Diabetes mellitus ("sugar diabetes"/DM) is a common endocrine disorder in cats. There are two types of diabetes, type 1 — in which the pancreas doesn't produce enough insulin — or type 2 — in which the body's cells don't respond appropriately to insulin. Most cats have type 2 diabetes.
Insulin is a hormone produced by the pancreatic islet cells. When a cat eats, food is broken down into organic compounds in the small intestine, one of which is glucose. Glucose is taken up by the cells for energy, growth, and repair. As glucose enters the bloodstream, the pancreas matches it with the correct amount of insulin. Insulin is required to enable glucose to enter the cells, acting as a key to unlock it. When insulin arrives at the cell, it stimulates the cell to activate glucose transporters, pulling the glucose through the wall of the cell.
In type 1 diabetes, cells of the immune system attack and destroy islet cells which result in a decreased number of cells producing insulin.
In type 2 diabetes, cells build up a resistance to insulin (known as insulin resistance) and despite the pancreas producing enough insulin, it is unable to unlock the cells as efficiently.
When the cells don't have enough glucose either because there isn't enough insulin or the body resists it, they lack the energy required to enable the cat's body to work properly.
What happens in the diabetic cat?
Diabetes has many effects on the cat's body.
Glucose builds up in the bloodstream (high blood sugar), this is known as hyperglycemia.
Because the glucose is unable to enter the cells, the body is starved of energy and the cat begins to lose weight, despite having a healthy appetite. If diabetes goes untreated, the body will begin to break down its own fats and proteins to use as energy, leading to further weight loss. Ketones in the urine and blood are a by-product of the body's digestion of its own tissues. As the owner of a diabetic cat, you may be required to check your cat for ketones in the urine. This test is performed using strips (readily available from your chemist or veterinarian) which are dipped in the urine. The strip will change colour, which is compared to a guide on the back of the pack to determine if ketones are present. Ketones in blood or urine are a sign the disease has progressed. Ketoacidosis is a serious complication and requires immediate veterinary attention.
High glucose levels in the blood cause the cells to begin to malfunction due to lack of glucose; the cells become unable to reproduce themselves when their life spans are completed.
The kidneys try to remove the glucose from the blood, and high levels of urine are produced, which causes excess thirst in the cat. This is known as polydipsia (PD). Due to the higher workload placed on the kidneys, they are often the first organs to show signs of damage.
High blood sugar also has a damaging effect on the tiny blood vessels which nourish the retina. This is known as diabetic retinopathy and can cause sight issues from the range of mild vision problems to complete blindness.
Weakness in legs (neuropathy). Nerve cells are also susceptible to high glucose levels in the blood. Nerve, eye, and kidney cells do not require insulin to take up glucose, so in the diabetic cat, they may take in high levels of glucose. Weakness in the legs is caused by this nerve damage.
The earlier diabetes is detected, the less time the disease has had to damage the cat's body, so it is important to seek veterinary attention as soon as you see any changes in your cat.
What are the symptoms of feline diabetes?
Symptoms of diabetes include:
- Increased urination and thirst (PU/PD)
- Weight loss
- Increased appetite (polyphagia)
- Poor coat condition (dry/dull coat, dandruff)
- Weakness in hind legs
- Bad breath
Please note: Depending on the severity and length of time your cat has been a diabetic, you may not see all of these symptoms.
It is important to always be observant of your cat's general wellbeing, eating, and toileting habits; if you see anything out of the ordinary, seek veterinary advice as soon as possible.
What causes feline diabetes?
There are several reasons a cat may become diabetic. Obesity is the huge risk factor for the development of diabetes and sadly more and more cats are becoming overweight. Genetic predisposition can cause insulin resistance (type 1 diabetes is more commonly seen). Cushing's syndrome causes elevated blood sugar levels, which can lead to secondary diabetes. Pancreatitis results in the destruction of pancreatic cells, leading to a decreased number of cells able to produce insulin. Some medications (steroids) can also play a role in the development of diabetes.
How is feline diabetes diagnosed?
A tentative diagnosis may be made based on presenting symptoms. A physical examination from your vet may indicate diabetes such as enlarged liver (hepatomegaly) due to lipid accumulation, weight loss, poor coat condition, and dehydration can all point to diabetes (but may be caused by other diseases also). Presenting symptoms such as increased thirst and urination as well as weight loss may raise your veterinarian's index of suspicion.
