Glossary

Find definitions for thousands of medical terms, treatments, and tests -- even health-related abbreviations, prefixes, and suffixes.

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Deep vein thrombosis is a blood clot in a deep vein, usually in the legs. It can break loose and travel through the bloodstream to the lung. This is called pulmonary embolism and can be very dangerous.

Last Revised: October 9, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Jeffrey S. Ginsberg, MD - Hematology

Deep veins are the veins that are near the bones and surrounded by muscle. These veins lie deeper under the skin and return more blood to the heart than surface (superficial) veins.

Last Revised: December 28, 2011

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Jeffrey S. Ginsberg, MD - Hematology

Severe dehydration means:

  • Your mouth and eyes may be extremely dry.
  • You may pass little or no urine for 12 or more hours.
  • You may not feel alert or be able to think clearly.
  • You may be too weak or dizzy to stand.
  • You may pass out.

Severe dehydration is a medical emergency and requires emergency treatment. Call 911 or other emergency services immediately.

Moderate dehydration means:

  • You may be a lot more thirsty than usual.
  • Your mouth and eyes may be drier than usual.
  • Your urine may be much darker than usual.
  • You may pass little or no urine for 8 or more hours.
  • You may feel dizzy when you stand or sit up.

Mild dehydration means:

  • You may be more thirsty than usual.
  • Your urine may be darker than usual.

Mild to moderate dehydration is treated at home by drinking more fluids. Treatment for moderate to severe dehydration may include IV fluids and a stay in the hospital.

Dehydration is very dangerous for babies, small children, and older adults. It is most dangerous for newborns. Watch closely for early symptoms anytime there is an illness that causes a high fever, vomiting, or diarrhea.

Last Revised: May 2, 2011

Author: Healthwise Staff

Medical Review: William H. Blahd, Jr., MD, FACEP - Emergency Medicine & H. Michael O'Connor, MD - Emergency Medicine

Dementia is a loss of mental skills—such as memory, problem solving, and learning—that's bad enough to interfere with your daily life. It usually gets worse over time. But how long this takes is different for each person.

There are medicines you can take for dementia. They don't cure it, but they can slow it down for a while and make it easier to live with.

Last Revised: October 9, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Peter J. Whitehouse, MD - Neurology

Demyelination is a process in which the insulating coating (myelin sheath) around the nerve fibers is destroyed, slowing or halting the passage of nerve impulses. The myelin sheath allows nerve impulses to be sent between the brain, the spinal cord, and the nerves in the rest of the body smoothly and quickly.

Demyelination occurs in diseases such as multiple sclerosis (MS), Guillain-Barré syndrome, and chronic inflammatory demyelinating polyneuropathy (CIDP).

Last Revised: February 15, 2012

Author: Healthwise Staff

Medical Review: Adam Husney, MD - Family Medicine & Anne C. Poinier, MD - Internal Medicine & Barrie J. Hurwitz, MD - Neurology

Depression is an illness that makes you feel sad, lose interest in things you used to enjoy, withdraw from others, and have little energy. It's more than normal sadness, grief, or low energy. Most people get better with medicine, counseling, or a combination of the two.

After you have had an episode of depression, you are more likely to have it again.

Last Revised: January 11, 2013

Author: Healthwise Staff

Medical Review: Kathleen Romito, MD - Family Medicine & Lisa S. Weinstock, MD - Psychiatry

Dermatologists are medical doctors who specialize in diagnosing and treating diseases and conditions of the skin, hair, or nails, such as acne, psoriasis, warts, or skin cancer.

Dermatologists may prescribe medicines as well as perform surgery for skin disorders. They may specialize in treating specific age groups, such as a pediatric dermatologist, who only treats children.

Dermatologists can be board-certified through the Board of Dermatology, which is recognized by the American Board of Medical Specialties.

Last Revised: August 17, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & E. Gregory Thompson, MD - Internal Medicine

Diabetes is a condition in which sugar (glucose) remains in the blood rather than entering the body's cells to be used for energy. This results in high blood sugar. Over time, high blood sugar can damage many body systems.

Symptoms of diabetes include increased thirst and frequent urination (especially at night); unexplained increase in appetite; unexplained weight loss; fatigue; erection problems; blurred vision; and tingling, burning, or numbness in the hands or feet.

People who have high blood sugar over a long period of time are at increased risk for many serious health problems, including hardening of the arteries (atherosclerosis) and heart problems, eye problems that can lead to blindness, circulation and nerve problems, and kidney disease and kidney failure.

Women with diabetes and high blood sugar who become pregnant have an increased risk of miscarriage and birth defects.

Diabetes is treated with diet and lifestyle changes and with medicines. If blood sugar levels are kept within the recommended range, the risk for many complications from diabetes decreases.

