Royal Veterinary College research, published in the journal PLOS ONE, has revealed that 1 in 4 cases of Diabetes Mellitus in domestic cats are caused by excess secretion of pituitary growth hormone.

According to the researchers, this is much more common than previously thought. Furthermore, they say that cats with this condition are easily misdiagnosed as having primary (type 2) diabetes mellitus but do not respond to the standard treatment to that condition, resulting in increased morbidity and ultimately leading to euthanasia on welfare grounds.

Researchers collected data between 2003 and 2011 on cats treated at vet practices across the UK, to estimate the prevalence of hypersomatotropism or acromegaly in the largest cohort of diabetic cats to date and look how easy this is to recognise.

Findings revealed that the presence of Diabetes Mellitus in 1 in 4 domestic cats can be explained by hypersomatotropism, which is caused by a pituitary benign tumour and can be effectively treated by one operation in specialist centres.

However only 24% of clinicians who submitted samples suspected that this was the case, as most hypersomatotropism cats did not display typical signs, instead displaying symptoms indistinguishable from cats with primary (type 2) Diabetes Mellitus. This suggests that hypersomatotropism screening should be considered when treating diabetic cats.

Lead researcher, Dr Stijn Niessen from the Royal Veterinary College, said: "It has been common practice to automatically suspect a cat with Diabetes Mellitus to be suffering from a form of diabetes akin to human type 2. The current study suggests that this is an oversimplification. Approximately one in four of assessed diabetic cats were actually found to be suffering from hypersomatotropism-induced Diabetes Mellitus, which requires specific treatment and manifests itself very differently as it develops.

"Interestingly, only a small proportion of clinicians reported they strongly suspected acromegaly to be present on the basis of the clinical picture. These data therefore highlight the need for veterinarians working with the spontaneously diabetic cat to consider routinely screening for the presence of hypersomatotropism-induced Diabetes Mellitus, given the significant clinical consequences of its presence.

"Should the hypersomatotropism be diagnosed and treated with one operation, most cats will enter a state of diabetic remission. If it remains undiagnosed, diabetic cats tend to be difficult to regulate glycaemically which often results in euthanasia, or in the long-term, they will suffer from other growth hormone-induced negative conditions such as heart disease, as well as central nervous system problems."

Evaluation of serum fructosamine was offered free of charge for all diabetic cats attending any veterinary practice in the UK from October 2003 till April 2011. Veterinary surgeons were asked to record clinical data about the patient, including age, breed, gender, current body weight, current administered insulin dose and whether they clinically suspected acromegaly/ hypersomatotropism. Diabetic cats were screened using serum total insulin-like growth factor-1, followed by further evaluation through pituitary imaging and/ or histopathology.

In total, 1221 diabetic cats were screened; 319 (26.1%) had a blood IGF-1 suggestive of hypersomatotropism. Of these cats a subset of 63 (20%) underwent pituitary imaging and 56/63 (89%) had a pituitary tumour on computed tomography; an additional three on magnetic resonance imaging and one on necropsy.  These data suggest a positive predictive value of serum IGF-1 for hypersomatotropism of 95%, suggesting the overall hypersomatotropism prevalence among UK diabetic cats to be 24.8%.

The paper also suggests that although great opportunities exist for comparative research between primary (type 2) diabetes in cats and humans, researchers should exercise caution in light of these new findings.

Stijn added: "The similarities between feline and human type 2 diabetes emphasise great opportunities for valuable comparative research benefiting all species into this major disease, which is fast becoming a global epidemic. However our latest research proves that there is a need for more regular hypersomatotropism screening, to identify the root cause of diabetes in domestic cats before samples are used, so as not to corrupt results."

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