Hyperthyroidism (aka thyrotoxicosis) is the “hyper†working of the thyroid gland in producing more thyroid hormone (T3 and T4) than normal. The gland has two lobes, either or both of which might enlarge abnormally to cause this hyper activity. This enlargement is called thyroid adenoma or thyroid adenomatous goitre. This gland is located in the neck and the thyroid hormone has a vital role in the working of the body. It controls the rate of metabolism which subsequently monitors the overall activity level of the cat. Cats afflicted with this disease utilise their energy sooner than normal. It is a treatable disease and more common in middle-aged and old cats. The Siamese is said to be less prone to this disease compared to the other breeds although there is no solid, scientific proof. Hyperthyroidism is the most frequent of all endocrine system diseases.
Symptoms
The symptoms associated with hyperthyroidism are very severe. There is weight loss despite an increased appetite. There is also an increase in thirst, heart rate, bad temper, urination and overall activity of the cat. The cat stops self-grooming or overgrooms. Diarrhoea and puking is also observed. Heat can become more unbearable and the cat will always be found in cooler places. It will also be seen gasping for air when stressed out especially if the disease has developed into an advanced stage. Hair might shed in patches and they may also become more talkative. The degree of these symptoms may vary from cat to cat. It is also not necessary that all the symptoms stated start showing at the same time. Some cats in advances stages even lose their appetite, becoming generally lazy and weak.
Diagnosis
The vet will start with a complete physical examination and medical history of the cat. An enlargement of either lobe (the size of a pea) can be felt. At times, the tissue size increases towards the chest cavity or other unusual locations known as ectopic thyroid tissue which cannot be physically detected. A few blood tests will be performed hence. To dismiss the possibility of kidney problems, urine test must be performed; BP should be checked for hypertension and an electrocardiogram, chest X-ray and ultrasound if a heart disease is believed. Other tests include serum chemistry profile, T3 suppression test and radionuclide scans.
Sometimes, physical examination and symptoms point towards hyperthyroidism but the blood tests reveal the opposite. For this the test needs to be taken again or other tests must be taken to confirm the ailment e.g. technetium scan that along with diagnosing hyperthyroidism also detects the area where the gland has enlarged.
Causes
Mostly hyperthyroidism is caused by an enlargement of the thyroid tissue. This increase however, is not cancerous. The cause behind this increase in size has not been known as yet but cats are known to respond very well to the treatment
The other cause is the development of a cancerous tumour in the thyroid gland. It is also known as thyroid adenocarcinoma. It is the root cause of only 1-2% of cats afflicted with hyperthyroidism. The treatment in this case can be complicated.
Secondary Complications
Since the thyroid gland is responsible for the overall activity of the cat, it can affect all the organs of the body. Thyroid helps in increasing the heart beat and contraction of heart when needed. Hyperthyroidism can cause Left Ventricular Hypertrophy which is the enlargement of the left ventricle (also the largest) of the heart. This can cause heart attack and once hyperthyroidism is cured, this will also go away.
Hypertension caused by a high BP may further harm the eyes, kidneys, heart and brain if hyperthyroidism is not treated in time. Chronic renal failure although has no connection with hyperthyroidism, both can afflict in old age at the same time and be problematic. Increased supply of blood to the kidney because of hyperthyroidism can falsely indicate a normal or subtly changed kidney working. What is advisable here is that the treatment of hyperthyroidism be initiated with tablets and the function of thyroid gland and kidney observed via blood and urine tests. In some cases of successful treatment of the gland, the progress of the kidneys declines radically. This has to be handled by decreasing the dose so that the kidney function is also kept consistent and working.
Treatment
Firstly, there is drug therapy. The tablets control the amount of thyroid hormone produced and released. This is not a permanent solution and the medications are useful for a short period of time or have to be taken for a lifetime. Either methimazole, beta-adrenergic blockers or carbimazole is prescribed, both of which have no or minimal side-effects. An appetite loss, laziness and vomiting are usually the common side-effects witnessed in the first week. A reduction in White Blood Cells and platelets, liver diseases and skin irritation may also appear in rare cases and need separate treatment. Usually the concentration level of thyroid is controlled in about 20 days after which the doses are reset with respect to the response. Anti-thyroid drugs are easily available and cheap in short-term.
Hyperthyroidism can be permanently cured via surgical removal of the affected gland. It is also called surgical thyroidectomy and is usually successful unless there is ectopic thyroid tissue. Furthermore, even if it is successful, sometimes the healthy gland develops the disease at a later stage. If both lobes have to be removed, the parathyroid gland may be affected as well causing hypocalcemia and thyroid hormone supplement must be given to the cat for the rest of its life. there are also surgical and anaesthesia risks involved. Before surgery, the drug therapy must be introduced to normalise the concentration of thyroid and any heart problem must also be controlled. The surgery must be done by an experienced vet for there is danger of the parathyroid glands, closely located, being damaged.
Radioactive Iodine therapy (I 131) is the most effective treatment with a 95% success rate as a permanent solution irrespective of the location of the enlarged thyroid tissue. Radioactive iodine is administered via an injection to the cat. This is absorbed only by the abnormal tissue and is built up there. The radiations destroy this abnormal growth without damaging the parathyroid gland or any serious side-effects. For the owner and others who come in close contact to the cat, they need to be careful because of the radiations that the cat might emit for a while. The cat has to be hospitalised for around a month until the radiations emitted are reduced to an acceptable level. If the hormone concentration does not reduce, this procedure can be repeated. If there is also lack of self-grooming, laziness and weight gain, the cat’s diet may be supplemented with a tablet of thyroid hormone.
Licensed facilities in UK:
- Animal Health Trust (near New market)
- The university veterinary schools at Bristol, London and Glasgow
- Barton Veterinary Hospital, Canterbury
- Cardiff Cat Clinic
- Bishopton Veterinary Group, Ripon, North Yorkshire
In case of Thyroid Adenocarcinoma, radioactive iodine therapy is recommended with comparatively high doses of iodine administered.
Health and Care
The effectiveness of the medicines or any untoward reaction has to be kept in check via regular blood tests. Also, an old cat must be taken in for test of the thyroid area regularly even otherwise.
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