Category: hormonal-diseases-cat

Hyperthyroidism was first seen in cats as recently as 30 years ago and appears to be caused by a form of benign cancer in the thyroid gland. However, it is still not clear what causes the cancer to develop. The disease is rare in young cats but becomes more common in later life. It is now the most frequent hormonal disease in middle-aged and older cats.

The first indication that anything is wrong is usually a marked increase in your cat’s appetite. Even though your cat is eating more it may lose weight and its coat may become rough and unkempt. Other changes include restlessness and aggression, body tremors, increased drinking and urinating, vomiting and diarrhoea. In about one case in ten the symptoms are unusual and the opposite of what might be expected, such as depression, loss of appetite and physical weakness.

Apart from recognising the symptoms, there are a number of other steps in making a diagnosis. When your vet examines your cat’s throat the thyroid gland may feel lumpy or enlarged. Blood tests are usually taken to rule out other diseases of the liver or kidneys. Directly measuring levels of hormone in the blood may help confirm the diagnosis but in some cats the thyroxine levels may be normal. Your vet will also want to check your cat’s heart – an abnormally fast or irregular heart beat is often a feature. Early diagnosis and treatment is important to prevent and even reverse damage to the heart and kidneys.

Medication

There are drugs available which block the production of hormones by the thyroid gland. The medication is given one to three times a day.

Advantages

• Simple and does not require an anaesthetic
• Suitable for cats with severe kidney disease, which might be made worse by the other types of treatment

Disadvantages

• Does not tackle the underlying problem and so treatment must continue throughout your cat’s life
• Difficulties in getting your cat to swallow tablets
• You must remember top give the tablets every day
• In some cats there are side effects of the drug ranging from fatigue to anaemia
• In the early stages your cat must be carefully monitored to make sure that the dose is right

Surgical

The abnormal gland can be surgically removed.

Advantages

• Treatment should permanently cure the disease so no need for further medication

Disadvantages

• Not suitable for all cats, such as those with severe kidney disease or the very elderly
• Your cat may need drug treatment for a few weeks beforehand to show that its kidneys will cope and to stabilise their condition before anaesthesia
• Needs a general anaesthetic which is always a slight risk but more so in ill animals
• Possibility of damaging the parathyroid glands, which lie close to the thyroid and control the use of calcium in the body, so needs an experienced surgeon
• After surgery cats should be carefully monitored for a couple of weeks to make sure there are no changes in blood calcium caused by parathyroid gland damage

Radiation

An injection of radioactive iodine will destroy the abnormal thyroid tissue while leaving normal cells unaffected.

Advantages

• No anaesthetic required and very few unwanted side-effects
• A single treatment will permanently cure the disease in 9 out of 10 cases and a second treatment will do the trick in most of the rest
• Radiation will also work in much rarer cases in which the tumour is malignant or where a portion of thyroid tissue has broken away from the main gland and is normally missed during surgery

Disadvantages

• Availability – there are only a few places offering the treatment because of tight regulations covering the use of radioactive substances and there is likely to be a waiting list
• Your cat will have to stay in complete isolation until the radiation level has died down, usually around four weeks
• Your cat cannot be handled during this time and so this method is unsuitable for cats needing urgent treatment for other serious conditions
• The cost of treatment and prolonged boarding can be high

The decision on which method to choose should be made after careful discussion with your vet. Each has advantages and disadvantages and not all may be suitable for your cat. There are a number of things to consider, your cat’s age, the severity of the condition, the presence or absence of other diseases and the risk of complications, etc. Cost may also be a factor as both surgery and radiation treatment can involve a significant expense. However, medication may also be costly in a cat diagnosed with the disease relatively early in its life and treated continuously for several years.

Diabetes is a disease caused when there is not enough insulin in the body. Insulin is a hormone which keeps blood sugar (glucose) at an optimum level. When there is a lack of insulin, sugar from food builds up in the blood and eventually starts to appear in the urine.

Animals with diabetes have high blood sugar levels and lose sugar in their urine. They are more thirsty than normal and often lose weight despite having a good appetite. If the condition is untreated, liver disease, problems walking or other illness may develop. If the early signs of diabetes are missed, more serious signs such as vomiting and depression may develop. If diabetes is left untreated for weeks or months your cat could go into a coma and die.

If your cat has been diagnosed as a diabetic you may be wondering if you have done something wrong. Unfortunately some cats are just more likely to develop the disease than others. Male cats are most likely to get diabetes but any cat can be affected. Obese cats are slightly more likely to develop the disease, but there are many obese cats who do not develop diabetes.