Last Revised: September 20, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Jennifer Hone, MD - Endocrinology, Diabetes and Metabolism

Diabetic ketoacidosis (DKA) is a life-threatening blood chemical (electrolyte) imbalance that develops in a person with diabetes when the cells do not get the sugar (glucose) they need for energy. As a result, the body breaks down fat instead of glucose and produces and releases substances called ketones into the bloodstream.

People with type 1 diabetes and some people with type 2 diabetes are at risk for DKA if they do not take enough insulin, have a severe infection or other illness, or become severely dehydrated.

Symptoms of diabetic ketoacidosis include:

  • Flushed, hot, dry skin.
  • A strong, fruity breath odor.
  • Restlessness, drowsiness, or difficulty waking up. Young children may lack interest in their normal activities.
  • Rapid, deep breathing.
  • Loss of appetite, abdominal pain, and vomiting.
  • Confusion.

Severe diabetic ketoacidosis can cause difficulty breathing, brain swelling (cerebral edema), coma, or death.

Treatment involves giving insulin and fluids through a vein and closely monitoring and replacing electrolytes.

Last Revised: May 21, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & David C.W. Lau, MD, PhD, FRCPC - Endocrinology

Nephropathy means kidney disease or damage. Diabetic nephropathy is damage to your kidneys caused by diabetes.

The kidneys have many tiny blood vessels that filter waste from your blood. High blood sugar from diabetes can destroy these blood vessels. Over time, the kidney isn't able to do its job as well. Later it may stop working completely. This is called kidney failure.

Diabetic nephropathy is treated with medicine to slow or prevent further kidney damage. It can often be prevented by keeping blood sugar levels within a target range.

Last Revised: November 14, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Tushar J. Vachharajani, MD, FASN, FACP - Nephrology

Diabetic neuropathy is nerve damage caused by diabetes. Over time, high blood sugar can damage nerves throughout your body. Diabetic neuropathy can lead to serious foot problems and, in time, to problems like dizziness, diarrhea or constipation, sexual problems, bladder infections, and vision problems.

The older you get, and the longer you have diabetes, the more likely you are to have nerve damage. Controlling your blood sugar can help keep neuropathy from getting worse.

Last Revised: October 9, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Barrie J. Hurwitz, MD - Neurology

Retinopathy means disease of the retina, the nerve layer at the back of your eye. Diabetic retinopathy is related to prolonged high blood sugar, which damages blood vessels in the eyes. It can lead to poor vision or blindness.

Diabetic retinopathy usually gets worse over many years. People who have diabetes need regular eye exams so that this condition can be found early. Keeping your blood sugar and blood pressure under control can help protect your vision.

Last Revised: October 9, 2012

Author: Healthwise Staff

Medical Review: Adam Husney, MD - Family Medicine & Carol L. Karp, MD - Ophthalmology & Christopher J. Rudnisky, MD, MPH, FRCSC - Ophthalmology

Dialysis is a treatment for kidney failure that helps filter waste products from the blood when the kidneys are not working properly. The two main types of dialysis are hemodialysis and peritoneal dialysis.

  • Hemodialysis uses a man-made membrane (dialyzer) to filter wastes and remove extra fluid from the blood. It is usually done in a hospital or outpatient dialysis center 3 times a week. Some types of hemodialysis are done at home.
  • Peritoneal dialysis uses the lining of the abdomen (peritoneal membrane) and a solution (dialysate) to remove wastes and extra fluid from the body. Treatment can be done at home over several sessions each day or for several hours at night.

Last Revised: September 15, 2011

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Mitchell H. Rosner, MD - Nephrology

The diaphragm is a large sheet of muscle that separates the chest cavity (containing the lungs and heart) from the abdominal cavity (containing the digestive organs).

The diaphragm also serves as a muscle to help draw air into the lungs as a person breathes. It contracts to expand the lungs when breathing in (inhaling) and relaxes when breathing out (exhaling). If the diaphragm is not able to move as it should, breathing may become difficult.

Last Revised: November 29, 2011

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Ken Y. Yoneda, MD - Pulmonology

Diastolic pressure is the pressure of blood against the artery walls between heartbeats, when the heart is relaxed and filling with blood. It is the second or lower number in a blood pressure reading.

For example, if the diastolic pressure is 80 millimeters of mercury (mm Hg) and the systolic pressure is 120 mm Hg, the blood pressure is recorded as 120/80 and read as "120 over 80."

Last Revised: April 5, 2011

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Robert A. Kloner, MD, PhD - Cardiology

Severe trouble breathing means:

  • You cannot talk at all.
  • You have to work very hard to breathe.
  • You feel like you can't get enough air.
  • You do not feel alert or cannot think clearly.

