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Distinguish among the major types of diabetes mellitus (DM).
DM is the presence of elevated plasma glucose under fasting conditions. Type I, or insulin-dependent DM (IDDM), occurs in about 10% of all diabetics in the Western world (Table 29.1). Classically, this type of DM presents in child-hood or early adolescence; however, it can manifest at any age. The presentation is usually abrupt, with onset of symptoms secondary to severe insulin insufficiency. Type I DM patients are prone to ketosis and are usually thin. The pathogenesis of IDDM is thought to involve certain histocompatibility locus antigens (HLA) on chromosome 6. In the most common form of IDDM (type IA), environ-mental factors, such as viral infections, are postulated to combine with genetic factors to cause cell-mediated autoimmune destruction of pancreatic beta cells. The sec-ond type of IDDM (type IB) is found in about 10% of all IDDM patients and is thought to involve primary auto-immune damage. This type of IDDM is associated with other autoimmune endocrinopathies such as Hashimoto’s thyroiditis, Graves’ disease, and other nonendocrine autoimmune disorders.
Type II DM, or non-insulin-dependent DM (NIDDM), occurs in 90% of all diabetics. However, the name may be misleading since some patients may require insulin to cor-rect persistent fasting hyperglycemia if diet and oral agents fail to do so. The requirement of insulin for glucose control does not distinguish between IDDM and NIDDM. Although these patients are not ketosis prone, they still may develop ketosis under circumstances of severe stress. The pathogenesis of NIDDM is also thought to involve genetic factors as expressed by a strong familial pattern for NIDDM. There appears to be a difference between obese and non-obese NIDDM patients. Sixty to eighty percent of NIDDM patients have insulin resistance resulting from weight gain and obesity. In most patients, a diagnosis of NIDDM is made during middle age. In a subclass of patients, DM presents during childhood or adolescence, which is known as maturity onset-type diabetes of the young (MODY). This has an established autosomal dominant inheritance pattern. Gestational DM (GDM) is defined as the onset of glucose intolerance during pregnancy. About 2% of all pregnancies are associated with GDM, which is related to an increase in perinatal morbid-ity and mortality. Although most patients return to a state of normal glucose tolerance following parturition, about 60% will develop DM within 15 years.
Other forms of DM include malnutrition-related DM, which is a non-ketosis-prone form associated with severe protein malnutrition and emaciation. Most cases require insulin for preservation of life. DM may also be secondary to other endocrine diseases (e.g., Cushing syndrome), drug administration (e.g., antihypertensive drugs, estro-gens), and many genetic syndromes. DM may also result from severe pancreatic disease or resection of pancreatic tissue.
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