Some other diseases can cause diabetes to develop and your vet will check to make sure your cat is not suffering from anything else. In a few cases treating the other disease will make the diabetes go away for a while, but it is quite likely to come back again later.

Most diabetic cats require regular insulin injections to control their blood sugar levels. Diabetes rarely goes away completely and so these injections must be given on a regular basis (usually once or twice a day), for the rest of your cat’s life. Your vet may need to help you work out a new diet and management plan for your cat. Injections should be given at set times each day but this can be arranged so that it fits into your usual schedule. Once the whole treatment schedule has been set you will have to stick to it in the future.

Most diabetic cats will need insulin injections to treat their diabetes at some stage. In some obese cats weight loss may control their diabetes for a while. A few other cats can be managed by careful weight control and by giving tablets which lower blood sugar (hypoglycaemic drugs). Although you may be worried about having to give your cat injections – most owners find that, with practice, it is easier to give their cat an injection than a tablet.

Insulin is a protein and (as with any other protein), can be digested. If insulin were given as a tablet, the tablets would be digested by the acid in the stomach and the insulin would have no effect. Insulin injections are given under the skin and do not hurt. VetPens, similar to the epipens used in human diabetes, are now available for cats. Along with insulin cartridges, they allow pet owners to give insulin with minimum preparation time.

Most people are naturally concerned that they will be unable to give injections to their pet. Your vet will teach you how to do this and within a few weeks most owners of diabetic pets are happy to give the injections at home. Until you are confident your vet will probably see you every day at the veterinary surgery and help you give the injections.

Your cat should be regularly monitored to make sure it doesn’t gain or lose weight. Your vet needs to examine your pet regularly and review their notes to see how your pet is progressing. Your vet will probably ask you to monitor how much your cat drinks to help monitor progress. At other intervals your vet may want to take blood samples from your cat – and may need to keep your pet in hospital for a day to do this. If you have any concerns about any aspect of your pet’s treatment discuss them with your vet.

There are two important complications which you must be aware of:

• Low blood sugar (hypoglycaemia): If this is untreated it may result in permanent brain damage. Symptoms develop rapidly with restlessness, confusion, tremors, twitches, convulsions or coma being the main signs. Sugar should be given by mouth, dissolved in water or as lumps. If your pet is still awake it may be offered food and should eat voluntarily. Contact your vet immediately if these signs develop.
• High blood sugar (hyperglycaemia): This usually develops more gradually and your pet may become unwell over a number of days. As the disease progresses your pet may go into a coma, although will not respond to sugar solutions. Contact your vet immediately if your pet is unwell and they will probably want to admit him.

Cushing’s disease is caused by prolonged exposure of the body’s tissues to high levels of the hormone cortisol. It is called Cushing’s disease because it was named after a famous neurosurgeon, Harvey Cushing, who first recognised it. It is also sometimes called“hyperadrenocorticism” or “hypercortisolemia”.

Cushing’s disease is caused by an excess of the steroid hormone, cortisol. In the normal cat cortisol is produced by the adrenal glands, (which are located just in front of the kidneys). Scientists think that cortisol has hundreds of possible effects in the body. Among its other vital tasks, cortisol helps to:

• maintain blood pressure
• slow the immune system’s inflammatory response
• balance the effects of insulin in breaking down sugar for energy
• regulate the use of proteins, carbohydrates and fats in the body

Because cortisol is so vital to health, the amount of cortisol produced by the adrenal glands is precisely balanced. Cortisol production is regulated by hormones produced in the brain (from the pituitary gland). The hormones produced by this gland stimulate the adrenal glands. When the adrenal glands receive the signal from the pituitary they respond by producing cortisol. In the normal animal cortisol is produced mainly at times of stress – in Cushing’s disease the levels of cortisol in the blood are always too high.

Cushing’s disease can occur following long-term treatment with corticosteroid drugs (so called ‘iatrogenic cushing’s’) or as a naturally occurring disease. The majority (approximately 85%) of naturally occurring cases of Cushing’s disease are caused by a tumour in the pituitary gland. Although this is, strictly speaking, a brain tumour the tumour is usually tiny and benign and causes no effects related to pressure in the brain. A smaller proportion (approximately 15%) of naturally occurring Cushing’s disease cases are caused by a tumour in the adrenal gland.

The two forms of natural Cushing’s disease are:

Pituitary-dependent Cushing’s disease

A tumour in the pituitary causes excess production of the hormone, adrenocorticotropic hormone (ACTH) resulting in enlargement of both adrenal glands.

