Feline hyperthyroidism
Cats onlyKey concepts ·Also called: overactive thyroid cat, hyperthyroid cat, thyrotoxicosis
What it is
Almost always caused by benign overgrowth of thyroid tissue, hyperthyroidism floods the body with thyroid hormone and drives the metabolism far too fast. Diagnosis rests on a raised total T4 together with the clinical signs, with free T4 and TSH added when the picture is borderline.
Why it matters
It is thoroughly treatable — with medication, a prescription diet, surgery, or radioactive iodine — and treated cats often do very well. The complication that catches owners out is the kidneys: the overactive thyroid pushes extra blood through them and masks existing kidney disease, which then becomes visible once treatment starts.
What it can point to
- Weight loss despite a good or increased appetite
- Increased thirst and urination, restlessness, or night-time yowling
- A raised total T4, usually with raised ALT and sometimes raised ALP
- High blood pressure, which can damage the eyes if left unchecked
- Kidney values that look reassuring before treatment and rise afterwards, revealing pre-existing kidney disease
Dogs and cats differ
This is a feline condition. Dogs almost never develop naturally overactive thyroids, and a raised T4 in a dog is far more likely to reflect over-supplementation than disease.
Questions worth asking your vet
- Which treatment option suits my cat's age and other health problems best?
- How will we monitor the kidneys once treatment starts?
- Has my cat's blood pressure been checked?
Related terms
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