A condition on the rise - Veterinary Practice
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InFocus

A condition on the rise

SUSAN McKAY discusses the increase in diabetes mellitus and its treatment

DIABETES mellitus is a condition that clinicians are increasingly likely to diagnose in the next few years. In 1970, veterinary hospitals in the US reported 19 in every 10,000 dogs were diagnosed with diabetes but by 1999 the same hospitals reported 58 in 10,000 dogs were diabetic.

A similar pattern is reported in cats. The company Cat Professional aims to launch a book on the topic at the end of this year. Founder Dr Sarah Caney explains, “Many feline specialists feel that diabetes is on the increase in the UK cat population – probably in part because of the increasing number of obese cats. Also most vets are now very comfortable in making this diagnosis (and aware of potential diagnostic pitfalls such as the ‘stress hyperglycaemia’ that cats get).

“Although hyperthyroidism remains the most common feline endocrinopathy seen by most UK vets, there is a possibility that diabetes could overtake it in the next few years. At the moment, the most recent data we have for prevalence suggests the overall prevalence is 1 in 230 cats. 1 ”

The reasons for the rise in both cats and dogs have received a significant amount of attention. Canine diabetes is likely to have a strong genetic basis but it has been suggested that the seasonal incidence of diagnosis – one study has suggested that, as in humans, more canine cases tend to be diagnosed in winter – could indicate that environmental influences have a role in disease progression just prior to diagnosis2 .

At least 50% of canine cases are thought to have type 1 diabetes, the â-cells being destroyed in an immune-mediated process as evidenced in the detection of antibodies to â-cells, while the remainder are likely to be diabetic as a result of pancreatitis, dioestrus induced diabetes, chronic insulin resistance or other types.

Most diabetic cats show most similarities with type 2 diabetes in humans and type 1 remains rare.

The effects of obesity

Type 2 diabetes, where there is both peripheral insulin resistance and insufficient insulin secretion, is common in obese people. A 2006 study identified that weight and body condition scores were significant risk factors for the development of diabetes mellitus in dogs but this was a view that was contested in an earlier review by Rand (2004) who observed that canine obesity caused insulin resistance but there was no evidence to suggest that this developed into absolute insulin deficiency or overt diabetes 3, 4 .

Obesity is, however, a risk factor for the development of pancreatitis in dogs, a condition that is likely to be responsible for around 28% of cases of canine diabetes. In cats, obesity is a significant risk factor in the development of type 2 diabetes. There is some evidence to suggest that some individual felines have a genetically determined lower insulin sensitivity and even marginal weight gain can cause them to develop impaired glucose tolerance, putting them at increased risk of developing diabetes.

One of the theories as to the cause of type 2 diabetes in cats is that peripheral insulin resistance is present and “glucose toxicity” depletes secretory function of the pancreas.

It has been suggested that the diet and lifestyle of the modern day cat may be partly behind the increase in numbers of feline diabetics. A less active life indoors, rising levels of obesity and the shift from a high protein-low carbohydrate to a moderate/high carbohydrate diet may place an increased demand on â-cells, leading to excessive insulin secretion, eventually resulting in exhaustion.

Treating diabetics

Although there tends to be individual variation in response to insulin types, structurally dog insulin is most like pork insulin and cat insulin more like beef insulin. Protamine zinc insulin of bovine origin is considered to be the best option for cats and lasts longer, for around 12-14 hours, with less of a peak than other types.

A synthetic analogue, glargine, may offer some benefits as its “peakless” character suits the feline preference for feeding little and often, although in the absence of a licensed preparation, it has to be used off licence.

Transient cases

In at least 25% of feline cases diabetes is transient and will resolve in 1-3 months. This is probably due to the reversal of the effects of glucose toxicity and suggests that it is worth putting in place protocols that encourage early detection. These transient cases are also reported to be more likely to be associated with ketoacidosis.

The benefits of feeding a low carbohydrate-high protein diet to diabetic cats is well established but it has also been suggested that feeding a higher protein diet to cats at risk of developing diabetes could be beneficial3 . Although once daily dosing of insulin is reported in dogs, this probably applies to only 10% of patients and most need twice daily dosing to achieve adequate control 5 .

A high fat diet which results in lipaemia and disturbances in lipid metabolism have been implicated in obesity associated pancreatitis and may play a role in the development of pancreatitis in diabetic dogs. High fat diets may also impact adversely on insulin secretion and efficacy.

1. McCann, T. M., Simpson, K. E., Shaw, D. J., Butt, J. A. and GunnMoore, D. A. (2007) Feline diabetes mellitus in the UK: the prevalence within an insured cat population and a questionnaire-based putative risk factor analysis J Feline Med Surg. 9 (4): 289-99.

2. Atkins, C. E. and MacDonald, M. J. (1987) Canine diabetes mellitus has a seasonal incidence: implications relevant to human diabetes. Diabetes Res. 5: 83- 87.

3. Rand, J., Fleeman, L., Farrow, H. A., Appleton, D. J. and Lederer, R. (2004) Canine and Feline Diabetes Mellitus: Nature or Nuture, J Nutr 134: 2,7072S- 2,080S.

4. Klinkenberg, H., Sallander, M. H. and Hedhammer, A. (1987) Feeding, exercise and weight identified as risk factors in canine diabetes mellitus. The Journal of Nutrition 136: 1,985S 1,987S.

5. Church, D. B. (2008) Diabetes – what’s new? WSAVA/ FECAVA World Small Animal Congress Proceedings, pp228 -230.

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