Leg swelling generally occurs because of an abnormal accumulation of interstitial fluid - oedema - of the lower extremity and it may be bilateral or unilateral. The commoner causes of leg swelling are summarised in Commoner causes of leg swelling. Lesions that result in discrete leg swellings are not discussed in this chapter. Systemic causes include cardiac failure, renal failure and hypoproteinaemia, and patients who present with bilateral leg swelling should have these causes excluded. Localised causes may result in either unilateral or bilaterial swelling depending on the site of the ‘localised problem’. The most common localised cause of a unilateral leg swelling is venous disease. Lymphoedema is almost always secondary to a disorder of lymph nodes since primary lymphoedema is a rarity.
Pathophysiology of leg swelling
There is normally a balance between the inflow and outflow of extracellular fluid as blood flows through capillaries. Pressures influencing net movement of fluid in and out of capillaries (Reproduced with permission from A G Guyton and J E Hall, Textbook of Medical Physiology. 10th ed. Philadelphia: W B Saunders Company; 2000). shows the four basic forces that determine the rate of accumulation of interstitial fluid:
- capillary pressure
- interstitial fluid pressure
- plasma colloid osmotic pressure
- interstitial fluid colloid osmotic pressure
The capillary and interstitial fluid pressure are opposed by an oncotic gradient that is determined by the different protein concentrations of the interstitial and intravascular fluid compartments. About 90% of the fluid that leaks from the capillaries is estimated to return into the post-capillary venules, while the remaining 10% enters the lymphatic system.
Oedema can be caused by:
- increased filtration pressure as a result of
- arteriole dilatation
- venule constriction
- raised venous pressure
- reduced oncotic pressure
- accumulation in interstitial space
- increased capillary permeability
- reduced lymphatic removal of exudate
Systemic causes of leg swelling
Congestive cardiac failure
Congestive cardiac failure (right heart failure) is a common cause of bilateral leg swelling. Venous pressure is increased proximal to the failing right heart, as demonstrated clinically by raised jugular and central venous pressures. Post-capillary venous pressure and intravascular hydrostatic pressure are increased consequently. Also, fluid may be retained because of reduced glomerular filtration and secondary aldosteronism. Excessive fluid intake, which may be iatrogenic, and hypoproteinaemia also contribute to leg swelling.
Renal failure results in the inability to excrete water and expansion of the extracellular fluid compartment, unless fluid restriction is instituted. If renal disease is complicated by the nephrotic syndrome, hypoproteinaemia is an additional factor contributing to leg swelling.
A low concentration of plasma proteins, particularly albumin, is a common cause of leg swelling in hospitalised patients. Hypoproteinaemia reduces plasma osmotic pressure and so alters the balance of opposing forces across the capillary wall in favour of fluid leaking out of capillaries into the interstitial space. Hypoproteinaemia causes a generalised oedema, but is more apparent in regions of increased hydrostatic pressure, especially gravity-dependent limbs. Hypoproteinaemia is due to either increased protein loss (extensive burns, tissue catabolism, proteinuria, protein-losing enteropathy, gastrointestinal fistulas, paracentesis), decreased synthesis by the liver (acute or chronic liver disease, malnutrition, malabsorption), or fluid overload.
Localised causes of leg swelling
Venous hypertension or obstruction increases intravascular hydrostatic pressure and reduces movement of fluid into the venous end of capillaries, with subsequent rapid accumulation of dilute interstitial fluid. Varicose veins secondary to saphenofemoral incompetence alone are associated only rarely with marked oedema. However, failure of the normal calf muscle pump, due to valvular incompetence or deep vein obstruction, results in failure of the normal reduction of hydrostatic pressure within superficial veins, which occurs with exercise. Incompetence of several perforating veins leads to only mild oedema because the calf pump mechanism can still lower superficial venous pressures to some extent. Gross unilateral oedema results from occlusion or stenosis of the femoral or iliac veins. Bilateral swelling results from occlusion or extrinsic pressure on the inferior vena cava or major pelvic veins. Deep vein thrombosis is discussed in Chapter 54.
Lymphatic obstruction reduces the clearance of fluid and protein from the interstitial space, resulting in an increased amount of interstitial fluid with a relatively high protein concentration (lymphoedema). Lymphoedema usually develops slowly. The high protein content of lymphoedema eventually leads to subcutaneous fibrosis. Movement of fluid and protein in and out of capillaries is essentially normal. Lymphatic disorders are discussed in Chapter 54.
As part of the inflammatory response to injury, vasoactive amines and peptides are released from damaged cells and produce vasodilatation and increased capillary permeability. Fluid and plasma proteins, in addition to cells, leak out of capillaries into the interstitial space and cause swelling. Oedema may be limited to the inflamed area but may drain by gravity to the dependent part of the limb, often causing circumferential swelling of the leg and swelling of the dorsum of the foot. Repeated acute infections (cellulitis, lymphangitis) or chronic infections (fungal infections, filariasis, tuberculosis) produce secondary lymphoedema because of lymphatic obstruction. Lymphoedema and chronic leg swelling may be complicated by infection, which increases swelling of the limb.
