Hyperthyroidism

Question 1

What is hyperthyroidism?

Answer 1

• It is the excessive production of thyroxine (T4) and triiodothyroxine (T3)
• Primarily seen in middle to older cats
• Non-specific signs
• Can happen to dogs
• usually from thyroid carcinomas
• Decreased stress tolerance
• can lead to respiratory distress and cardiac arrest in cats
• Enlarged thyroid gland seen in 80% of cats
• Periods of excessive and decreased appetite
• Cardiac abnormalities are common (secondary complications)
• hypertrophic (reversible with tx of hyperT)
• dilated cardiomyopathy
• > 70% of glad damaged before signs show
• howl and pace

Question 2

Tx of hyperhyroidism?

Answer 2

• Surgical thyroidectomy
• Radioactive iodine
• Anti-thyroid drug
• Methimazole (Tapazole)
• Propylthiouracil (PTU)

Question 3

What ECG changes would you see in patients with hyperT?

Answer 3

• Sinus tachycardia
• Increased R wave amplitude
• Atrial premature complexes
• Left fasicular block
• VPCs
• Atrial tachycardia
• Ventricular tachycardia
• Incomplete atrioventricular block

Question 4

What are the tests needed to diagnose HyperT?

Answer 4

• T3 and T4 should be done (Free and total)
• No TSH assays available for cats and not trust worthy in dogs
• T3 suppression test can be used to confirm presence of HyperT in cats
• Obvious enlarged lobes (uni or bilateral) of thyroid gland

Question 5

What are the goals of tx of hyperT?

Answer 5

• To control excessive thyroid production
  1. Surgical thyroidectomy
• high mortality and morbidity rate
• hypoparathyroidism
• Horner’s syndrome
• laryngeal paralysis
• hypocalcemia is the most serious complication due to potential removal of all parathyroid gland tissue
• iatrogenic hypothyroidism
  2. Radioactive iodine
• irradiates hyperfunctioning cells and destroys them
• normal cells remain intact and minimally affected
• BEST tx option
  3. Medication
• Methimazole (Tapazole)
  
  • blocks use of iodine
  • inhibits further formation of thyroid hormones
  • no risk of causing hypothyroidism or hypoparathyroidism
  • disadvantage:
    - anorexia
    - Vomiting
    - lethargy
    - client compliance
    - hepatic toxicity
    - thrombocytopenia
    - severe leukopenia
    - IMHA
• PTU
  
  • contraindicated in cats due to adverse side effects