndrome (SES)
§ ↓ T4; ↓ TSH
Tertiary hypothyroidism (hypothalamus failure)
§ Due to ↓ TRH
§ ↓ T4; ↓ TSH
Canine hypothyroidism predisposed, pathogenesis, clinical signs diagnosis and treatment?
Canine sick euthyroid syndrome?
Canine Sick Euthyroid Syndrome
↓ T3/↓ T4 with Ø thyroid involvement
Causes
§ Cushing’s § Surgery
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§ Addison’s § Anaesthesia
§ DM § T3/T 4-suppressing drugs
Hypothyroidism in young animals?
Hypothyroidism In Young Animals
CONGENITAL
§ Thyroid dysgenesis
§ Enzyme deficiency (peroxidase) → ↓ Hormone synthesis
ACQUIRED
§ Iodine deficiency (meat-only diet)
§ Lymphocytic thyroiditis
CLINICAL SIGNS
Neonates
§ Myxoedema § Goitre
§ Large fontanelle § Hypothermia
§ Suckling difficulties § Hypoactivity
Later life
§ Disproportionate dwarfism § Goitre
§ Missing guard hairs § Large tongue
§ Puffy facial features § Lethargy
DIAGNOSIS
§ Thyroid function test: TRH; TSH
§ Scintigraphy
§ Radiology: Granular structure of epiphysis
Hyperthyroidism in cats?
Hyperthyroidism in cats
PREDISPOSED
Middle/old-aged > Young cats; Mixed breed > Pure breed
PATHOGENESIS
Causes
§ Functional adenomatous hyperplasia → Gland enlargement
§ Idiopathic hyperplasia
§ Adenoma
May be bilateral/unilateral; ↑ T4 → ↓ TSH
CLINICAL SIGNS
§ 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
It is important to consider all conditions the animal may have, particularly focusing on the heart & kidneys
Physical exam
§ Tachycardia
§ Hypertension (due to myocardial hypertrophy)
Lab. D
§ Measure serum TT4: ↑ T4
§ ↑ PCV; Leucocytosis; Neutrophilia
§ ↑ ALT; ↑ ALP (without primary hepatic disease)
§ Azotaemia; Hyperglycaemia
Imaging: Thyroid scintigraphy
TREATMENT
§ Radioactive iodine therapy (IV) Gold standard (the cat will
§ however, be radioactive; Cat shouldn’t go home);
Iodine131
§ Surgery: Thyroidectomy; If bilateral – L-thyroxine needed
§ Blocking thyroid hormone synthesis – Carbimazole;
Methimazole
§ Low-iodine diet (not very palatable for cats, however)
Complication of treatment
↓ T4 → ↓ BP → ↓ GFR → ↑ Azotaemia
Ø Treatment → Thyroid storm
PROGNOSIS
✗ Renal failure → Good prognosis
✓ Renal failure → Poor prognosis
Thyroid tumours in dogs?
Thyroid Tumours In Dogs
Predisposed: Old boxers; Beagles; Retrievers
More likely to be malignant, unilateral & non-hormone-producing
CLINICAL SIGNS
§ Goitre → Dyspnoea; Dysphagia
§ Coughing
§ Signs of hyperthyroidism
DIAGNOSIS
§ Thoracic radiology
§ FNA; Biopsy
§ Lab. D: ↑ T4
TREATMENT
Thyroidectomy (urgent!)
§ If bilateral thyroidectomy – L-thyroxine & cytostatic drugs should be given after
Radiotherapy (if the tumour is functional)
§ Iodine131
