Common clinical signs include:
- Weight loss
- Polyphagia (excessive appetite)
- Tachycardia (fast heart rate)
- Cardiac murmur
- Polyuria/Polydipsia (excessive urination and drinking)
- Palpable goitre (enlarged thyroid)
Over 95% of affected cats have benign enlargement of the thyroid gland, affecting either both lobes (70% cases) or one lobe (30% cases) of the gland.
It is not known what causes enlargement of the gland. Medication is available to lower the levels of thyroid hormone which resolves the clinical signs.