Adrenal-dependent Cushing’s disease

A tumour of the adrenal gland makes one gland grow bigger and it is therefore able to produce more cortisol.

The signs of Cushing’s disease are extremely variable and can be subtle in the early stages. Cushing’s disease usually affects older pets (average age is 10 years but cats as young as 4 have been diagnosed with this condition).

Because the changes come on slowly it is sometimes easier to spot them if you do not see an animal every day. Often it will be your vet who examines your pet during its annual or bi-annual examination and points out that changes have occurred since your last visit. Many owners do not recognise the signs of Cushing’s disease in their pet, instead confusing the changes caused by the disease with signs of ageing.

The steroid hormones affect almost every tissue in the body and the signs of Cushing’s disease can be diverse. One of the most common problems associated with Cushing’s disease in the cat is diabetes mellitus. In fact most cases of Cushing’s in the cat are recognised because they are being treated for diabetes. The most obvious signs of diabetes are increased thirst and weight loss despite a good (or even increased) appetite. If your cat is drinking more or losing weight you should always take them to the vet for a check-up.

Typically, the diabetes seen in cats with Cushing’s is very resistant to insulin so high doses are needed to control the disease. Affected cats are also often reported to be lethargic and lacking energy. A small proportion of cats with Cushing’s are not diabetic although they may still show signs of increased thirst and increased urination.

Enlargement of the abdomen (a pot bellied appearance) is common and Cushing’s disease can cause changes to the skin and haircoat. The skin may become fragile and thin, lose hair, bruise easily and heal poorly. Minor trauma (grooming or handling) may result in skin tearing and wounds. Often affected cats have a poor haircoat. The tips of the ears may start to curl over.

High levels of steroid hormone in the blood suppress the immune system and healing process; so animals with Cushing’s disease may have repeated infections or wounds that do not heal as quickly as expected.

Iatrogenic Cushing’s is usually straightforward to diagnose as there is usually a history of long-term corticosteroid administration. However, cases of naturally occurring Cushing’s disease can be very difficult to confirm. Your vet may suspect the disease based on simple blood tests but specific blood tests are needed to confirm the diagnosis. These special tests measure the level of cortisol in the blood. However, because the levels of this hormone vary from hour to hour in a normal animal, the disease cannot be diagnosed on the basis of one blood test.

Your vet will need to take a number of blood samples before and after injection of hormones that affect the amount of cortisol produced by your cat. Some of these blood samples have to be handled very carefully and will need to be sent away to veterinary laboratories for analysis.

Ultrasound examination of the abdomen allows your vet to measure the size of each adrenal gland. If a tumour is present in the adrenal gland this should be visible on the ultrasound (and one adrenal gland will appear larger than the other). If the disease is caused by a tumour in the brain then both adrenal glands will be larger than normal.

X-rays may also be needed to show other potential problems caused by the disease.

Examination of a urine sample can be useful in a cat with Cushing’s disease – high levels of cortisol in the blood can cause diabetes mellitus and your vet will want to check for sugar in the urine to rule this out.

Treatment of iatrogenic Cushing’s is relatively straightforward with gradual reduction in corticosteroid administration required. Corticosteroids are potent drugs and it is essential that they are not stopped suddenly. In some cases, successful treatment of iatrogenic Cushing’s can take several months.

Treatment of naturally occurring Cushings disease in the cat is difficult and not without risk. Surgical removal of the abnormal adrenal gland (adrenalectomy) is the treatment of choice for adrenal Cushing’s disease. This is high risk surgery as affected cats are prone to infections and poor wound healing; there are high risks of bleeding at surgery as the adrenals are close to major blood vessels and cats with Cushing’s are more vulnerable to forming blood clots (thrombi) which can have serious consequences.

Pituitary cases are even harder to treat as there is no single perfect treatment. Medical treatment can be problematic in these cats – most of the treatments that have been tried have had poor success, side-effects can be seen and the drugs used are often not licensed veterinary treatments. Radiation therapy has been tried by some clinicians but is not widely available. Surgical removal of the pituitary, the treatment of choice in people with pituitary tumours, is a very high risk surgery that is not often performed in cats.

For these reasons, surgical removal of both of the adrenal glands may be recommended to prevent further cortisol production. This surgery is difficult and should be performed by a specialist in veterinary surgery, but in some cases medical treatment is given before surgery to stabilise the cat. In addition to the risks of surgery itself, it is very important that animals are closely monitored immediately after surgery and they may need to spend time in an intensive care facility.

