Trevor battles hyperthyroidism

Fourteen year old Trevor had been behaving a bit unusual lately. His owners had noticed that he was no longer cleaning his coat and had matted fur around the base of his tail. He was also eating a lot of food and never quite seemed to get full, always pestering his owners at meal times with his new, very loud "yowling". He was starting to feel a bit lighter and bonier than he had been previously. Trevor's mum decided to book in for a senior consultation with one of our veterinarians to get him checked over.

On presentation, it was found that Trevor had indeed lost some weight since his last weigh in 6 months ago. He had lost a significant 900 grams, which is a lot considering he used to be 5.9 kg, thus meaning he had lost 15% of his body weight. His blood pressure was 240mm Hg. A normal blood pressure for a cat is 160-180mm Hg and with a distressed cat visiting the vets can reach about 200mm Hg. Trevor's heart rate was also extremely fast, beating at 250 bpm which is rapid, even for an anxious cat. Trevor also had a small lump in his neck at the location of his thyroid gland. The rest of his clinical examination was essentially normal.

Our veterinarian suspected that Trevor might have a condition called hyperthyroidism, which is when the thyroid gland produces an excessive amount of the thyroid hormone. The thyroid hormone is associated with the metabolism of the body so a high level of it results in everything in the body working overtime. The main complication arises due to the resulting high blood pressure, which damages the fine blood vessels in the kidneys and in the retina located at the back of the eye. Occasionally cats will present with advanced cases of hyperthyroidism with either their retinas detatched or their kidneys failing so the importance of detecting and treating early is paramount.

Trevor was started on some blood pressure medication to try and reduce any further damage. It is worth mentioning that once treatment for blood pressure and hyperthyroidism is commenced, it is necessary to recheck the concentration of the urine and the renal enzymes as renal failure can become apparent once the blood pressure is at a normal level (i.e the kidneys may be able to cope at the higher blood pressure level and sustain further damage, but may not be able to cope with a normal blood pressure).

A urine sample was collected from Trevor at the initial consultation to check the concentration of his urine, and thus determine how well the kidneys were functioning. The results did not show anything abnormal. A blood test was then collected to check Trevor's thyroid levels and renal enzymes. It was found that his thyroid hormone was very high and his renal enzymes were normal.

The options for treatment of hyperthyroidism were discussed once the results were known. There are four options, with the most common being neomercazole, which is a medication administered twice daily in most cases. More recently we have started using an ointment called methimazole that can be placed on the inside of a cat's ear and absorbed transdermally (across the skin). This is recommended for cats that are difficult to give tablets. Alternatively, once the blood pressure and the status of the kidneys are determined after commencing the above treatments, other options include surgical removal of the thyroid mass (generally a benign isolated growth) or radioactive iodine (administered at a referral facility).

Trevor's owners decided to start on the ointment. One month after starting the medication Trevor returned for a repeat check over, blood test and urine sample. He had gained 400grams, was eating a lot less and wasn't as vocal as he had been previously. His blood pressure had returned to normal, his urine sample showed that his kidneys were still functioning well, a blood test showed that his thyroid level was in the normal range and his kidney enzymes were normal too. Keep it up Trevor!