One function of the lymphatic system is to return excess fluid and protein from interstitial spaces to the blood vascular system. Because lymphatic vessels often lack a basement membrane, they can resorb molecules too large for venous uptake. Mechanisms of clinical edema include increased arteriovenous capillary filtration and reduced interstitial fluid absorption. Causes of increased capillary filtration include increased hydrostatic pressure in capillaries, decreased tissue pressure, and increased membrane permeability. Reduced interstitial fluid resorption can be caused by decreased plasma oncotic pressure, increased oncotic pressure of tissue fluid, and lymphatic obstruction.
Anatomy of the lymph system showing the lymph vessels and lymph organs, including the lymph nodes, tonsils, thymus, spleen, and bone marrow. Lymph (clear fluid) and lymphocytes travel through the lymph vessels and into the lymph nodes where the lymphocytes destroy harmful substances. The lymph enters the blood through a large vein near the heart.
The onset of secondary lymphedema is often insidious. However, it may be suddenly provoked by local inflammation from causes such as infection or limb injury. Therefore, patients should be evaluated for evidence of cellulitis. Classically, lymphedema is characterized by nonpitting swelling of an extremity, usually with involvement of the digits. Early stages of lymphedema manifest with pitting edema until fibrosis develops. The distribution of the swelling may be restricted only in the proximal or distal portion of the limb. Lymphedema may also predispose to recurrent skin infections.
Lymphedema can and does occur in the trunk, in addition to the limbs. For example, radiation therapy to the chest wall is associated with the development of edema specifically in the irradiated breast.[6,7]
Patients with lymphedema may report a wide variety of complaints, including heaviness or fullness related to the weight of the limb, a tight sensation of the skin, or decreased flexibility of the affected joint. The texture of the skin may become hyperkeratotic, with verrucous and vesicular skin lesions. With upper-extremity involvement, the patient may have difficulty fitting the affected area into clothing or wearing previously well-fitting rings, watches, or bracelets. Similar difficulties with lower-extremity lymphedema include a sensation of tightness or difficulty wearing shoes, itching of the legs or toes, burning sensation in the legs, or sleep disturbance and loss of hair. Ambulation can be affected because of the increased size and weight of the affected limb. Activities of daily living, hobbies, and the ability to perform previous work tasks may also be affected.