Feline Diabetes Mellitus Overview
Diabetes mellitus (DM), or simply diabetes, is a group of metabolic disorders in which blood sugar levels remain high for long periods of time. This occurs when there are insufficient levels of insulin produced in the body or the body isn’t responding properly to this hormone. Just like in humans, related to the modern-day lifestyle factors and obesity, a rising prevalence of diabetes has been described in cats too. Most recorded cases of feline diabetes are similar to the human diabetes type 2.
Diabetes is a group of metabolic disorders in which pancreas either doesn’t produce enough insulin or the body isn’t responding to the hormone appropriately.
The pancreas is a gland located near the feline stomach, attached to the wall of the small intestine. This gland has both exocrine and endocrine functions. Its exocrine function is the production of digestive enzymes trypsin and chymotrypsin. Its endocrine function is the production of the glucose-regulating hormones glucagon and insulin (Foster, 2018).
Insulin is a peptide hormone and it is produced by the beta pancreatic cells. This hormone promotes the absorption of glucose from the blood by the liver, fat and skeletal muscle cells. Once transferred in the cells, glucose is converted into glycogen, fats or both. Therefore, by regulating the absorption of glucose by the cells, insulin regulates the metabolism of carbohydrates, proteins and fats (Stryer, 1995). When glucose isn’t absorbed into the cells, its levels remain high in the blood for prolonged periods of time. Despite high glucose levels in the blood, the body cells are actually starving because glucose is one of the main energy sources for them. The danger of leaving diabetes untreated is that in the final stages of the disease, the body will eventually start breaking down its own fat and muscles for energy.
In humans, there are three main types of diabetes described:
1. Type 1 DM: this is the form of diabetes in which the pancreas itself fails to produce enough insulin. This type of the disease seems to be quite rare among cats.
2. Type 2 DM: in the early stages of this diabetes type insulin is being produced but the cells fail to respond to it. This is called insulin resistance. In later stages the insulin levels may drop. Most cases of feline diabetes are similar to this type of human diabetes.
3. Gestational DM: this is the type of diabetes that occurs in pregnant women without previous history of diabetes. This type hasn’t been described in cats yet.
Diabetes type 1 is caused by the detriment of the beta pancreatic cells. This is usually due to an autoimmune reaction in which the body attacks its own self. Exact causes for this are unclear but certain infections or toxins may be involved.
Diabetes type 2, just like in humans, is usually multifactorial. Obesity, insufficient exercise, aging and poor diet are all associated with this type of diabetes.
As diabetes progresses, certain complication may arise due to starvation and glucose toxicity:
Diabetic ketoacidosis (DKA). When there are low levels of insulin or there is an insulin resistance, the body is starving as glucose cannot actually reach the cells. This is dangerous because the cells use glucose as one of the main energy sources. If not diagnosed and treated, in combination with dehydration, fasting or infection, this state may lead to diabetic ketoacidosis (DKA). DKA is a diabetic complication usually observed in diabetes type 1, but may occur in type 2 too. In DKA, because of high glucose levels, glucose starts "spilling out" into urine. Along with it, glucose will take the water and some solutes such as potassium and sodium out of the body too. This is called osmotic diuresis and it leads to dehydration and excessive urination and drinking. On the other side, because of starvation, there is a release of free fatty acids from the body fat which are converted to ketone bodies (acetoacetate and beta-hydroxybutyrate). The ketone bodies disrupt the natural pH of the blood which actually leads to hyperventilation (the body is trying to cope with the acidosis of the blood by lowering the blood carbon dioxide levels) (Kitabchi A.E., et al 2009).
Diabetic neuropathy. Severe cases of diabetes may lead to the damaging of the peripheral nerves. This diabetic complication is known as diabetic neuropathy and the consequences include weak hind legs and struggles with walking and jumping.
Clinical symptoms of feline diabetes include sudden weight oscillations (usually sudden weight loss but sometimes even weight gain) and odd changes in appetite. Cats experience ravenous thirst and excessive urination. These are all consequences of the body being unable to use glucose as an energy source.
The glucose levels in the blood are significantly high (22-44 mmol/L) and glucose is present in the urine (glycosuria). In the later stages of the disease there will be ketone bodies present in the urine too. As the disease progresses, if the body starts breaking down its own fat and muscles for energy, the cat will also show signs of lethargy or limpness and acetone-smelling breath. In the end, if left untreated, diabetes leads to coma and death.
Feline diabetes is diagnosed in similar ways as in humans. Excessive thirst and urination, appetite and body weight oscillations, persistently high glucose levels in the blood and the glucose in the urine are all parameters to be on the lookout for when diagnosing diabetes.
High glucose levels in the blood: The normal glucose level range is from 4.4 to 6.6 mmol/L. While leaps in the glucose level after high-calorie meals can be tolerated, in diabetes, glucose levels may reach values as high as 22-44 mmol/L. For determining the glucose blood levels the same tests used on humans can be used on cats too. The blood for testing is usually sampled from the ear edges or paw pads.
