Monday, July 10, 2006

The Cat is Getting Old

It has happened so many times. A client brings in a thin, scraggly 14 or 15 year old cat. She has been with the family for years and they love her dearly. They say the cat has been losing weight over the last couple months, but has been eating well, so they didn't think anything of it. They just thought she was getting old. She is now skin and bones so they think she may need to be put down, but look hopefully at me to see if there is anything that can be done.

I ask my usual questions as I examine her. The answers are familiar: yes she is always hungry, yes she seems to have a lot of energy for her age, yes she occasionally throws up but we thought it was hair balls, yes she is restless at night. The exam reveals bad teeth, bright eyes, a racing heart rate, a heart murmur, severe muscle wastage and no body fat... and a large lump in the neck to one side of the trachea.

I inform the client that I will need to do some tests to confirm, but that I suspect the cat is getting old and is suffering from one of the most common "old-cat diseases": hyperthyroidism. Fortunately it is completely treatable and often carries an excellent prognosis.

I find the three most common "old-cat diseases" are kidney disease (failure/insufficiency), hyperthyroidism and cancer (various types). Each of these diseases can be treated if they are caught early enough and managed to maintain the quality of life of your beloved moggy for many years after diagnosis.

Hyperthyroidism is caused by an over-active thyroid gland. The gland is shaped like a butterfly and is located on either side of the trachea (windpipe) on the front of the neck. Often one side overacts first and the second side follows a year or two later. Because thyroid hormone regulates the metabolic rate of the cat, too much thyroid hormone makes them burn calories much faster than they can take them in. They become very hungry and very active/restless. Because they can't take in enough calories, they start to burn all their fat reserves, and when those are gone, they start to burn muscle.

Thyroid hormone also increases the heart rate. A normal cat who is nervous in my exam room will have a heart rate of between 160-200 beats per minute. I have counted heart rates of 240-260 in some hyperthyroid cats. The heart starts to wear out from all the hard work it is doing. Initially you just hear a murmur, but eventually the cat can go into heart failure and this is usually what kills the cat if the thyroid is left untreated.

I diagnose hyperthyroidism with a simple blood test. I always test the kidney and liver enzymes as well and monitor these throughout treatment. The high blood pressure associated with a rapid heart rate can mask an underlying kidney disease. This then becomes apparent once the heart rate and blood pressure are brought down to within the normal limits.

I start treatment with tablets given once, twice or three times per day depending on how high the thyroid levels are. I always check the patient 2 weeks after starting treatment to make sure they are not suffering any adverse side-effects (dramatic loss of appetite, lethargy, vomiting or itchy skin for example) and to adjust the dose accordingly. After a further 2 weeks, I check the thyroid hormone level and kidney values. Once the patient is stabilised we discuss further options. Cats, if they tolerate the tablets, can stay on them indefinitely. I prefer to surgically remove the overactive thyroid since most cats do not reliably take their tablets! There is also the option to use radioactive iodine to irradiate the thyroid tissue, but I have yet to have any clients take me up on this option. (It requires the cat to be hospitalised for a month since her urine and faeces are radioactive for this length of time after the treatment. It also costs over £1200, while the surgery is more like £250 per side and only requires an overnight stay in hospital).

I have only ever had to start 1 patient on thyroid supplementation after removing the thyroid and I have only ever had one patient experience the most serious side effect of surgery which is damage to the parathyroid and subsequent hypocalcaemia (resulting in fits/seizures which resolved with calcium supplementation). If you do opt to have your cat’s thyroids removed, please be aware that they can still be hyperthyroid. Some cats seem to make thyroid tissue elsewhere in the body. These cats can only be treated with tablets or radioactive iodine. Sometimes the thyroid is also located in the chest rather than the neck. These cats cannot have the operation.

So the long-and-the-short of this post is... if the cat seems to be getting a bit old and thin, get her checked sooner rather than later -- she'll thank you for it!

Please note: prices vary widely in different parts of the country and world. The prices mentioned here were examples from two veterinary surgeries in the Southeast of England.

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