Assessment of the swollen leg
As with all medical problems, assessment relies on the history, examination and appropriate investigations.
Specific inquiry is made for symptoms suggesting disorders of the heart (chest pain, dyspnoea, paroxysmal nocturnal dyspnoea, palpitations, haemoptysis, hypertension), gastrointestinal tract (abdominal pain and distension, indigestion, vomiting, haematemesis, diarrhoea, rectal bleeding, alcohol intake, drug ingestion, jaundice) and kidneys (back pain, dysuria, haematuria, nocturia, urine volume, frothy urine, tiredness, lethargy). Recent nutritional intake must be considered, especially in hospitalised patients who may become malnourished because of long periods of anorexia, nausea, vomiting, gastrointestinal dysfunction, or fasting for investigations and treatment. Similarly, in hospitalised patients, the volume of intravenous fluid infusions must be reviewed. The duration and rapidity of onset of leg swelling must be ascertained. Family history of similar problems may be relevant. Past history of varicose veins, malignant disease, radiotherapy, surgery, previous episodes of leg swelling or infection, or deep vein thrombosis (perhaps complicating surgery or childbirth) must be identified.
A full physical examination must be performed. General points of examination include the patient's nutritional status, and abnormal pigmentation of the skin, sclera and mucous membranes. Look at the abdomen and lower limbs for the presence of suspicious skin lesions and vascular abnormalities, surgical scars, and signs suggestive of radiotherapy (skin atrophy, telangiectasia, scaly skin).
Swelling of one or both legs is confirmed by inspection and measurement at a designated point. Remember that the swollen limb may be tender to touch. Pitting oedema is determined by slow, gentle pressure over the medial malleolus or the shaft of the tibia. Lymphoedema is characterised by non-pitting swelling of the leg and the foot, as well as swelling of the toes. Intradermal vesicles, weeping of the skin, dry and scaly skin, and an ‘elephant skin’ appearance occur in longstanding cases. The legs are examined for signs of venous disease (varicose veins, venous flares, pigmentation, liposclerosis, eczema, venous ulceration). The Trendelenburg test is performed (Chapter 54). An arteriovenous fistula is characterised by a pulse, thrill and bruit over dilated veins. The hip, knee and ankle joints should be examined, together with the popliteal fossa. Regional lymph node groups must be examined. Rectal and pelvic examinations may be indicated.
Signs of inflammation (erythema, heat, tenderness, swelling, reduced movement) with or without infection (pus) should be noted. Tinea pedis between the toes and on the soles of the feet leads to cracking and breakdown of the skin, and may produce the portal of entry for bacteria causing cellulitis of the legs and feet (see Surgical infections).
A full blood examination; erythrocyte sedimentation rate; levels of serum creatinine, urea and electrolytes; liver function tests and levels of plasma proteins and albumin are measured. An electrocardiograph and chest X-ray are performed. Urinalysis for blood and protein is performed. Abdominal ultrasound scan or computed axial tomography is required to define organomegaly or tumour mass.
If venous disease is suspected, a Doppler study of the deep veins is performed to detect patency. Venography demonstrates the deep veins, the extent of stenosis or obstruction, and the presence of collateral circulation.
Lymphangiography may be attempted when venous and other diseases have been excluded. It may fail to demonstrate any lymphatics, or may show a reduced number of lymphatics, lymphatic dilatation proximal to obstruction, lymphatic valve incompetence, or lymph node disease.
The treatment of leg swelling depends on the cause. Cardiac, hepatic and renal disorders are treated along medical lines. Protein deficiency is treated by nutritional supplementation, either orally, enterally or intravenously (see Nutrition and the surgical patient). Infective conditions are treated with antibiotics with or without surgical drainage. Specific treatments of venous and lymphatic diseases are discussed in Chapter 54. Non-specific measures that help in the treatment of the swollen leg include wearing elastic support stockings, elevation and massage.
The use of elastic stockings is described in Chapter 54.
Simple elevation of the leg relieves oedema by reducing intravascular hydrostatic pressure. The principle is to avoid having the swollen leg in a dependent position and to avoid having it still. First, patients must keep off their feet as much as possible, and elevate the affected limb above the level of the hip whenever sitting. The limb should be raised above the horizontal whenever possible and, ideally, the patient should lie on the floor with the legs vertically against a wall for 15–20 minutes several times each day. This may not be practical for many patients but should be advised and encouraged. Second, when patients are standing, they should avoid standing still and should be encouraged to exercise the calf muscles and to walk with a support stocking. Third, the foot of the bed should be elevated by at least 10 cm.
Massage of the limb towards the hip, using a surface skin oil, reduces subcutaneous tissue swelling and helps keep the skin and subcutaneous tissues soft and supple.