Edema -Types, Pathophysiology and Causes

Edema

Presence of increased fluid in the interstitial space of the extracellular fluid compartment is known as edema. It is the accumulation of excessive fluid in the subcutaneous tissue. When edema results from lymphatic stasis, the term lymphoedema is used.

Types of edema fluid

a. Transudate

1. Protein-poor (<3 g/dL) and cell poor fluid
2. Produces dependent pitting edema and body cavity effusions
3. Associated with an alternation in starling pressure

b. Exudate

1. Protein-rich (>3 g/dL) and cell-rich (e.g., neutrophils) fluid
2. Produces swelling of tissue but no pitting edema

c. Lymphedema

1. Protein rich fluid
2. Nonpitting edema

Pathophysiology of Edema

1. Alteration in Starling pressure produces a transudate

a. Clinical examples of increased vascular hydrostatic pressure

i.    Pulmonary edema in left sided heart failure

ii.    Peripheral pitting edema in right sided heart failure

iii.    Portal hypertension in cirrhosis producing ascites

b. Clinical examples of decreased vascular plasma oncotic pressure (hypoalbuminemia)

i.    Malnutrition with decreased protein intake

ii.    Cirrhosis with decreased synthesis of albumin

iii.    Nephrotic syndrome with increased loss of protein in urine (>3.5 g/24 h)

iv.    Malabsorption with decreased reabsorption of protein

c. Renal retention of sodium and water

i.    Increased hydrostatic pressure (increased plasma volume)

ii.    Decreases oncotic pressure (dilutional effect on albumin)

iii.    Examples include acute renal failure, glomerulonephritis

2. Increased vascular permeability

3. Lymphatic obstruction produces lymphedema. Examples include:

i.    Lymphedema following modified radical mastectomy and radiation

ii.    Filariasis due to Wuchereria bancrofti

iii.    Scrotal and vulvar lymphedema due to lymphogranuloma venereum

iv.    Breast lymphedema (inflammatory carcinoma) due to blockage of subcutaneous lymphatic by malignant cells

4. Increased synthesis of extracellular matrix components (e.g. glycosaminoglycans)

• T-cell cytokines stimulate fibroblasts to synthesize glycosaminoglycans
• Examples include pretibial myxedema and exophthaloms in Graves’ disease

Causes

Generalized

Increased plasma hydrostatic pressure

• Congestive cardiac failure
• Vasodilatory drugs

Decreased plasma oncotic pressure

• Liver disease
• Renal disease, e.g. nephritic syndrome
• Malnutrition/absorption
  • Very common in the developing world

Impairment of lymphatic drainage

• Congenital deficiency of lymphatics

Increased capillary permeability

• Angio-oedema-anaphylaxis

Localized

Increased plasma hydrostatic pressure

Venous obstruction

Impairment of lymphatic drainage

Congenital

• Milroy’s disease
• Lymphoedema praecox
• Lymphoedema tarda

Acquired

• Malignant infiltration
• Infection, e.g. elephantiasis
  • Common in Africa
• Radiation
• Surgical damage

Increased capillary permeability

• Local infection
• Trauma