Moderate trouble breathing means:

  • It's hard to talk in full sentences.
  • It's hard to breathe with activity.

Mild trouble breathing means:

  • You feel a little out of breath but can still talk.
  • It's becoming hard to breathe with activity.

Last Revised: December 21, 2011

Author: Healthwise Staff

Medical Review: William H. Blahd, Jr., MD, FACEP - Emergency Medicine & David Messenger, MD

Dilated cardiomyopathy is a serious problem that occurs when the heart muscle has become weak and enlarged. It does not have the strength to pump enough blood to the rest of the body.

Symptoms can come on gradually, over months or years. They also can start suddenly, such as after a viral infection or pregnancy. As the heart muscle weakens, a person may feel short of breath, especially when active. Other symptoms include fatigue, problems breathing while lying down, and swelling in the legs. These are symptoms of heart failure.

Most times, dilated cardiomyopathy is treated with several medicines. Changes in eating habits and lifestyle are also important in managing symptoms. These changes include limiting how much salt the person gets from food and drinks.

Last Revised: July 24, 2012

Author: Healthwise Staff

Medical Review: Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology & George Philippides, MD - Cardiology

A diuretic is a substance that removes water from the body by promoting urine formation and the loss of salt (sodium).

Caffeine and alcohol are common diuretics.

Diuretic medicines include furosemide, hydrochlorothiazide, metolazone, and spironolactone. These medicines may be used as part of treatment for conditions that cause swelling from water retention (edema), such as heart failure, hypertension, or liver or kidney disease.

Last Revised: October 23, 2012

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Robert A. Kloner, MD, PhD - Cardiology

Dizziness, or lightheadedness, is a feeling of unsteadiness. Dizziness can lead to feeling faint or to fainting (brief loss of consciousness).

Dizziness can be caused by many things, including stress and/or problems with brain functions.

Dizziness often goes away or improves after lying down. If it does not, it may be linked with conditions related to the inner ear or brain function.

Last Revised: January 2, 2013

Author: Healthwise Staff

Medical Review: William H. Blahd, Jr., MD, FACEP - Emergency Medicine & David Messenger, MD

A Doppler ultrasound (or duplex scanning) is a medical test that uses reflected sound waves to estimate the speed and direction of blood as it flows through a blood vessel. It helps doctors evaluate blood flow through arteries and veins.

Doppler ultrasound can be used to evaluate the vessels in several areas of the body. For example, a Doppler ultrasound test of the blood vessels in the neck (carotid ultrasound) can be done to estimate a person's risk of a stroke from blockage in those arteries. Renal ultrasound can help detect kidney problems. Lower extremity ultrasound can be used to detect a blood clot in the deep veins of the legs. A Doppler ultrasound also may be used to evaluate problems with the blood flow to the placenta and umbilical cord in a pregnant woman; problems with this blood flow may point to fetal distress.

Last Revised: November 29, 2012

Author: Healthwise Staff

Medical Review: Kathleen Romito, MD - Family Medicine & Howard Schaff, MD - Diagnostic Radiology

Down syndrome is a genetic condition caused by abnormal cell division in the egg, sperm, or fertilized egg. This results in an extra or irregular chromosome in some or all of the body's cells, causing varying levels of intellectual disability and physical problems.

Down syndrome is also called trisomy 21, for the specific chromosome that has the abnormality. A person with Down syndrome has three copies of chromosome 21. Normally, a person has two copies.

Down syndrome usually can be detected during pregnancy or soon after birth. Chromosome (karyotype) tests and how a baby looks can help make a diagnosis.

Babies usually have distinctive facial characteristics, such as upward-sloping eyes and a flattened nose. People with Down syndrome have an increased risk of being born with or developing health problems. For example, some babies with Down syndrome are born with heart, intestinal, ear, or respiratory defects. These health conditions often lead to other problems, such as respiratory infections, sleep apnea, or hearing problems. Other health issues, such as vision trouble or problems with thyroid function, can also develop.

Children with Down syndrome grow and develop more slowly than other children. But most are able to attend school, play sports, socialize, and enjoy active lifestyles. Unless their disabilities are severe, adults with Down syndrome can care for most of their own needs. Many people who have Down syndrome live into their 50s and some into their 60s or older.

Last Revised: July 20, 2011

Author: Healthwise Staff

Medical Review: Susan C. Kim, MD - Pediatrics & Louis Pellegrino, MD - Developmental Pediatrics

Dysfunctional uterine bleeding is a type of irregular bleeding from the uterus. For example, your periods may be less than 21 days or more than 35 days apart. They may last longer than 7 days, or they may be very heavy. This type of bleeding isn't serious, but it can be annoying and can disrupt your life.

Last Revised: October 9, 2012

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & Kirtly Jones, MD - Obstetrics and Gynecology