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Ophthalmology => Diabetes Mellitus
Diabetes Mellitus
INTRODUCTION
Diabetes Mellitus, disease in which the pancreas produces little or no insulin, a hormone that helps the body's tissues absorb glucose (sugar) so it can be used as a source of energy. The condition may also develop if muscle and fat cells respond poorly to insulin. In people with diabetes, glucose levels build up in the blood and urine, causing excessive urination, thirst, hunger, and problems with fat and protein metabolism. Diabetes mellitus differs from the less common diabetes insipidus, which is caused by lack of the hormone vasopressin that controls the amount of urine secreted.
In the United States, about 16 million people suffer from diabetes mellitus, although only half of these individuals have been diagnosed. Every year, about 650,000 people learn they have the disease. Diabetes mellitus is the seventh leading cause of all deaths and the sixth leading cause of all deaths caused by disease.
Diabetes is most common in adults over 45 years of age; in people who are overweight or physically inactive; in individuals who have an immediate family member with diabetes; and in minority populations including African Americans, Hispanics, and Native Americans. The highest rate of diabetes in the world occurs in Native Americans. More women than men have been diagnosed with the disease.
TYPES OF DIABETES
In diabetes mellitus, without an appropriate level of insulin to help absorption glucose builds up in the blood because it cannot enter the cells. When the blood passes through the kidneys, organs that remove blood impurities, the kidneys cannot absorb all of the excess glucose. This excess glucose spills into the urine, accompanied by water and electrolytes-ions required by cells to regulate the electric charge and flow of water molecules across the cell membrane. This causes frequent urination to get rid of the additional water drawn into the urine; excessive thirst to trigger replacement of lost water; and hunger to replace the glucose lost in urination. Additional symptoms may include blurred vision, dramatic weight loss, irritability, weakness and fatigue, and nausea and vomiting.
Diabetes is classified into two types. In Type I, or insulin-dependent diabetes mellitus (IDDM), formerly called juvenile-onset diabetes, the body does not produce insulin or produces it only in very small quantities. Symptoms usually appear suddenly and in individuals under 20 years of age. Most cases occur before or around puberty. In the United States, about 5 to 10 percent of all diagnosed cases of diabetes, up to 800,000 persons, suffer from Type I diabetes. About 30,000 new cases are diagnosed every year.
Type I diabetes is considered an autoimmune disease because the immune system (system of organs, tissues, and cells that rid the body of disease-causing organisms or substances) attacks and destroys cells in the pancreas, known as beta cells, that produce insulin. Scientists believe that genetic and environmental factors, such as viruses or food proteins, may somehow trigger the immune system to destroy these cells.
Untreated Type I diabetes affects the metabolism of fat. Because the body cannot convert glucose into energy, it begins to break down stored fat for fuel. This produces increasing amounts of acidic compounds called ketone bodies in the blood, which interfere with respiration.
In Type II, or non-insulin-dependent diabetes mellitus (NIDDM), formerly called adult-onset diabetes, the body either makes insufficient amounts of insulin or is unable to use it. Symptoms characteristic of Type II diabetes include repeated infections or skin sores that heal slowly or not at all, generalized tiredness, tingling or numbness in the hands or feet, and itching.
The most common form of diabetes, Type II accounts for 90 to 95 percent of all cases of diagnosed diabetes in the United States. Each year 595,000 new cases are diagnosed. The onset of Type II diabetes usually occurs after the age of 40, and often after the age of 55. Because symptoms develop slowly, individuals with the disease may not immediately recognize that they are sick. Scientists believe that in some persons weight gain or obesity triggers diabetes-about 80 percent of diabetics with this form of the disease are overweight.
COMPLICATIONS
If left untreated, Type I diabetes can result in diabetic coma (a state of unconsciousness caused by extremely high levels of glucose in the blood) or death. In both Type I and Type II diabetes, blood sugar, blood pressure, and blood fats must be well-controlled to prevent possible development of blindness, kidney failure, and heart disease. Also, tiny blood vessels in the body may become blocked-a dangerous complication. When blood vessels of the eye are affected, it can result in retinopathy, the breakdown of the lining at the back of the eye. When the kidney is affected it is called nephropathy, the inability of the kidney to properly filter body toxins.
Diabetes mellitus may also cause loss of feeling, particularly in the lower legs. This numbness may prevent a person from feeling the pain or irritation of a break in the skin or foot infection until it is too late, possibly necessitating amputation of the foot or leg. Burning pain, sensitivity to touch, and coldness of the foot, conditions collectively known as neuropathy, can also occur.
Blockages of large blood vessels in diabetic persons can lead to many problems such as high blood pressure, heart attack, and stroke. Although these conditions also occur in nondiabetic individuals, they appear at a higher rate and often at a younger age in persons with diabetes. Other complications include higher risk pregnancies in diabetic women and a greater occurrence of dental disease.
