Primary lymphoedema affects only one or two people per 100 000 under 20 years of age. Approximately 10 per cent have a positive family history.
Non familial primary lymphoedema
It has been proposed that all cases of primary lymphoedema are due to an inherited abnormality of the lymphatic system, sometimes termed ‘dysplasia in utero’. However, it is more likely that many sporadic cases occur in the presence of a (near) normal lymphatic system and are, in reality, examples of secondary lymphoedema for which the triggering event has gone unrecognised. In animal models, simple excision of lymph nodes and/or trunks leads to acute lymphoedema that resolves within a few weeks, presumably due to collateralisation. The human condition can only be achieved by inducing extensive lymphatic obliteration and fibrosis, for example by injecting silica particles; even then there may be considerable delay between the injury and the onset of oedema. It is likely that most nonfamilial primary lymphoedema is due to chronic injury over many years due to seemingly trivial (but repeated) bacterial and/or fungal infections, insect bites, barefoot walking (silica), deep venous thrombosis or episodes of superficial thrombophlehitis. Primary lymphoedema is much more common in the legs than the arms. This may be due to gravity and a bipedal posture, the fact that the lymphatic system of the leg is less well developed than that of the arm in terms of the volume of tissue drained, or the increased susceptibility of the lower extremity to trauma and/or infection.
Familial primary lymphoedema
In familial cases it is assumed that there must be some, as yet undefined, genetic susceptibility of the lymphatic system to such injury. This may be:
• a structural problem such as aplasia or hypoplasia
• a functional problem such as defective lymphatic contractility;
• an immune deficiency.
However, at the present time, the exact mechanisms causing familial primary lymphoedema remain speculative.
Congenital lymphoedema (onset at or within a year of birth) is more common in males, more likely to be bilateral and to involve the whole leg, and accounts for less than 5 per cent of primary lymphoedema. Milroy’s disease describes familial lymphoedema that is present at birth or is noticed shortly thereafter. Congenital lymphoedema is also associated with other disorders, such as yellow nail and Pierre—Robin syndrome (micrognathia).
Lymphoedema praecox (onset from 1 to 35 years of age) is three times more common in females than males, has a peak incidence shortly after menarche, is three times more likely to be unilateral than bilateral, usually only extends to the
knee and accounts for about 20 per cent of primary lymphoedema. The familial form is referred to as Meige’s disease and represents about one-third of all cases.
Lymphoedema tarda develops, by definition, after the age of 35 years but, in practice, is a disease of middle age. It is often associated with obesity and, histologically, lymph nodes are replaced with fatty and fibrous tissue. The cause is unknown. Lymphoedema developing for the first time in later life should prompt a thorough search for underlying malignancy, particularly of the pelvic organs, prostate and external genitalia; such malignancy may be found in up to 10 per cent of patients. It is worth noting that in such patients lymphoedema often commences proximally in the thigh rather than distally.
Browse has classified primary lymphoedema on the basis of lymphangiographic findings. These findings are related to the clinical presentations described above.
Some patients with lymphatic hyperplasia possess megalymphatics in which lymph or chyle refluxes freely under the effects of gravity against the physiological direction of flow. The megalymphatics usually end in thin-walled vesicles on the skin surface causing excoriation, secondary infection, fluid electrolyte and protein depletion; serous surfaces of peritoneal (chylous ascites) or pleural (hydrothorax, chylothorax) cavities; or mucosal surfaces of the intestine (protein losing enteropathy), kidney or bladder (chyluria).
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