Introduction
Cushing’s disease (or syndrome) is not a common problem for cats and tends to occur in middle aged and older cats. The adrenal glands are very small relative to the weight of the animal and are part of the endocrine system. They sit on top of the kidneys, but are a fraction of the size. One of the functions of the outer layer of the gland, the adrenal cortex, is to produce cortisol, which increases blood sugar when the body needs it, suppresses the immune system and also helps metabolise carbohydrates, proteins and fats. It also produces androgens, a sex hormone and aldosterone, which regulates kidney function. The failure of these important tasks, when the adrenals are not functioning properly, gives rise to the various symptoms of hyperadrenocorticism.
Symptoms of Hyperadrenocorticism
The symptoms are many and may not all occur at once or at all. The overproduction of aldosterone interferes with proper urinary output, meaning that the cat may exhibit extreme thirst, with the accompanying increase in urine output. The cortisol imbalance will cause dietary problems, usually overeating, with muscle wasting. The abdomen may become enlarged, with lack of evacuation of the bowel and also fluid retention. The increased sex hormones will result if fur loss, usually on the flanks as well as thinning skin which can be damaged with a very slight injury. It is unlikely that the cat will show all of these symptoms before a concerned owner will take it to the vet.
Causes of Cushing’s
There are three basic reasons why your cat will develop Cushing’s disease (syndrome). The first is that it is being medicated with corticosteroids for another condition. This may have been injected or it may be a long term treatment orally. Sometimes, creams for various skin conditions contain a quite high dose of corticosteroids. This type is called iatrogenic Cushing’s, or veterinarian induced Cushings. If the animal is on any medicine containing cortisol and shows the symptoms treatment is relatively easy; the medication should be gradually reduced until symptoms cease. It is essential that the medication is reduced slowly, to give the adrenal cortex time to recover, or it could create even more problems.
The second type of hyperadrenocorticism is caused by a tumour of the adrenal cortex which can be benign or malignant. Cushing’s Disease in this instance is simply caused by there being too many adrenal cortex cells and so the production of the hormones is increased. This is also known as adrenal dependent hyperadrenocorticism. The third type is caused by a pituitary tumour. Any tumours in the pituitary cause the adrenal glands to overproduce and this is known more correctly as Cushing’s Syndrome or pituitary dependent hyperadrenocorticism. The symptoms of all three are essentially the same and the vet will order tests to determine which cause to deal with.
Treatment of Hyperadrenocorticism
Treatment will very much depend on which type it is and the results from the various blood tests and diagnostic imaging will define where the problem lies. If medication is the problem that can be dealt with by re-prescribing and reducing the dose. Unfortunately of course, the corticosteroids could be prescribed for a serious disease in the first place, which will mean a re-evaluation of the treatment of the animal and may have a serious impact on the final outcome. If there is a tumour in the pituitary gland, then this will give the vet and owner different problems to discuss, but to stop the general debilitating impact of it on the adrenal cortex, the only resort is to remove both the adrenal glands.
If there is a tumour in just one adrenal, it is enough to remove just that one and this also makes after care easier, as the remaining gland may well function perfectly well. If there are no adrenals left after treatment, the cat will have to have lifelong hormone replacement. This can be quite complex, as the medulla (inner portion) of the adrenals produces hormones which monitor the body’s response to stress – usually known as adrenaline – and replacing this is very difficult, as it needs to be present in different levels depending on what is happening to the animal on a minute by minute basis.
Prognosis
Every case is different and many vets and owners will decide to try surgery and subsequent drug regimes. These can be successful but the removal of the adrenal glands is a notoriously tricky procedure, partly because they are so small, partly because of their very close proximity to the easily damaged kidney and partly because the operation is not done routinely even in a very busy veterinary practice. The other contraindication which may be present is the cat’s age. If it is old – and Cushing’s is more common in older cats – it may have other underlying health problems which preclude the likelihood of successful surgical outcomes. Finally, not all cats tolerate medication well and if your cat is likely to get stressed just by being given a tablet or injection, it would not be a good candidate for an adrenalectomy. But if, when everything has been taken into account, the owner and the vet decide that surgery is appropriate, many cats have made a reasonable recovery.
