Chapter 113: Diabetes Mellitus

INTRODUCTION

Diabetes mellitus is an endocrinologic disorder in which carbohydrate metabolism is compromised by either reduced insulin production or sensitivity, resulting in hyperglycemia. In 2013 there were 382 million estimated cases of diabetes worldwide.

Type 1 diabetes, also known as insulin-dependent diabetes mellitus (IDDM), accounts for 5%–10% of all cases. It is a chronic autoimmune disorder in which the beta cells of the pancreas are affected, resulting in the cessation of insulin production. Exogenous insulin is the primary therapy for type 1 diabetes. Onset is typically acute. Initial symptoms due to hyperglycemia may include polydipsia, polyuria, hyperphagia, weight loss, fatigue, and blurred vision. If untreated, coma from ketoacidosis may be the diagnostic presentation.

Type 2 diabetes starts as insulin resistance. Insulin production may initially increase in an attempt to overcome this resistance, but eventually it is inadequate. Therapy may include weight reduction via exercise and diet, oral hypoglycemic medications, and exogenous insulin.

The diagnosis of diabetes mellitus requires fulfilling at least one of the following criteria:

• Fasting blood glucose > 125 mg/dL on more than one occasion

• Random blood glucose > 199 mg/dL along with symptoms of polyuria, polydipsia, or weight loss

• 75 g glucose tolerance test with a 2 h value > 199 mg/dL

• HA_1C > 6.4 %

Prolonged hyperglycemia leads to complications associated with diabetes in two forms: microvascular and macrovascular disease processes. Microvascular complications include retinopathy, nephropathy, and neuropathy. Peripheral sensory neuropathy may lead to a propensity for foot wounds. Autonomic neuropathy can cause hemodynamic fluctuations, gastroparesis, and silent cardiac ischemia. Macrovascular disease processes associated with diabetes include coronary artery disease, cerebrovascular disease, and peripheral vascular disease. Hypertension and dyslipidemia are comorbidities that frequent diabetics.

Nonenzymatic glycosylation of hemoglobin by plasma glucose can be quantified via the blood test hemoglobin A1C (HA_1C). The lifespan of a red blood cell is approximately 90 days; thus, HA_1C levels give a 90 day average of glycemic control. Higher HA_1C levels correlate with a higher average blood sugar and thus more hyperglycemia complications (Table 113-1).

1. Oral hypoglycemics—There are seven main classes of oral hypoglycemic medications (Table 113-2). These medications are prescribed to type 2 diabetics, and not useful for patients who no longer make insulin. They may be used in combination and with or without exogenous insulin administration.

2. Insulin—Insulin is a hormone made in the β-cells of the islets of Langerhans in the pancreas. It is released into the blood stream in response to an elevation in plasma glucose. Insulin facilitates a number of anabolic processes, including glucose uptake into ...