DIAGNOSIS AND TREATMENT
Diabetes is detected by measuring the amount of glucose in the blood after the individual has fasted (abstained from food) for several hours, either overnight or several hours after breakfast. In some cases, physicians diagnose diabetes by administering an oral glucose tolerance test, the measurement of glucose levels before and after a specific amount of sugar is ingested. Another test being developed for Type I diabetes looks for specific antibodies (proteins of the immune system that attack foreign substances called antigens) present only in persons with diabetes. This test may detect Type I diabetes at an early stage, reducing the risk for complications from the disease.
Once diabetes is diagnosed, treatment consists of controlling the amount of glucose in the blood and preventing complications. Depending on the type of diabetes, this can be accomplished through regular physical exercise, a carefully controlled diet, and medication.
Individuals with Type I diabetes require insulin injections, often two to four times a day, to provide the body with the insulin it does not produce. The amount of insulin needed varies from person to person. Typically, several times a day, individuals with Type I diabetes measure the level of glucose in a drop of their blood obtained by pricking a fingertip. They can then adjust the amount of insulin injected, physical exercise, or food intake to maintain the blood sugar at a normal level. People with Type I diabetes must carefully control their diets by distributing meals and snacks throughout the day so the insulin supply is not overwhelmed and by eating foods that contain complex sugars, which break down slowly and cause a slower rise in blood sugar levels.
Although most persons with Type I diabetes strive to lower the amount of glucose in their blood, levels that are too low can also cause health problems. For example, low blood sugar levels can cause hypoglycemia, a condition characterized by shakiness, confusion, and anxiety. The treatment for hypoglycemia is to eat or drink something that contains sugar.
For persons with Type II diabetes, the basics of treatment are diet control, weight reduction, and exercise. Weight reduction appears to partially reverse the body's inability to use insulin. A person whose blood sugar level remains high may also require insulin injections. An oral sugar-lowering agent may be prescribed for persons who do not require insulin to control diabetes as well as for people who have trouble injecting themselves or whose diabetes is not controlled by insulin. About 40 percent of individuals with Type II diabetes require insulin while 49 percent take oral agents and 10 percent use diet and exercise alone. Moderate exercise, even ten minutes a day, helps people with Type II diabetes maintain a constant level of glucose in the blood and lose weight. This in turn may decrease the amount of medication required.
In 1983 a group of 1441 Type I diabetics from 13 to 39 years old participated in the Diabetes Control and Complications Trial (DCCT), the largest scientific study of diabetes treatment ever undertaken. The DCCT studied the potential for reducing diabetes-related complications, such as nerve or kidney disease or eye disorders, by having patients closely monitor their blood sugar levels several times a day, maintaining the levels as close to normal as possible. The results of the study, revealed in 1993, show a 50 to 75 percent reduction of diabetic complications in people who aggressively monitored and controlled their glucose levels. Although the study was performed on people with Type I diabetes, researchers believe the changes in treatment would also benefit people with Type II diabetes.
CURRENT RESEARCH
At present, no cure exists for diabetes and scientists are unsure of the exact cause. Researchers in England have identified up to 18 genes involved in Type I diabetes and are working to determine each gene's role in causing the disease. Other scientists hope to identify the environmental factors that trigger Type I diabetes. If they can determine what causes the immune system to attack the cells that produce insulin, they may discover how to prevent the condition from developing.
Other research focuses on transplanting a pancreas or its insulin-producing beta cells into a person with Type I diabetes to provide a natural source of insulin. Some patients who have received pancreas transplants have experienced considerable improvements in their health, but positive, long-term results with beta-cell transplants have not yet occurred. In both types of transplants recipients must take drugs that suppress their immune systems so the body will not reject the new pancreas or cells. These drugs can cause life-threatening side effects because the patient's body can no longer protect itself from other harmful substances. In most people with diabetes, these drugs pose a greater risk to health than living with diabetes. Scientists are also studying the development of an artificial pancreas and ways to genetically manipulate non-insulin-producing cells into making insulin.
In 1996 researchers discovered the first genetic link to Type II diabetes. The gene, which controls storage of sugar in muscle tissue, has been found in one-third of people with Type II diabetes and may indicate susceptibility to adult-onset diabetes. Recent findings indicate that a pair of genes causes a variation of Type II diabetes called maturity onset diabetes of the young (MODY), which develops in persons under the age of 25. While scientists do not yet understand how these genes cause the disease, the genes are known to be active in the liver, intestine, kidney, and pancreas.
New methods for accurately measuring blood glucose levels may improve the quality of life for many individuals with diabetes. Techniques being developed include the use of laser beams and infrared technology. For example, a tiny computer, using infrared light, will measure the blood sugar level and automatically deliver the reading to an insulin pump carried on the diabetic's body that will inject the appropriate amount of insulin. These pumps are available now, but they deliver insulin at preset times and rates.
Other advances include new drugs that control blood sugar in people with Type II diabetes. Examples are acarbose, which controls blood sugar by slowing the digestion of carbohydrates; metformin, which controls liver production of sugar, causes weight loss, and reduces total cholesterol; and troglitazone, which enhances the ability of cells to use glucose.
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