Diabetes Mellitus

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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

Aetiology

Can be caused by

• Absolute deficiency of insulin due to degenerative changes in beta cells
• 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)
• Complication of pancreatic fibrosis
• Insulin binding antibodies, insulinase and plasma antagonists imbalance
• Chronic insulin resistance results in hyperinsulinism leading to islet exhaustion

Clinical signs

• 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

Pathology

• 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 is often opaque due to deposition of sorbitol causing it to swell (glucose is converted into sorbitol 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