Glucosuria: Glycosuria is a term used to describe presence of glucose in the urine. Glucose will not be found in urine in healthy cats because kidneys do not filter glucose from the blood unless there are excessive levels. When the levels of glucose in the blood are high, then glucose will start "spilling out" into the urine. This is why glycosuria can be observed in diabetic cats, but not in healthy ones and it is diagnosed in the same way as in humans.
Ketone bodies: in cases of progressed diabetes, ketone bodies may be detected in urine with the same urine strips as in humans.
Prognosis and treatment
Fortunately, if diagnosed timely and correctly, diabetes can be successfully controlled. It is very important to address this disease appropriately, because if left ignored and untreated, it is life-threatening.
Diabetes is commonly treated with insulin injections, usually applied long-term and twice daily. Cats can be treated with human synthetic insulin or bovine-based insulin (which is most similar to feline). More importantly, because diabetic cats suffer from disrupted carbohydrate metabolism, controlled and adapted diet is a critical component of the treatment. Diabetic cats should consume a diet very low in carbohydrates and rich in proteins and fats. This should prevent glucose level rises in the blood.
In some cases of feline diabetes, medications may be applied in efforts to stimulate the pancreas and promote the insulin release (i.e. Glipizide). Nowadays these treatments are used less frequently because recent studies suggested that these medications could be damaging the liver even more (Hoenig M. et al, 2000).
Predisposition to DM
A study published in 2015 by Öhlund M. and co-authors studied insured cats in Sweden and the association of DM with certain factors such as age, breed and sex. The results of the study suggest that male cats may be at a higher risk from diabetes than female cats. It also shows that domestic cats are more prone to disease in comparison to the purebred cats. When it comes to breeds, it suggests that the Burmese, Russian Blue, Norwegian Forest cat, and Abyssinian breeds may be at a higher risk from feline diabetes compared to other cats. No sex predisposition was found among Burmese cats (Öhlund M.et al, 2015).
1. How common is feline diabetes? – The true incidence is unknown and the disease seems to be broadly underdiagnosed. Some figures in literature range from 0.5 to 2% cats in the feline population (Eckstein, 2018).
2. Can feline diabetes be cured? – Diabetes generally cannot be cured but can be controlled. If diagnosed and addressed timely and correctly, diabetic cats can live happily and comfortably for many years to come. There are described cases of diabetic cats going into full or partial remissions too, but most commonly the condition is not the one we can really cure.
3. Do I have to give my own cat the insulin shots? – Yes, feline owners usually have to apply the insulin shots on their own. But no worries, once your vet teaches you how to do this correctly, it won’t be as challenging as it may seem at the moment.
4. How often do I have to test my cat’s blood? – Blood tests are usually done during the regular vet visits. But, if you wish, you can do the blood tests on your own more frequently.
5. What should I feed my diabetic cat? – Cats suffering from diabetes should eat diets low in carbohydrates and rich in protein and fat. It needs to be well balanced and you should make sure that they get all the amino acids they need. We recommend for you these great tips regarding the diet for diabetic cats from VetStreet.
Despite being a tough struggle, once appropriately diagnosed and treated, diabetic cats can lead happy and careless lives. If you ever notice any suspicious signs contact your vet as soon as possible, as diabetes is broadly under-diagnosed and timely diagnosis is crucial in the prognosis of the disease.
Eckstein, S. (2018). Feline Diabetes: Symptoms, Treatments, Prevention, and Diet Tips. Retrieved July 21, 2018, from WebMD: https://pets.webmd.com/cats/guide/feline-diabetes-symptoms-treatments-prevention-diet#1
Foster, R. (2018). Pancreas: Anatomy & Digestive & Endocrine Functions in the Cat . Retrieved from PetCoach: https://www.petcoach.co/article/pancreas-anatomy-digestive-endocrine-functions-in-the-cat/
Hoenig M, Hall G, Ferguson D, et al. (2000). A feline model of experimentally induced islet amyloidosis. Am. J. Pathol., 157(6), 2143-50.
Kitabchi AE, Umpierrez GE, Miles JM, Fisher JN. (2009). Hyperglycemic crises in adult patients with diabetes. Diabetes Care, 32(7), 1335-43.
Öhlund M, Fall T, Ström Holst B, Hansson-Hamlin H, Bonnett B, Egenvall A. (2015). Incidence of Diabetes Mellitus in insured Swedish cats in relation to age, breed and sex. Vet Intern Med, 29(5), 1342-7.
Stryer, L. (1995). Biochemistry. New York: Freeman and co. Ward, E., & Downing, R. (2015). Diabetes Mellitus in Cats - Overview. Retrieved July 21, 2018, from VCA: https://vcahospitals.com/know-your-pet/diabetes-mellitus-in-cats-overview