Why are my legs and ankles swollen?

DEAR DOCTOR K:

Why are my legs and ankles swollen?

DEAR READER:

Swelling of the legs from a buildup of extra fluid is known as edema. In addition to the swelling, the skin above the swollen area is stretched and shiny. Your doctor can easily check for edema by gently pressing a finger over your foot, ankle or leg with slow, steady pressure. If you have edema, you will see an indentation where the doctor pressed.

Swelling of the legs and ankles is usually not serious. However, it can be caused by diseases of the heart, lungs, liver and kidney.

Where does the extra fluid come from? About 60 percent of our body weight is from water. The water is in three “spaces.” Most is in the space inside each cell. Some is in the space between our cells. The rest is in the space inside our blood vessels and a few other locations. Water passes back and forth between these spaces.

The presence of edema means that there is more fluid than normal in the space between the cells. Usually, this extra fluid comes from the fluid inside the blood vessels.

Edema of any cause is often worst in the legs and ankles. When we’re sitting or standing, gravity pulls the water inside blood vessels downward. That raises pressure inside the blood vessels, which pushes water out into the space between the cells.

The two most common causes of leg and ankle swelling are:

  1. prolonged standing or sitting, especially in hot weather;
  2. weakness of tiny valves inside the veins of the legs.

The weakened valves make it more difficult for the veins to pump blood back to the heart. As a result, water leaks out of the veins and into the space between the cells.

Pregnancy can cause edema in the legs. The baby and uterus press on the veins carrying blood from the legs to the heart. Like weakened valves in leg veins, this causes water to leak out of the veins and into the space between the cells. Fluid retention during pregnancy also can be caused by a more serious condition called pre-eclampsia.

One serious cause of leg and ankle swelling in adults is congestive heart failure. When the heart is not pumping efficiently, some blood pools in the veins of the legs (again, because of gravity), and water leaks into the space between the cells.

Another cause is low protein levels in the blood, often the result of malnutrition or kidney and liver disease. This produces swelling not only in the legs and ankles but everywhere; puffy eyes and face are common.

A more serious cause of swelling in the legs and ankles, and in the face, is a seriously underactive thyroid gland.

In tomorrow’s column we’ll discuss what your doctor should do to diagnose the cause of your edema, and what you and your doctor should do to treat it.