Feline Hyperthyroidism – the case of the ‘hangry’ cat

Feline hyperthyroidism is the most common endocrine disorder in older cats and is caused by overactive thyroid glands which are located in the neck. Most cases are the result of a benign change to one or both the glands called ‘hyperplasia’ or ‘ademona’. The excess thyroid hormone has a profound effect on metabolism, and this stresses the heart, digestive tract, kidneys, and many other organs. Once diagnosed, your cat should receive some form of treatment – when left untreated, clinical signs will progress leading to severe weight loss and lifethreatening complications.

The following signs should alert you that your cat possibly has hyperthyroidism:

• Losing weight despite having a normal, and most often, increased appetite

• Restlessness and agitation – at times resulting in increased vocalisation and even increase in cat fights

• Increased drinking and urinating

• Poor hair coat, unkept fur

• Rarely, lack of appetite and lethargy

Diagnoses:

During your regular health checks, your veterinarian may discover increased breathing and heart rate, high blood pressure, an enlarged thyroid gland or weight/muscle loss. Usually, a quick in-house blood test will reveal elevation of the thyroid hormones confirming the diagnoses. Because other medical conditions can occur along with it, comprehensive screening is imperative.

Treatment options:

Four common treatments are available. The choice of treatments depends on numerous factors including the cat’s age and temperament, cost, availability, ease of administration, other disease conditions and your lifestyle.

Radio-iodine therapy

(nicknamed I-131): this is the gold standard option and consists of administering a small dose of radioactive iodine which only the overactive thyroid gland cells will absorb. The radiation then destroys the overactive cells while the normal thyroid cells continue to function. Even though this radiation exposure carries minimal risk to your cat and yourself, special facilities are required for treatment, and specific isolation protocols need to be adhered to for the first week or two after treatment.

Advantage: in most instances once off treatment is curative, there is no anesthesia or surgery, no ongoing medication or monitoring needed Disadvantage: few facilities provide this treatment and referral to specialised centers is often necessary

Medical therapy: anti-thyroid medications will block the excess production of thyroid hormone and control the disease. This option does not cure the disease and your cat will have to take life-long medication.

Advantages: readily available, low initial cost, no hospitalisation or surgery needed

Disadvantages: need for daily medication life long, potential adverse drug effects, ongoing monitoring, high long-term cost of treatment

Surgical treatment: surgical removal of the entire/part of the thyroid gland.

Advantages: can be curative and eliminate the need for long term medication

Disadvantages: general anaesthesia is needed – and not all cats are good candidates, varying complications of surgery may occur including nerve/ blood vessel damage, damage or accidental excision of the parathyroid glands, recurrence of the condition due to unrecognised tissue during surgery.

Nutritional therapy: this involves feeding a specialised diet with iodine restriction – iodine is needed to produce thyroid hormones, and as such will control the disease is some patients. Advantages: low initial cost, ease of treatment

Disadvantages: the cat is not allowed to eat anything else – which can be hard in a multi-cat household, hunting cats, outside cats eating at neighbour’s etc., high long-term cost due to ongoing monitoring, could refuse to eat the diet

Management goals:

The goal of therapy is to restore normal thyroid function and minimise side effects without lowering the thyroid levels to below normal (hypothyroidism). Regular health assessments are important – sometimes treating the hyperthyroidism can ‘unmask’ previously hidden conditions.

Tauranga Veterinary Services is proud to announce that we will soon be offering the worldwide gold standard radioactive iodine treatment in our clinic!