Answer:
Primary lymphedema occurs without a known precipitating cause. It is subdivided into 3 types: lymphedema congenita is present at birth; lymphedema praecox occurs during adolescence and is the most common primary form (80%); and lymphedema tarda occurs after the age of 35. Secondary lymphedema is more frequent. The most common cause worldwide is filariasis. Other causes include malignancy, trauma, surgery, and radiation. Milroy's disease is a familial form of lymphedema that is inherited as an X-linked dominant trait with an onset in puberty.
Which involve the deep lymphatic system? The superficial or epifascial system drains the skin and subcutaneous layers. The deep or subfascial system collects the lymph from the muscle, fascia, joints, ligaments, bones and periosteum. Lymphedema is confined to the subcutaneous compartment; the deep muscle compartments remain uninvolved. Extravasation of protein-rich fluid occurs when fluid formation exceeds lymphatic transport capacity. The high-protein edema causes shifts in Starling’s equilibrium, resulting in the accumulation of more fluid. In time, low oxygen tension, decreased macrophage function, and the presence of increasing amounts of protein-rich fluid give rise to a chronic inflammatory state and consequent fibrosis. Excess protein serves as a medium for bacteria, and the resultant infection leads to additional lymphatic dysfunction.