Edema and Its Causes

Overview

Edema is a common symptom that almost everyone experiences at least once, and it refers to a condition in which the body swells. It means an abnormal accumulation of fluid between the body's cells. When the entire body swells, it is called generalized edema, and when only a specific area swells, it is called localized edema. About 70% of the human body is made up of water, of which 2/3 is inside cells and the remaining 1/3 is outside cells. Of the extracellular fluid, 25% is in the blood and 75% is in the spaces between cells as interstitial fluid. Water can move between the blood and the interstitial space. When the pressure inside the blood vessels is high or the osmotic pressure inside the blood drops, water in the blood moves into the interstitial space between cells, causing edema.

Causes

In general, generalized edema is caused by systemic diseases such as heart failure, cirrhosis, and kidney failure, whereas localized edema is mainly caused by abnormalities in the vascular system such as the arteries, veins, and lymphatic vessels.

1. Congestive heart failure This refers to a disease in which the heart's ability to pump blood out is reduced. It is the most representative heart disease that causes edema. When congestive heart failure occurs, the heart's pumping function declines, reducing the amount of blood flowing through the bloodstream, and the kidneys reabsorb water and sodium, preventing water from leaving the body. When water reabsorbed into the blood vessels escapes into the interstitial space between cells, generalized edema and pulmonary edema occur.

2. Cirrhosis This means that chronic inflammation causes normal liver tissue to become hard, fibrotic tissue, leading to decreased liver function. As the liver becomes hardened, blood circulation into and out of the liver becomes poor, causing portal hypertension in the portal vein that flows to the liver. In addition, as the production of albumin, a protein made by the liver, decreases, the concentration of albumin in the blood also decreases, weakening osmotic pressure. When osmotic pressure is weak, the ability to retain water in the blood vessels is reduced, so water leaks into the interstitial space between cells surrounding the blood vessels, causing edema. For this reason, patients with cirrhosis often develop generalized edema along with ascites.

3. Nephrotic syndrome Nephrotic syndrome is one of the rare causes of edema and is a condition characterized by excessive proteinuria accompanied by edema, hypoalbuminemia in the blood, and hyperlipidemia in which lipids accumulate in the blood. In the past, edema in nephrotic syndrome was thought to be caused by reduced osmotic pressure, but recently it is considered to result from water retention due to excess sodium.

4. Hypothyroidism Edema caused by hypothyroidism is the so-called myxedema, a special type of edema in which proteins containing large amounts of hyaluronic acid accumulate in the skin. It mainly occurs on the front of the shins and is characterized by firm swelling that does not pit when pressed. If the edema worsens, it can spread to a wider area, extending to the face, eyes, hands, and feet.

5. Hypoalbuminemia When hypoalbuminemia occurs, osmotic pressure decreases, making it impossible to retain salt and water in the blood vessels, which reduces circulating blood volume. As compensation, salt and water are reabsorbed, but because osmotic pressure is reduced, they leak out of the blood vessels and cause edema.

6. Drug-induced edema Many drugs can cause edema. Drug-induced edema usually occurs on the tops of the feet and around the ankles. Some drugs constrict the blood vessels in the kidneys and increase sodium reabsorption, and representative drugs include anti-inflammatory pain relievers, steroids, and calcium channel blocker antihypertensives. Drug-induced edema appears when a drug is used excessively or for a long time.

7. Idiopathic edema Idiopathic edema refers to edema with no identified cause. It is more common in women and refers to edema that occurs periodically regardless of the menstrual cycle.

8. Premenstrual edema Edema that occurs in relation to the menstrual cycle is called premenstrual edema. Excess estrogen stimulation causes secondary sodium and water retention, leading to edema. In addition to edema, it is accompanied by various other symptoms. It differs from idiopathic edema in that it occurs periodically.

9. Venous insufficiency Venous insufficiency is edema caused by reduced venous function. When a vein is blocked, as in deep vein thrombosis, capillary pressure increases and water moves from the blood vessels into the interstitial space, causing edema.

10. Lymphedema Lymphedema is a condition in which protein-rich fluid accumulates excessively in a localized area due to damage to the lymphatic system. It mainly occurs because damage to the lymph nodes after cancer or cancer treatment disrupts the flow of lymph, causing swelling in the affected area. In some countries in Africa and Southwest Asia, lymphedema can occur due to a parasitic infection called filariasis, in which parasites live in the lymphatic vessels.

11. Lipedema Lipedema refers to an abnormal accumulation of subcutaneous fat. Female hormones are involved, and it mainly occurs between the pelvis and the ankles. Excess production of fat cells under the skin causes changes in small blood vessel structures, leading to edema. In patients with lipedema, it begins within 1 to 2 years after puberty and persists, with a feeling of heaviness and pain in the legs, thighs, and pelvis. A characteristic feature is the symmetrical accumulation of subcutaneous fat around both ankles. In the early stage, the skin surface feels like a poorly defined mass, and later it appears as orange-colored accumulated fat.

12. Senile leg edema Senile leg edema refers to edema that occurs as people age, due to decreased skin elasticity and muscle strength, which causes blood to pool in the legs and circulation to become poor. Swelling below the knees and a feeling of heaviness are commonly reported.

So far, I have explained edema and its causes. In the next part, we will look at the treatment of edema.

Source: Korea Disease Control and Prevention Agency, National Health Information Portal