Diabetes mellitus

Clinically significant glucose intolerance
Chronic disease caused by absolute or relevant deficiency of insulin and therefore disorders of carbohydrate metabolism
Occurs in most species, most commonly in dog and cat
Predisposed to pancreatitis and may also have pancreatic insufficiency
Persistent increase in glucagon may cause hyperglycaemia
More common in mature dogs, twice as common in females than in males

Can be caused by

Absolute deficiency of insulin due to degenerative changes in beta cells (Miniature poodles, Dachsunds,Terriers seem to be predisposed)
Antagonism of insulin by hormones from the adrenal and thyroid glands, anterior pituitary causing high levels of blood glucose (e.g. progesterone may initiate postoestrus DM in the bitch, hyperadrenocorticism)
Complication of pancreatic fibrosis
Immune-mediated disease
Insulin binding antibodies, insulinase and plasma antagonists imbalance
Chronic insulin resistance (due to excessive food intake and down regulation of receptors) results in hyperinsulinism leading to islet exhaustion
Glycogenosis and hydropic degeneration, amyloidosis (esp. cats)
Other factors, eg. stress, viral infection, genetic factors

Hyperglycaemia
Polyuria
Polydypsia
Polyphagia
Weight loss
Muscle wasting (but some animals may present obese)
Hepatomegaly
Cataracts (dogs)
Later stages when becoming ketoacidotic
- Dehydration
- Depression
- Inappetance
- Vomiting
- Diarrhoea
- Ketotic breath
Reduced cardiac output (due to loss of water and sodium), reduced blood pressure and renal flow causing circulatory collapse, coma and death

Pancreas appers normal or reduced in size due to fibrosis
In cats, amyloidosis is sometimes present in the islets
Fatty change is consistently present in the liver and kidneys
The lens in the eye of the dog is often opaque due to deposition of sorbitol and fructose causing it to swell as the are not freely permeable (glucose is converted into sorbitol and fructose once the glycolytic pathway is saturated)
In immune-mediated isletitis - progressive lymphoplasmacytic infiltration and selective destruction of islet cells
Possible vacuolation of islet cells and epithelium of small ducts

where there is insufficient insulin or a decrease in number of insulin receptors in cells
seen mostly in dogs
produces a markedly fatty liver due to release of fat from the fat stores for use as an energy source

Diabetes Mellitus