Your veterinarian will perform routine screening tests such as complete blood count, biochemical profile, and urinalysis. Hyperglycemia (increased blood sugar levels) and glucosuria (increased sugar levels in the urine) may be revealed if your cat is diabetic. Ketonuria (ketones in the urine) may also show up in the urinalysis. The presence of ketones in the urine indicates that the disease has progressed.
Biochemical profile results may reveal hypokalemia (low blood potassium levels) and hypophosphatemia (low phosphate levels).
Measuring levels of fructosamine in the blood is another method to test for diabetes. Fructosamine is formed when albumin (a blood serum protein) and glucose bond together; this measurement gives an idea of average blood glucose over the preceding two to three weeks. Reduced total protein and hyperthyroidism can cause a decrease in the result. Chronic stress can cause a small increase, but not usually in the same range as diabetes.
Diagnosis based on a single blood test may prove inaccurate as it is possible for the blood to show elevated glucose levels as a result of stress (known as transient hyperglycemia). Therefore a diagnosis based on a single blood and/or urine test cannot give a definite diagnosis of diabetes. There are several solutions to this. Perform several blood and urine tests over time. Try to collect a urine sample from home, when the cat is not stressed.
Which cats are at risk of feline diabetes?
Diabetes can affect any cat of any age, breed, or gender. However, it is seen more often in obese and/or middle-aged to older cats. Male cats are affected more often than female cats. There appears to be a higher incidence of diabetes in Burmese cats.
How is feline diabetes treated?
There are many possible regimes for the diabetic cat, depending on the severity of the disease. The primary goal is to keep blood glucose levels under control. This can be a fine balancing act which requires careful monitoring to ensure levels don't become too high or too low.
Type 1 diabetes requires daily insulin injections.
Type 2 diabetes is treated with dietary management, reducing obesity and if necessary, daily insulin injections.
Diet: In mild cases, the cat may be managed with diet alone. If the cat is not ill and has no ketones, it may be possible to manage diabetes without the use of insulin. This may include dietary modification and/or careful weight loss under the supervision of your veterinarian. Cats in the wild mostly consume protein in their diet, however, most modern pet foods (especially dry foods) contain between 30-70% carbohydrates. A great deal of focus is now being placed on reducing carbohydrates in the diet by switching from dry food to canned food or home-prepared diets. In fact, some cats have had their diabetes reversed by switching to a low-carbohydrate diet. This is known as diabetic remission.
Oral hypoglycemic drugs (such as glipizide) may be prescribed. The exact mechanism of glipizide isn't known, but it is believed that it stimulates the pancreas to release insulin. This treatment is only effective if the pancreas is still producing some insulin.
Monitoring: Even though diabetes may be mild, careful monitoring of the cat is vital. If he becomes unwell, develops ketones, or remain persistently hyperglycemic, then the next step will be insulin.
Insulin: This involves the injection of insulin once or twice a day. It is administered subcutaneously (under the skin) at the scruff of the neck. These can be given at home, usually at regular, daily times. Individual cats respond differently to insulin, and doses may need to be adjusted based on blood glucose profiles, clinical response, and urine glucose monitoring.
Hypoglycemia (low blood sugar) is a potentially life-threatening complication of insulin therapy. This is caused by either too much insulin or the cat not eating enough food. The cat's blood sugar levels dip dangerously low. Feeding small but frequent meals will help avoid this condition, but careful monitoring of your cat's blood sugar levels is important. Signs of hypoglycemia include weakness, listlessness, lethargy, wobbly gait, convulsions, and coma. If left untreated, it can lead to death. If you notice any of these signs in the diabetic cat, you should offer it some food to eat. If this is not possible, rub a tablespoon of corn syrup onto his gums. Do NOT force fluid or liquids down the mouth, and keep your fingers be placed inside the mouth of a cat having convulsions or in a comatose state. You should notify your veterinarian immediately so that the insulin dose can be readjusted.
If properly managed, a diabetic cat can live for many years. In some cases, diabetes has resolved itself, in time. It is important to regularly monitor your cat and work closely with your veterinarian.