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Hyperthyroidism in Cats


Hyperthyroidism in Cats

Postby admin » Sat Feb 27, 2016 11:15 pm

What is hyperthyroidism?
cat hyperthyroidism
Also known as "thyrotoxicosis", hyperthyroidism is an endocrine disorder that is caused by the overactivity of the thyroid gland, resulting in increased levels of thyroid hormones T4 and T3 being produced.
Most often, hyperthyroidism is caused by a benign tumour (called an adenoma) involving one or both of the thyroid lobes. Feline hyperthyroidism is the most common disease of the endocrine (hormonal) system.
Occasionally hyperthyroidism occurs as a result of the over administration of thyroid hormones when treating hypothyroidism (underactive thyroid gland).
What does the thyroid do?
Consisting of two lobes (left and right), the thyroid is located in the neck on either side of the windpipe. It produces two hormones T3 triiodothyronine and T4 thyroxine. Both hormones help control metabolism.
What are the symptoms of hyperthyroidism in cats?
The most common symptoms of hyperthyroidism in the cat include:
Weight loss despite an increased appetite
Increased thirst and urination
Behavioural changes (nervous/jittery behaviour, aggression, over-grooming and or bald patches, hyperactive, increased vocalisation)
Rapid heartbeat
Poor coat condition (see photos)
Weakness (occasionally)
Decreased appetite (occasionally)
Hypertension (high blood pressure)
Please note: your cat may not display all of the symptoms listed above. Any of the above symptoms warrants a visit to the veterinarian.
hyperthyroidism in cats
Note the skinny appearance of this cat. Her fur is also very rough/unkempt looking which is common. You may also notice that they feel extremely bony, especially along the spine.
What effects does hyperthyroidism have on the cat?
Increased levels of the thyroid hormones cause an increased heart rate. Cats may also have a heart murmur. It can lead to heart failure and kidney damage. High blood pressure, which can cause blindness. Untreated, it can be fatal.
Secondary hypertrophic cardiomyopathy can occur as a result of hyperthyroidism.
How is feline hyperthyroidism diagnosed?
Your veterinarian will observe your cat's clinical signs, palpitate the thyroid gland. Other diseases such as renal failure and feline diabetes have similar symptoms, so it is necessary to take routine and specific blood tests to detect elevated levels of the hormones T3 and T4 are performed. Some cats with hyperthyroidism may show normal levels of these hormones in their blood test. If this is the case then a T3 suppression test may be performed. This involves taking a blood test to check the levels of T3 and T4, 7 oral doses of the thyroid hormone T3 and a blood test after the hormone was given. In a normal cat, the level of T4 will drop, in a cat with hyperthyroidism the T4 levels will stay the same or increase slightly. Cats with hyperthyroidism may also have elevated liver enzymes.
Thyroid imaging are another method.
Are some cats prone to hyperthyroidism?
No specific breeds are prone to feline hyperthyroidism, however is most often seen in older (8 years plus) cats.
There has been talk of a possible link between the consumption of canned food and hyperthyroidism in cats, but this doesn't appear to be the only cause as the disease can also occur in cats who don't eat canned food.
What is the treatment of feline hyperthyroidism?
There are three options to treat hyperthyroidism in cats. Each treatment has its pros and cons. Treatment should be depends on other medical conditions your cat may have (heart disease, kidney failure), availability of a nuclear medicine facility and cost.
Drugs (Methimazole/Tapazole): The use of medication doesn't cure hyperthyroidism, only controls it. Administered daily for the rest of your cat's life. There may be side effects from the use of drugs including vomiting and lethargy. Short term this is the cheapest option, but in the long run it can prove costly having to pay for daily medication for your cat. Methimazole can be given either in oral or transdermal (applied to the skin inside the ear) form. Advantages of medication are that treatment is reversible if side effects occur (see precaution at the end of this article). Other side effects may include; anorexia and vomiting.
Surgery: Removal of the enlarged thyroid lobe(s), known as thyroidectomy. Pros of this option are that it is a permanent cure. Cons include increased anaesthetic and surgical risks due to the effect the disease may have had on the cat's heart and kidneys. If both glands are removed, there is increased risk of accidentally removing the small parathyroid glands, (which among other things regulates the calcium supply in the body), which can cause hypocalcemia (low blood calcium). If both lobes are removed you will have to give your a daily thyroid supplementation.
Radioactive Iodine Treatment: This involves a single injection of radioactive iodine (radioiodine I-131). This concentrates in and destroys the diseased thyroid tissue, while leaving the normal thyroid tissue intact. Pros of this option are that the cat doesn't require anaesthesia, there is no need to give your cat medication for the rest of his life and in the majority of cases it is a permanent cure. In a few cases treatment will need to be repeated. No damage is done to the parathyroid glands. Cons are that it is expensive in the short term, and can only be performed at a specialist veterinary centre. After treatment your cat will be slightly radioactive and will have to stay at your veterinarian's until the radioactive levels drop.
In some cats, hyperthyroidism and kidney failure run concurrently. The hyperthyroidism can act to protect the kidneys. This is because hyperthyroidism produces a hyperdynamic cardiac state (increased blood flow), which increases glomerular blood flow (GBF) and glomerular filtration rate (GFR), improving renal function. Once treatment begins and the hyperthyroidism is brought under control, kidney failure may become worse. If kidney failure is suspected, your veterinarian will recommend using drugs to control the hyperthyroidism and closely monitor kidney function. That way, if the kidneys do begin to deteriorate, medication can be re-evaluated or stopped immediately, opposed to surgery or radioactive iodine treatment which is permanent.
- See more at: http://www.cat-world.com.au/feline-hype ... F6r7s.dpuf
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