Hyperthyroid Cats

RADIOIODINE AVAILABILITY - UPDATE JUNE 2023

We are unfortunately unable to accept any new referrals for feline radioactive iodine treatment. In the last 18-months there have been issues with production and supply of radioiodine affecting human and veterinary hospitals alike. Our supplier has announced that they will stop production of injectable radioiodine at the end of June. At this time there are no alternative manufacturers or suppliers.  

A single injection of radio-active iodine is given into the scruff. This is taken up by the thyroid gland and selectively destroys the abnormal tissue. This treatment is generally seen as the gold standard treatment of hyperthyroidism.

Advantages

• Single treatment is curative in approximately 95% of cases
• No general anaesthetic is necessary, although mild reversible sedation is used
• All affected tissue is treated wherever it is located
• Very few side-effects
• Depending on the length of the treatment this can work out more economical than long-term medication or diet

Disadvantages

• Patients must remain hospitalised until radiation levels have dropped sufficiently usually 1- 2 weeks
• In a small number of cases it can take up to 6 months for the full effect to be seen (effective in most cases in 2 weeks)
• A small number of patients require a second injection
• Kidney disease can be unmasked if already present (as with all treatment options)

Surgical removal of the thyroid glands can cure hyperthyroidism. To minimise risks, a period of stabilisation with medication or dietary control prior to surgery is advised.

Advantages

• Curative if all affected tissue is removed
• Rapidly effective
• Short period of hospitalisation
• Widely available procedure

Disadvantages

• Requires a general anaesthetic
• Risk of damage to the adjacent parathyroid gland, which can result in low blood calcium levels and the requirement for short to long-term medication.
• In order to reduce the risk of calcium problems often only 1 of the 2 glands is removed. However, in 70% of the cases the remaining gland is affected and in these cases the condition recurs, requiring additional treatment months to years later.
• Only suitable when all affected tissue is accessible (up to 20% of affected cats have inaccessible tissue in their chest).

Daily administration of tablets or liquid medication control the condition by preventing over-production of the thyroid hormone.

Advantages

• Most cats are stabilised in under 4 weeks
• Anaesthesia and hospitalisation are not required
• The initial cost is lower than surgery or radio iodine

Disadvantages

• The condition is controlled, not cured, therefore lifelong treatment is required
• Some cats are difficult to give medication to, resulting in poor control
• Regular blood tests are necessary for monitoring
• Side effects occur in approximately 20% of cats, including skin irritation, liver changes, vomitting, suppression of white blood cells and anaemia
• The condition usually worsens over time, requiring dose increases
• Pregnant women must take precautions when handling medication

A gel version of the oral medication is available which is applied to the hairless side of the ear.

Advantages

• As per oral medication
• Easier than tableting in some cats
• Reduced risk of vomiting compared to tablets (other side effects are the same)

Disadvantages

• Not licenced in the UK
• As per oral medication
• Less reliable dosing compared to tablets
• Can irritate skin where it is applied
• Care must be taken to avoid absorption through human skin.

Hills y/d is a prescription diet with low iodine content. Iodine is essential for the production of thyroid hormone, so restriction prevents excess hormone production.

Advantages

• No requirement for anaesthetic or hospitalisation
• Easier to administer than tablets
• Initial cost lower than surgery or radio-iodine

Disadvantages

• The condition is controlled, not cured, therefore lifelong treatment is required
• To be effective it must be fed as the sole diet. Any alternative food or water could contain enough iodine to render the treatment ineffective
• Certain medications/supplements contain iodine and therefore prevent the treatment working
• Some cats may not find it to their taste
• Takes up to 12 weeks to take effect