Swollen legs

Leg swelling must never be assumed to be due to peripheral oedema. A definite diagnosis of the underlying cause of leg swelling must be made and a careful history and examination, along with appropriate confirmatory tests, are essential. Swelling of the legs may be either unilateral or bilateral:

• Bilateral swelling is usually due to systemic conditions (eg, cardiac failure) and unilateral is often due to local trauma, venous disease or lymphatic disease.

• Unilateral leg swelling is more often due to local causes (eg, deep vein thrombosis or cellulitis). However, bilateral swelling from systemic causes may be much more obvious on one side than the other and therefore can appear to be unilateral swelling.

See the related separate Peripheral oedema article for more details about causes, assessment and management of oedema.

Causes of swollen legs (aetiology)^{1 2}

The most common cause of swelling of the legs is peripheral oedema, which is excessive accumulation of fluid in the interstitial space; however, any tissue of the legs can be swollen. There are therefore a large number of potential causes of swollen legs.

Localised causes of swollen legs

• Trauma (fracture, haematoma, muscle injury).

• Deep vein thrombosis.

• Chronic venous insufficiency and lipodermatosclerosis.

• Other venous causes: varicose veins, obstruction of venous return (eg, pregnancy), pelvic tumours, inferior vena cava obstruction, thrombophlebitis.

• Cellulitis.

• Allergic reaction.

• Baker's cyst.

• Rheumatoid arthritis or other inflammatory arthritis.

• Osteomyelitis.

• Lymphoedema: lymphatic obstruction, either congenital (primary) or secondary due to conditions such as malignancy, post-irradiation, surgery, recurrent infection, lymphatic hypoplasia, filariasis.^{3 4}

• Lipoedema: an abnormal build-up of fat deposits, most often affecting hips, buttocks, thighs and knees, and sometimes arms.⁵

• Congenital malformations (eg, arteriovenous fistula).

• Malignancy (eg, of bone or muscle).

• Stasis: paralysis, poor mobility and dependency, obesity.

Systemic causes of swollen legs

• Congestive cardiac failure.

• Hypoproteinaemia - eg, liver failure, nephrotic syndrome, malnutrition, protein-losing enteropathy.

• Acute kidney injury och chronic kidney disease.

• Fluid overload.

• Anaemia.

• Medication - eg, calcium antagonists, non-steroidal anti-inflammatory drugs.

• Hypothyroidism.

• Hereditary angioneurotic oedema.

• Obstructive sleep apnoea.

The nature of the presentation will give essential clues in establishing the diagnosis. Establish if the swelling is:

• Acute or chronic.

• Unilateral or bilateral.

• Acute or chronic (speed of onset).

• Painful or not painful.

A careful history and examination will establish if there are associated symptoms or signs - for example:

• Orthopnoea, paroxysmal nocturnal dyspnoea: heart failure.

• Diarrhoea or other bowel dysfunction: protein-losing enteropathy.

• Painful swollen calf: deep vein thrombosis or inflammation - eg, cellulitis, osteomyelitis.

• Pigmentation: venous insufficiency.

• Immobility.

• Pelvic mass or pregnancy.

The diagnosis may often be clear without the need for further tests. The choice of initial tests will depend on the differential diagnosis based on clinical assessment. Potential initial investigations include:

• Urinalysis: proteinuria suggests renal cause.

• FBC: high white cell count in infection; anaemia.

• Biochemistry: renal function and electrolytes (raised creatinine in renal disease); LFTs (impaired liver function and associated low albumin); glucose (infection associated with diabetes); TFTs (hypothyroidism).

• Clotting screen: abnormal clotting associated with spontaneous haematoma.

• CXR: pulmonary oedema.

• D-dimer blood test: D-dimers are products of fibrin degradation and are raised in patients with venous thromboembolism. Sensitivity of the test is high but specificity is poor.

• ECG: heart failure.

• Ultrasound, CT scan: haematoma, tumour, abdominal or pelvic mass.

• Duplex Doppler, venography: deep vein thrombosis, arteriovenous fistula.

Further investigations may include:

• Echocardiogram: heart failure.

• Lymphangiography: demonstrates cause of lymphoedema and whether due to hypoplasia or obstruction.

• Lymph node biopsy: infection, tumour.

• Renal biopsy.

Management is directed at identification and treatment of the underlying cause.