Swelling in one leg only: when it may be thrombosis and what to do

One leg more swollen than the other, a calf pain that won't go away, skin that is warmer or reddened. Often it is something harmless, such as a minor muscle injury. But this set of signs can also indicate a deep vein thrombosis: a clot in a deep vein of the leg, which can travel to the lungs.

This article is not meant to frighten, but to help you recognise when it is necessary to act quickly. In a massage clinic, it is also one of the reasons we ask questions before every session.

What deep vein thrombosis is

Deep vein thrombosis is the formation of a clot (thrombus) in a deep vein, almost always in the leg or thigh, sometimes in the pelvis or arm. The clot hinders the return of blood, and the leg swells.

The great risk is that part of the clot comes loose and travels through the circulation to the lungs, causing a pulmonary embolism. Together, deep vein thrombosis and pulmonary embolism make up what is called venous thromboembolism, one of the most frequent causes of cardiovascular disease, after heart attack and stroke (Konstantinides and colleagues, 2020).

Signs of deep vein thrombosis

The signs usually appear in one leg only:

• Swelling of the leg, ankle or thigh, sometimes on one side only and evident when the two are compared.
• Pain or tenderness in the calf or thigh, often described as a cramp or a “muscle ache” that does not go away, and which may get worse on walking or flexing the foot.
• Heat in the area.
• Redness or purplish discolouration of the skin.
• More visible superficial veins.
• A feeling of heaviness or tension in the leg.

Not all the signs appear at the same time, and some thromboses have very mild symptoms. So anyone with risk factors should take even subtle signs seriously.

Signs of pulmonary embolism: call 112

• Sudden shortness of breath, unexplained.
• Chest pain, especially when breathing deeply or coughing.
• Racing heart.
• Coughing up blood.
• Dizziness, fainting, intense anxiety or a feeling of “impending doom”.

Pulmonary embolism can appear even without previous signs in the leg. It is a medical emergency.

Who is at higher risk

Thrombosis generally results from a combination of factors: slower blood flow, damage to the vein wall and a greater tendency of the blood to clot. The main risk factors are:

• Recent surgery, especially orthopaedic (hip, knee), abdominal or oncological.
• Hospital stay or illness that requires spending a long time in bed.
• Immobilisation of the leg, for example with a cast or orthopaedic boot.
• Long journeys (more than 4 hours) by plane, car or coach. The absolute risk is low in healthy people, but increases with the length of the journey and with other risk factors (Kuipers and colleagues, 2007).
• Pregnancy and the first weeks after the birth.
• Combined hormonal contraceptives and hormone replacement therapy.
• Cancer and some cancer treatments.
• Previous thrombosis or a family history of thrombosis.
• Hereditary clotting disorders (thrombophilias).
• Older age, obesity, smoking.
• Some inflammatory, heart and kidney diseases.
• Severe infections, including COVID-19.

Anyone with one or more of these factors who notices signs in the leg should seek assessment quickly, even if the symptoms seem mild.

Other causes of swelling in one leg

Not every leg that is swollen on one side is a thrombosis. Other frequent causes:

• Infectious cellulitis or erysipelas: a skin infection, with sharply demarcated redness, warmth, pain and sometimes fever. It also requires prompt medical treatment.
• Rupture of a Baker's cyst: a cyst behind the knee that ruptures and causes pain and swelling in the calf, very similar to thrombosis.
• Muscle injury (for example, a partial tear of the calf), often after exertion, with sudden pain and sometimes a bruise.
• Superficial thrombophlebitis: a clot in a vein at the surface, with a red, hard, painful cord. It may be associated with deep thrombosis and should be assessed.
• Venous insufficiency that is more marked on one side. See Heavy, tired legs: causes, what helps and when to see a doctor.
• Lymphoedema, for example after surgery or radiotherapy of the groin or pelvis. See Lymphatic drainage: what it is for, indications and when not to have it.
• Sprain or trauma of the ankle or knee.
• More rarely, compression of veins by masses in the pelvis.

Because the signs overlap a great deal, it is not safe to try to tell them apart on your own. The rule of thumb is: a leg swollen on one side only, without an obvious, banal explanation, should be seen by a doctor.

What to do

• Do not massage the leg, do not apply heat and do not have drainage.
• Seek medical assessment the same day: an emergency department, a health centre with same-day care or contact SNS 24 (808 24 24 24), which will direct you to the appropriate place.
• Call 112 if you have shortness of breath, chest pain, coughing up blood, severe dizziness or fainting.
• Bring with you the list of medicines you take and information about recent surgery, hospital stays or travel.

How the diagnosis is made

The doctor assesses the probability of thrombosis based on symptoms and risk factors, often with a clinical scale (such as the Wells score). Depending on the result, they request:

• D-dimers: a blood test which, if normal in a person with a low probability, helps to rule out thrombosis (Wells and colleagues, 2003).
• Venous Doppler ultrasound: an ultrasound scan of the leg veins, the reference test to confirm or rule out thrombosis.

Treatment

Deep vein thrombosis is treated with anticoagulants, medicines that stop the clot growing and reduce the risk of embolism while the body gradually dissolves the thrombus. Treatment generally lasts at least three months, and the doctor sets the duration depending on the cause (NICE, 2020). In many cases, it can be done at home.

Some people develop, in the following months or years, a post-thrombotic syndrome: pain, heaviness, swelling and skin changes in the affected leg (Kahn, 2016). Movement and, when indicated, compression help to control it.

Massage and thrombosis: why not

Massage and lymphatic drainage are contraindicated in a leg with suspected or confirmed untreated thrombosis. The concern is that manipulation could help to dislodge part of the clot. There are case reports of pulmonary embolism associated with massage of legs with undiagnosed thrombosis. They are rare, but serious, and preventable.

That is why a responsible therapist:

• Asks about surgery, travel, immobilisation, pregnancy, hormonal and anticoagulant medication.
• Observes the legs before starting.
• Interrupts or does not begin the session when there are suspicious signs and recommends medical assessment.

After a thrombosis, massage may become possible again, but only with the doctor's authorisation, once anticoagulant treatment is established, and with gentle techniques. Anticoagulants increase the risk of bruising, so the pressure should always be light.

Prevention

• Moving: getting up and walking regularly, especially after surgery (as medically advised).
• On long journeys: get up and walk whenever possible, move your feet and ankles while seated, drink water, avoid excess alcohol and tight clothing. Those with risk factors should ask their doctor about compression stockings or other prevention.
• After surgery or a hospital stay: follow the prescribed prevention (medication, stockings, early mobilisation).
• Hormonal contraceptives: inform the doctor about a personal or family history of thrombosis.
• Maintaining a healthy weight and not smoking.

Summary: what to do in each situation

At Luxmed Clinic

At Luxmed Clinic, in Algés, safety comes before massage. Before each session, the massage therapist asks about your state of health, surgery, travel and medication, and observes the legs. If there are signs that could indicate thrombosis, we do not carry out the session and recommend immediate medical assessment. After a treated thrombosis, we can resume with gentle techniques and with your doctor's authorisation.

If you are unsure whether you can have a massage or drainage, talk to us before booking.

This article is informative and does not replace medical assessment. If thrombosis is suspected, seek medical help immediately.

Frequently asked questions