Edema is swelling due to an accumulation of excess fluid. Your body has set fluid levels and will restore itself to its usual state within 48 hours of taking in extra water under normal circumstances. There are many causes and subtypes of edema including hypertensive, exercise, high altitude, tropical, medication and idiopathic cyclic edema. Idiopathic Cyclic Edema
This is one subtype primarily occurring in young menstruating women in which large amounts of tissue swelling occurs in the legs and abdomen after sitting or standing, and swelling of the face and eyelids upon lying down. It is thought to be a problem of leakage of blood fluids from capillaries into fat and skin tissue especially when gravity (standing up) is added to the pressure in the vascular system. It results in large weight changes from morning to evening. Sometimes the condition is called idiopathic orthostatic (standing upright) edema or just idiopathic edema. Other names include fluid retention syndrome and cyclical edema.

This condition can result in moderate discomfort in any area of excess fluid accumulation. Carpal tunnel syndrome, diffuse aching, morning stiffness and muscle/bone pains as well as headaches often accompany the swelling. It can also masquerade as premenstrual syndrome or make existing premenstrual syndrome worse. It exacerbates the swelling, abdominal bloating and general physical discomfort but it does not usually cause irritability or depressive symptoms as does classic PMS. Sometimes the syndrome can occur in women with eating disorders who are taking diuretics or even laxatives in order to lose weight.

Swelling in both legs can have many other possible causes

• Prolonged standing or sitting, especially in hot weather, may cause excess fluid accumulation in the feet, ankles and lower legs.
• Venous insufficiency is a common problem of the weakened valves in the veins of the legs. This leads to varicose veins and build up of fluid.
• Severe chronic lung disease such as emphysema or chronic bronchitis increase the pressure in the blood vessels to the lungs. This pressure backs up in the right side of the heart and the higher pressure causes swelling in the legs and feet.
• Congestive heart failure due to decreased pumping action of the heart muscle causes fluid buildup in the lungs and other parts of the body. The swelling is often most visible in the feet and ankles.
• Pregnancy with leg edema occurs because the pregnant uterus puts pressure on the vena cava, a major blood vessel that returns blood to the heart from the legs. Fluid retention of pregancy also might be caused by a more serious condition called preeclampsia.
• Low protein levels in the blood that can be seen in malnutrition, kidney and liver disease. The proteins in the blood help hold salt and water inside the blood vessels so fluid does not leak out into the tissues. If albumin (the most abundant blood protein) gets too low, edema occurs especially in the feet, ankles and lower legs.

Diagnosis
To check for edema that is not obvious, you can gently press your thumb over the foot, ankle or leg with slow, steady pressure. If edema is present, an indentation will show on the skin. A professional evaluation to determine the cause of leg swelling is needed. If both legs are swollen, your doctor will inquire about other symptoms and perform a physical examination. A urine test will show whether you are losing protein from the kidneys. Blood tests, a chest X-ray and an electrocardiogram (ECG) may be ordered.

Prevention
Prevention of edema means preventing the cause. Smoking is the No. 1 cause of chronic lung disease. Congestive heart failure most often is due to coronary artery disease and high blood pressure. To avoid leg swelling on long trips or due to long hours at a desk job, stand up and walk around often; ideally you should get up once per hour. If not possible, then exercise your feet and lower legs while sitting. This will help the veins move blood back toward the heart.

When you repeatedly take laxatives, diuretics or vomit, your body will adapt to being constantly dehydrated by learning to retain more fluid than usual. When you stop these behaviors and start to take a normal diet, your body may continue to retain fluids until it learns that adequate fluid will be available, then it will release the extra fluid. People who abuse laxatives or vomit regularly are at the greatest risk for alternating between dehydration and edema.

It may take from 2 to 6 weeks following long term dehydration for your body to get used to being normally hydrated again and flush out the extra fluid it has been retaining.

Treatment
Treatment focuses on correcting the underlying cause of the fluid accumulation. In addition, a low-salt diet and avoiding excess fluid intake usually helps. If you are not short of breath, elevation of the legs above the level of your heart will also keep swelling down. A low dose of a diuretic (water pill) used sparingly might be added in some cases.

For swollen ankles and feet caused by pregnancy from the enlarged uterus pushing on the vena cava, elevation of the legs and not lying on your back (either side) helps blood flow and decreases swelling.

Most patients with mild leg edema due to varicose veins can be treated with periodic leg elevation and support (compression) stockings. Sometimes surgery is needed to improve the flow of blood through the leg veins.

Also, no matter what the underlying cause of edema, any swollen area of the body should be protected from pressure, injury and extreme temperatures. The skin over swollen legs becomes more fragile over time. Cuts, scrapes and burns take much longer to heal and are more prone to infection when skin has edema underneath.

When to seek help
Call your doctor immediately if you have pain, redness or heat in the swollen area, an open sore, shortness of breath or swelling of only one limb. If the swelling has never happened before and it persists for more than a couple days, call your doctor's office for advice.

Prognosis
The prognosis for edema of the legs depends on the cause. For most people with edema, the prognosis is excellent.