It is a primary or secondary disorder of lymphatic drainage. It is a lymphatic disorder that causes severe localized interstitial fluid retention with enlargement of the anatomical region affected. The condition can be inherited or as a result of a birth defect, surgical damage to the lymphatic system, cancer treatments, and parasitic infections. Though incurable and progressive, a number of treatments can ameliorate symptoms. Tissues with lymphedema are at high risk of infection.
Hereditary Lymphedema; Lymphoedema; Lymphatic Edema; Lymphostatic Elephantiasis Syndrome.
There are different types that have been described. They consist of:
Hereditary Lymphedema Type I (Nonne-Milroy Syndrome; Milroy Syndrome; Congenital Hereditary Lymphedema Type): Presents at birth with areas of swelling. The importance of the swelling tends to increase with age, especially during infancy.
Hereditary Lymphedema Type II (Meige Lymphedema; Familial Lymphedema Praecox; Hereditary Lymphedema Tarda): Usually develops during childhood, adolescence, or early adulthood. It produces severe swelling in areas below the waist. It usually includes red skin over areas of swelling and associated discomfort and/or inflammation.
Secondary Lymphedema: Results from inadequate lymphatic drainage as a result of various causes, such as surgery, recurrent lymphangitis, cellulitis, neoplastic invasion of lymphatics, fibrosis following radiotherapy, or scar formation.
Incidence for hereditary lymphedema is estimated at 1:10,000 individuals. However, the incidence for secondary lymphedema is significantly higher. Meige lymphedema represents 80% of all hereditary lymphedema.
Hereditary lymphedemas that are not associated with other malformations usually affect the lower limbs and are inherited as an autosomal dominant trait with variable penetrance (autosomal or sex-linked recessive forms are less common). These nonsyndromic hereditary lymphedemas are categorized by their age of onset, being either congenital (Milroy disease) or having an onset in childhood or around puberty (Meige disease). Lymphedema is associated with various other anomalies, many of which are genetic (autosomal recessive, autosomal dominant, or X-linked recessive inheritance as seen with Turner and Noonan Syndromes.
Several genes may be involved in the development of hereditary lymphedema, including the following:
Vascular endothelial growth factor receptor 3 (VEGFR3), formerly known as FLT4, is located on chromosome 5.
FOXC2, that is responsible for causing the Lymphedema-Distichiasis Syndrome (16q24.3).
At least one (more likely, several) other gene can be responsible for other forms of hereditary lymphedema.
In the primary forms, aplasia or hypoplasia of the lymphatic vessels results in dilatation of extralymphatic spaces. In both primary and secondary forms, lymphatic obstruction from any cause results in increased protein content of the extravascular tissue and, because of its osmotic effect, retention of additional water. This excess extravascular protein often leads to proliferation of fibroblasts and organization of the edema fluid, giving rise to a characteristic firm, nonpitting swelling.