Most animals with Cushing’s disease are middle-aged or elderly and owners sometimes ask if it is worth treating them. The outcome for cats with Cushing’s disease with treatment is not good. Even with successful treatment fewer than half of all cats will live for more than a year after diagnosis. Unfortunately if a cat had diabetes before treatment for Cushing’s disease there is only a 50% chance that the diabetes will resolve with treatment of the Cushings. Some cats will need to be given insulin to control the diabetes for the rest of their lives. Without treatment the complications can be significant and will seriously affect the quality of your pet’s life.

Acromegaly is caused by the production of too much ‘growth hormone’, which, as its name suggests, stimulates body tissues to grow. If too much growth hormone is produced it causes many tissues in the body to grow bigger, causing problems for the cat. Growth hormone also interferes with the way insulin works and so cats with acromegaly often have diabetes that may be very difficult to control and they may need a higher dose of insulin than expected in ‘normal’ diabetic cats.

Growth hormone is made in a specialised part of the brain (the pituitary gland). The amount of growth hormone in the body is normally carefully controlled. When there is enough growth hormone, signals are released that tell the pituitary gland to stop producing any more. Acromegaly is usually caused by a small cancer in the pituitary gland that continues to produce growth hormone despite the signals telling it to stop.

Acromegaly usually affects middle-aged or older cats (8-14 years) and males more often than females. The physical signs of acromegaly can be difficult to see and the changes come on very slowly, so an owner, seeing their cat every day, may not notice alterations in its appearance. Sometimes you can only see how much your cat has changed by looking back at photos of your cat taken some years ago. Acromegaly often causes widening of the face – which is sometimes easiest to appreciate by looking at the teeth (which move apart as the bone grows, widening the space in between the teeth).

In many cases owners first notice there is something wrong with their cat when it develops the signs of diabetes (excessive drinking and urination and increased appetite). Your vet may first diagnose your cat as having simple diabetes and prescribe insulin injections. If, after a period of time, your cat does not seem to be responding as expected to the injections your vet will want to do further tests. If it is discovered that your cat is resistant to the effects of insulin then a diagnosis of acromegaly may be suspected.

Your own vet may make the diagnosis of acromegaly or they might refer your cat to see a specialist for investigation of one of the problems caused by acromegaly.

Your cat’s appearance may make a vet suspicious of acromegaly. It is likely that your cat may already have been diagnosed as having diabetes, but if not blood tests may show abnormally high levels of sugar (glucose) in the blood and sugar in the urine. Serial blood tests may also show that your cat is not responding to insulin injections as well as expected.

X-rays and ultrasound may show that your cat has an enlarged heart (or, if changes have been present for a long time, even heart failure), or changes to the kidneys bones and joints. Blood tests can measure the levels of hormones in the blood but these often have to be sent to specialist laboratories and it can take some time to get a result back.

A scan of the brain (CAT scan or MRI) can be used to try to visualise the growth in the pituitary gland, and this scan will be necessary if you are considering having treatment for your cat.

Removal of the cancer in the brain is difficult – it would be unusual in the UK for surgery to be performed. Some centres can use radiotherapy to direct a beam of radiation into the cancerous growth in the brain. In cats, so far, no obvious side effects have been noted and the treatment seems to be tolerated extremely well.

Radiotherapy can only be performed at specialist centres and requires a general anaesthetic. If you decide to have this treatment you would have to take your cat along to the centre for a number of treatments over several weeks (or your cat may be able to board in the hospital for the duration of treatment).

Drugs that inhibit growth hormone production can be given as tablets – unfortunately these are not usually very effective.

If the cancer can be destroyed then the high level of hormones will drop and the signs of acromegaly hopefully resolve slowly. However some organs may have already been too damaged at the time of diagnosis to recover fully, and some changes may persist even after treatment. Often insulin requirements will go down a lot in diabetic cats, but your cat may still require insulin injections daily. In a significant number of cats the diabetes resolves completely or the signs relating to the growth in the brain improve due to the shrinkage of the growth.

If the disease is not treated more serious problems like kidney disease, high blood pressure, permanent diabetes, joint problems, seizures and heart problems can develop. On average cats with acromegaly live around 18 months from diagnosis if they receive no treatment. They will almost certainly suffer from diabetes and this may be very difficult to control with insulin injections. However it is important to persevere with insulin treatment as without this the signs of diabetes would be even more severe. Most cats eventually die as a result of other complications of the disease such as heart or kidney failure.