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Tuesday, October 03, 2006

Diagnosis and classification DM: New criteria.

New recommendations for the classification and diagnosis of diabetes mellitus include the preferred use of the terms "type 1" and "type 2" instead of "IDDM" and "NIDDM" to designate the two major types of diabetes mellitus; simplification of the diagnostic criteria for diabetes mellitus to two abnormal fasting plasma determinations; and a lower cutoff for fasting plasma glucose (126 mg per dL [7 mmol per L] or higher) to confirm the diagnosis of diabetes mellitus.

These changes provide an easier and more reliable means of diagnosing persons at risk of complications from hyperglycemia. Currently, only one half of the people who have diabetes mellitus have been diagnosed. Screening for diabetes mellitus should begin at 45 years of age and should be repeated every three years in persons without risk factors, and should begin earlier and be repeated more often in those with risk factors.

Risk factors include obesity, first-degree relatives with diabetes mellitus, hypertension, hypertriglyceridemia or previous evidence of impaired glucose homeostasis. Earlier detection of diabetes mellitus may lead to tighter control of blood glucose levels and a reduction in the severity of complications associated with this disease.

Diabetes mellitus is a group of metabolic disorders with one common manifestation: hyperglycemia. Chronic hyperglycemia causes damage to the eyes, kidneys, nerves, heart and blood vessels. The etiology and pathophysiology leading to the hyperglycemia, however, are markedly different among patients with diabetes mellitus, dictating different prevention strategies, diagnostic screening methods and treatments. The adverse impact of hyperglycemia and the rationale for aggressive treatment have recently been reviewed.

Previous Classification
Diabetes mellitus that is characterized by absolute insulin deficiency and acute onset, usually before 25 years of age, should now be referred to as type 1 (not type I, IDDM or juvenile) diabetes mellitus.

In 1979, the National Diabetes Data Group produced a consensus document standardizing the nomenclature and definitions for diabetes mellitus. This document was endorsed one year later by WHO. The two major types of diabetes mellitus were given names descriptive of their clinical presentation: "insulin-dependent diabetes mellitus" (IDDM) and "noninsulin-dependent diabetes mellitus" (NIDDM).
However, as treatment recommendations evolved, correct classification of the type of diabetes mellitus became confusing. For example, it was difficult to correctly classify persons with NIDDM who were being treated with insulin. This confusion led to the incorrect classification of a large number of patients with diabetes mellitus, complicating epidemiologic evaluation and clinical management. The discovery of other types of diabetes with specific pathophysiology that did not fit into this classification system further complicated the situation. These difficulties, along with new insights into the mechanisms of diabetes mellitus, provided a major impetus for the development of a new classification system.
The National Diabetes Data Group also established the oral glucose tolerance test (using a glucose load of 75 g) as the preferred diagnostic test for diabetes mellitus. However, this test has poor reproducibility, lacks physiologic relevance and is a weaker indicator of long-term complications compared with other measures of hyperglycemia.6 Furthermore, many high-risk patients are unwilling to undergo this time-consuming test on a repeat basis. The new diagnostic criteria also address this issue.

Changes in the Classification System
The new classification system identifies four types of diabetes mellitus: type 1, type 2, "other specific types" and gestational diabetes. Arabic numerals are specifically used in the new system to minimize the occasional confusion of type "II" as the number "11." Each of the types of diabetes mellitus identified extends across a clinical continuum of hyperglycemia and insulin requirements.
Any patient with two fasting plasma glucose levels of 126 mg per dL (7.0 mmol per L) or greater is considered to have diabetes mellitus.
Type 1 diabetes mellitus (formerly called type I, IDDM or juvenile diabetes) is characterized by beta cell destruction caused by an autoimmune process, usually leading to absolute insulin deficiency.
the onset is usually acute, developing over a period of a few days to weeks. Over 95 percent of persons with type 1 diabetes mellitus develop the disease before the age of 25, with an equal incidence in both sexes and an increased prevalence in the white population. A family history of type 1 diabetes mellitus, gluten enteropathy (celiac disease) or other endocrine disease is often found.
Most of these patients have the "immune-mediated form" of type 1 diabetes mellitus with islet cell antibodies and often have other autoimmune disorders such as Hashimoto's thyroiditis, Addison's disease, vitiligo or pernicious anemia.
A few patients, usually those of African or Asian origin, have no antibodies but have a similar clinical presentation; consequently, they are included in this classification and their disease is called the "idiopathic form" of type 1 diabetes mellitus.

