mellitus: complications

Chapter 52 Diabetes mellitus: complications

Questions

What are the acute complications of diabetes mellitus?

What are the long-term complications?

What infectious complications of diabetes mellitus can occur?

For ease of discussion, complications are divided into three groups: acute, chronic and infectious.

Acute complications

Diabetic ketoacidosis. Lipolysis is a characteristic of insulin lack (Ch. 51). Released free fatty acids are converted in the liver to ketone bodies (e.g. acetoacetate, acetone and 3-hydroxybutyrate). These substances are acidic and release hydrogen ions, causing metabolic acidosis. The combination of excess ketone bodies (ketosis) and acidosis is called ketoacidosis, and is usually seen in type 1 diabetes.

Hyperosmolar non-ketotic syndrome. This condition typically occurs in older patients with type 2 diabetes. It is characterized by hyperglycaemia and dehydration. A typical scenario is a patient who does not drink enough water to compensate for the urinary losses through osmotic diuresis; the consequence is a rise in serum osmolality. Ketoacidosis is minimal or absent.

Lactic acidosis. Rarely, diabetics present with lactic acidosis. The prognosis is poor.

Hypoglycaemia. This is a complication seen in treated diabetics who take insulin (or occasionally other hypoglycaemic agents) in excess of requirements. The resultant fall in blood glucose can cause mental symptoms, hunger, palpitations, sweating, abnormalities of behaviour and convulsions. In severe hypoglycaemia, patients may present with coma, but this must not be confused with the coma caused by ketoacidosis in untreated diabetes.

Chronic complications

Diabetes is one of the most important causes of morbidity and mortality in the industrialized world, largely through its effects on blood vessels (atheroma and microangiopathy). Coronary artery disease, cerebrovascular events, peripheral vascular disease and renal failure are common in diabetics; approximately 80% of adult diabetics die from cardiovascular disease. Furthermore, long-standing diabetes mellitus, especially type 1, is often complicated by serious retinal disease. Most of these complications appear to be directly related to hyperglycaemia, and good control of blood glucose levels delays their development. The mechanisms linking hyperglycaemia to these complications are only partially understood, but the following appear to be important.

Glycosylation of proteins. Glucose can bind to proteins by chemical reactions that do not depend on enzymes (non-enzymatic glycosylation), and this process may be important in the pathogenesis of diabetic complications (Fig. 3.52.1). The amount of non-enzymatically glycosylated protein in the body is directly proportional to the level of blood glucose. This phenomenon is exploited in the glycosylated haemoglobin (HbA1c) test, in which the level of circulating HbA1c is used as a measure of the average blood glucose over the previous few weeks, and thus as an indication of the control of blood glucose achieved by a diabetic patient.

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