Diabetes is a complicated condition caused by a deficiency of insulin which results in elevated blood glucose levels and glucose in the urine. Diabetes mellitus is most common in older cats. Neutered cats, male cats and obese cats are at an increased risk of developing this condition. Genetic predisposition to diabetes is well recognised in people, and recently there has been evidence, particularly from Australia and New Zealand, that genetics may play a role in the development of diabetes in cats. In these countries the Burmese breed has been identified as being predisposed to diabetes, and analysis of pedigrees has suggested that this is an inherited trait.
Normal actions of insulin
Insulin is produced by the pancreas which is a small organ located in the abdomen, close to the stomach and the liver. Insulin is released into the bloodstream where it travels to all the tissues of the body. Its main role is to enable cells to take up glucose (sugar) which is needed as an energy source. Insulin also stimulates uptake of various other substances including amino acids (building blocks for proteins), fatty acids (needed for making cell membranes), potassium and magnesium by tissue cells. In the liver, insulin has important roles which include production of glycogen (a carbohydrate energy store) and fat. Insulin also reduces the amount of glucose made and released by the liver.
In diabetic cats, there is a relative or absolute deficiency in insulin resulting in impaired glucose uptake by tissue cells which causes hyperglycaemia. As the cells are starved of glucose, they switch to using fat and protein as an energy source. This is facilitated by breakdown of body stores of fat and protein, resulting in weight loss and the accumulation of toxic waste products which can precipitate a diabetic crisis (ketoacidosis).
An absolute insulin deficiency may arise as a direct failure of the pancreas to produce insulin. However, in most diabetic cats there is a combination of insufficient insulin secretion by the pancreas and what is known as peripheral insulin resistance. Peripheral insulin resistance describes the situation whereby cells of the body fail to respond to insulin as effectively as they should. Insulin resistance can be caused by a number of conditions including pregnancy, obesity, some drugs (eg, corticosteroids such as prednisolone, progestagens such as megestrol acetate – ‘Ovarid';Virbac), other hormonal conditions such as hyperadrenocorticism (tumour of the pituitary or adrenal gland resulting in excessive production of corticosteroids by the body) and acromegaly (a tumour producing excessive amounts of growth hormone).
In diabetic cats, the hyperglycaemia is so severe that glucose is excreted in the urine . Glucose takes water with it so an increased volume of urine is produced. To compensate for this, and so that dehydration is prevented, the cat develops an increased thirst. Weight loss and a voracious appetite are also frequently seen and these may be the original reasons for presentation to a veterinary surgeon.
Therefore the main clinical signs seen in a diabetic cat are:
• Weight loss
• Increased appetite
• Increased drinking and urinating
These signs are not always present or may pass unnoticed. For example, the increased thirst may not be recognised if the cat is drinking from water sources outdoors while not noted to be drinking more in the home.
Other clinical signs which may be seen in diabetic cats include:
• Straining to pass urine and/or passing bloody urine associated with a bacterial urinary tract infection (bacterial cystitis)
• Enlargement of the liver evident on examination by a veterinary surgeon
• Poor coat
In a small number of diabetics, the nerves supplying the legs, and in particular the hind legs, may be affected resulting in a classic plantigrade stance (sunken hocks). Very rarely, the eyes may be affected by cataracts and retinal abnormalities which develop associated with the diabetes. This can cause problems with vision, including blindness in the most severely affected cats. High blood pressure is a recognised potential complication of diabetes in people and has also been reported in a small number of diabetic cats.
Most diabetic cats will remain well in themselves but ketoacidosis is a potential complication that can be seen in any uncontrolled diabetic. In this situation, the cat may become extremely depressed with signs such as vomiting, diarrhoea, complete loss of appetite, dehydration, collapse and coma. If any of these signs are seen in a diabetic cat, it is cause for immediate concern and a veterinary surgeon should be contacted as soon as possible (see later).
Diabetes mellitus is suspected in cats showing the appropriate clinical signs but other diseases may also cause similar signs. For example, other important causes of weight loss in an older cat including kidney disease, cancer, hyperthyroidism (overactive thyroid gland) and inflammatory bowel disease need to be ruled out. The earlier that diabetes can be detected the better and so routine urine checks in cats above 7 years old are recommended.
Blood and urine tests are required to confirm a diagnosis of diabetes. Although hyperglycaemia and glycosuria are found in diabetic cats, cats can also suffer from a stress-associated hyperglycaemia which can cause glycosuria and therefore confuse diagnosis. For this reason, a single blood or urine sample cannot be considered as diagnostic of diabetes. One solution to this problem is for the cat's owner to collect a urine sample whilst the cat is in its non-stressful home environment. The easiest way of doing this is to replace normal cat litter with non-absorbent cat litter (supplied by a vet) or clean aquarium gravel so that a sample can be collected. The urine sample can be taken to a veterinary surgeon for testing or the hospital may give you some test strips to use at home.
Diabetes mellitus is usually a treatable condition and although it requires considerable dedication and commitment from owners, it can be a very rewarding problem to manage.
Management of predisposing factors
Initial management may involve addressing factors which have precipitated or complicated the diabetes such as treating obesity or withdrawing drug therapy. If no predisposing causes of the diabetes can be identified, or if correction of these do not lead to resolution of the diabetes, then specific treatment is required.
Dietary management of diabetes
Underweight diabetic cats may need energy dense diets until their weight normalises. Obese diabetic cats should be put onto a weight loss regime, under the guidance of a veterinary surgeon, as obesity interferes with the way insulin works. In some of these cats, this may resolve the diabetes.
Research has shown that low carbohydrate and high protein diets can help to reduce the requirements for insulin and improve diabetic management. A variety of commercial petfood manufacturers produce prescription low carbohydrate diets suitable for use in diabetic cats.
It is recommended, as far as possible, to keep the diet constant both in terms of what is fed as well as timing of meals and so on. Altering the feeding regime may upset the stabilisation of the diabetes. However, it is not necessary to feed cats at strict meal times - it is fine to stick to the feeding regime that your cat is already used to.
In most diabetic cats, insulin therapy is required, at least initially. Insulin is given by an injection under the skin of the scruff and most cats will be stabilised on a regime involving either once or twice daily injections. The exact site of administration should be changed on a daily basis to reduce any scarring or reaction at the injection site which may limit insulin absorption. Special insulin syringes with very fine needles are used so that the cat will hardly feel the injection. Veterinary surgeons often recommend that diabetic cats are offered food just before they receive their insulin so that the cat is distracted by eating and does not notice the injection.
There are a number of different types of insulin available and different cats respond better to one type than another. The dose required by each cat is also very variable and it may take several weeks to stabilise the diabetes. Many veterinary surgeons will hospitalise diabetic cats undergoing initial stabilisation.
The long-term outlook for cats with diabetes mellitus varies according to how old they are, how easy it is to stabilise their diabetes, whether they have any other diseases and how severe these are. In one study, the average survival time for diabetic cats was around 2 years. Many diabetic cats have an excellent quality of life and are extremely rewarding cases to treat.