Endocrinology (diabetes mellitus) Flashcards
etiology, epidemiology, physiopathology
How frequent is diabetes mellitus in cats
Diabetes mellitus is considered the second most common endocrinopathy seen in cats after hyperthyroidism
- Estimated prevalence of 1 in 200 cats
- Prevalence of diabetes is increasing
- Among Burmese cats, prevalence is around 1 in 50 cats
Give a definition for diabetes mellitus
Diabetes is a complicated condition caused by either an absolute or a relative deficiency of insulin, which results in hyperglycemia and glycosuria
List risk factors for diabetes mellitus
Diabetes mellitus is most common in middle-aged and older cats
Neutered cats and males are at an increased risk
Obesity and other endocrine diseases such as hyperadrenocorticism and hypersomatotropism
- In these situations diabetes mellitus results from insulin resistance
Insulin resistance can also be seen with administration of some drugs (e.g. megestrol acetate, prednisolone)
Explain the normal actions of insulin
Insulin is produced by the beta cells in the islets of Langerhans in the pancreas and released into the circulation where it is transported to all the tissues of the body
Insulin has many roles in carbohydrates, fat and protein metabolism
- uptake of glucose, amino acids, fatty acids, potassium and magnesium by tissue cells
- hepatic glycogen and lipid synthesis
- inhibition of glycogenolysis and gluconeogenesis
Glucose and amino acids are potent insulin secretagogues in cats where a substantial proportion of glucose is derived from the metabolism of gluconeogenic amino acids
Explain the consequences of a lack of insulin
Diabetic cats have a relative or absolute deficiency in insulin resulting in impaired glucose uptake by tissue cells which causes hyperglycemia
As the cells are starved of glucose, they switch to using fat and protein as an energy source (triglycerides are oxidized to release fatty acids as an energy source, and protein catabolism is stimulated to release amino acids)
- this is facilated by the breakdown of body stores of fat and protein, resulting in weight loss and accumulation of toxic waste products, which can precipitate a diabetic crisis (ketoacidosis)
What is the main suspected cause of diabetes mellitus in cats
In the majority of cats, diabetes is associated with local pancreatic islet amyloidosis, and this is the most consistent histological change
Explain the process of pancreatic islet amyloidosis
The process is not related to systemic amyloidosis and to some extent is an age-related change in cats
The protein forming islet amyloid is called amylin which is a normal hormone co-secreted with insulin by beta cells
Important functions of amylin include:
- Suppression of post-prandial glucagon secretion
- Slowing gastric emptying rate thus reducing post-prandial hyperglycemia
- Mediates a cessation of satiety, reducing further food intake
Amyloid is deposited both within and around the beta-cells which is part of the cause of diabetes rather than merely a marker of beta- cells dysfunction
Explain the classification of diabetes mellitus
Type 1 diabetus mellitus
- Also referred as insulin dependent
- The beta-cells of the pancreas are destroyed by an immume-mediated process
- This is the most common form of diabetes in dogs but appears to be rare in cats
Type 2 diabetes mellitus
- Also referred as non-insulin dependent diabetes mellitus
- The majority of feline diabetes cases are strikingly similar to human type 2 DM
- Type 2 diabetic patients suffer from insufficient insulin seceretion by the pancreas AND peripheral insulin resistance impairing the action of insulin on tissue cells
- Histologically, the pancreas is characterised by amyloid deposition (from amylin)
Type 3 diabetes mellitus
- Diabetes is secondary to physiological or pathological situations causing insulin resistance
- In cats, this includes hyperadrenocorticism, acromegaly, administration of diabetogenic drugs (e.g., megestrol acetate, prednisolone), hyperprogesteronemia and severe obesity
- Pancreatitis (potentially a cause of reversible DM) and pancreatic neoplasia can affect the productionn of insulin
What are the clinical signs of diabetes mellitus
Hyperglycemia will result in glycosuria when the renal threshold is exceeded (>15 mmol/l or 252 mg/dl)
Glycosuria results in an osmotic diuresis causing polyuria and compensatory polydipsia
Weight loss and polyphagia are also frequently seen
The most common clinical signs seen in diabetic cats are weight loss, polyphagia, polydipsia and polyuria
Other clinical signs noted include:
- bacterial cystitis with dysuria and hematuria
- hepatomegaly
- poor hair coat
- in a small number of diabetic cats, peripheral neuropathies resulting in a classic plantigrade stance may be seen
- rarely cataracts and retinal abnormalities may be seen
Most diabetic cats will remain well in themselves except if ketoacidosis develops (extreme depression, vomiting, diarrhea, anorexia, dehydration, collapse, coma)