Type 2 diabetes mellitus (formerly called NIDDM, type II or adult-onset) is characterized by insulin resistance in peripheral tissue and an insulin secretory defect of the beta cell.2,7 This is the most common form of diabetes mellitus and is highly associated with a family history of diabetes, older age, obesity and lack of exercise. It is more common in women, especially women with a history of gestational diabetes, and in blacks, Hispanics and Native Americans. Insulin resistance and hyperinsulinemia eventually lead to impaired glucose tolerance. Defective beta cells become exhausted, further fueling the cycle of glucose intolerance and hyperglycemia. The etiology of type 2 diabetes mellitus is multifactorial and probably genetically based, but it also has strong behavioral components.
Types of diabetes mellitus of various known etiologies are grouped together to form the classification called "other specific types." This group includes persons with genetic defects of beta-cell function (this type of diabetes was formerly called MODY or maturity-onset diabetes in youth) or with defects of insulin action; persons with diseases of the exocrine pancreas, such as pancreatitis or cystic fibrosis; persons with dysfunction associated with other endocrinopathies (e.g., acromegaly); and persons with pancreatic dysfunction caused by drugs, chemicals or infections.

TABLE 1 Etiologic Classifications of Diabetes Mellitus
Type 1 diabetes mellitus*
Type 2 diabetes mellitus*
Other specific types:
Genetic defects of beta-cell function
Genetic defects in insulin action
Diseases of the exocrine pancreas
Pancreatitis
Trauma/pancreatectomy
Neoplasia
Cystic fibrosis
Hemochromatosis
Others
Endocrinopathies
Acromegaly
Cushing's syndrome
Glucagonoma
Pheochromocytoma
Hyperthyroidism
Somatostatinoma
Aldosteronoma
Others
Drug- or chemical-induced
Vacor†
Pentamidine
Nicotinic acid
Glucocorticoids
Thyroid hormone
Diazoxide
Beta-adrenergic agonists
Thiazides
Phenytoin
Alfa-interferon
Others
Infections
Congenital rubella
Cytomegalovirus
Others
Uncommon forms of immune- mediated diabetes
Other genetic syndromes sometimes associated with diabetes
Down syndrome
Klinefelter's syndrome
Turner's syndrome
Wolfram syndrome
Friedreich's ataxia
Huntington's chorea
Lawrence-Moon Beidel syndrome
Myotonic dystrophy
Porphyria
Prader-Willi syndrome

Final Comment
The changes recommended by the expert committee for the diagnosis of diabetes mellitus should prove beneficial to patients. Measurement of fasting plasma glucose levels should be more acceptable to patients than the oral glucose tolerance test and can be readily incorporated with fasting lipid determinations. Identifying asymptomatic persons earlier in the disease process will allow earlier institution of lifestyle changes and medical therapy that may decrease the complications of hyperglycemia. The National Diabetes Data Group emphasizes that these changes in diagnostic criteria have not changed the treatment goals in patients with diabetes mellitus. These goals include maintaining a fasting plasma glucose level of less than 120 mg per dL (6.65 mmol per L) and a glucose hemoglobin measurement of less than 7.0 percent.
Figure 1 adapted with permission from Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Diabetes Care 1997;20: 1183-97.

By: JENNIFER MAYFIELD, M.D., M.P.H.

posted by ummu Fauzan @ 8:00 AM

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