Vein Conditions & Symptoms
When Leg Swelling Is — and Is Not — Caused by Veins
Swollen legs are one of the most common reasons patients arrive at my consulting rooms. Many have already been told — by a friend, a pharmacist, sometimes even a doctor — that "it's probably your veins." Sometimes that is exactly right. Quite often, it is not.
The distinction matters more than most people realise. Treating varicose veins will not help swelling caused by a heart problem, a medication or lymphoedema — and missing a blood clot can be dangerous. Getting the diagnosis right is the single most important step, because it determines everything that follows.
In this article I want to walk you through how I actually think about leg swelling in clinic: what makes me suspect the veins, what points me away from them, and how a simple ultrasound scan settles the question.
What venous swelling typically looks like
From the consulting room
A dead giveaway in vein patients is the symptoms they report at the end of the day.
When the veins are the cause, the swelling usually follows a recognisable pattern:
It is worse at the end of the day
Venous swelling builds up while you are on your feet and improves overnight or when you elevate your legs. Patients often tell me their ankles look normal in the morning and swollen by evening.
It is often one-sided or asymmetric
Vein disease does not usually affect both legs equally. If one ankle is consistently more swollen than the other, the veins move up my list of suspects.
It comes with other venous signs
Heaviness, aching, night cramps, restless legs, visible varicose veins, or skin changes around the ankle — a brownish discolouration (haemosiderin staining), itchy eczema-like patches, or firm, tight skin above the ankle. These skin changes are important: they tell me the vein problem has been present for some time and is starting to damage the tissues. Left untreated, this progression can end in a venous leg ulcer.
When it is not the veins
A large share of the patients referred to me with "venous" swelling turn out to have something else. These are the common alternatives, and the clues that point to each:
Lymphoedema
Swelling caused by the lymphatic system rather than the veins. The giveaway is that it involves the foot and toes — venous swelling usually spares the toes — and it does not settle overnight the way venous swelling does. The skin on the toes becomes thickened, so it cannot be pinched into a fold (doctors call this Stemmer's sign).
Heart, kidney and liver causes
When the body retains fluid, both legs swell together, symmetrically, and there are usually other signs — breathlessness, weight gain, swelling elsewhere. This pattern needs a physician, not a vein surgeon.
A recent case
I recently consulted a patient who presented with severe swelling of both his feet and legs, up to the level of his knees. His duplex ultrasound was normal — and I noticed he was short of breath doing simple movements. He had attributed his newly swollen legs to his veins. A pro-BNP blood test showed he was likely in acute cardiac failure. His veins were never the problem, and treating them would have helped nothing.
Medication
This is one of the most overlooked causes I see. Certain blood pressure tablets — amlodipine is the classic example — cause ankle swelling in a significant number of people who take them. Anti-inflammatories, some diabetic medications and hormone treatments can do the same. If the swelling started within weeks of a new prescription, the medicine chart deserves a close look before any vein is treated.
Lipoedema
A condition of abnormal fat distribution, almost always in women, causing symmetrical enlargement of the legs that characteristically spares the feet — the swelling stops abruptly at the ankle. It is frequently misdiagnosed for years as either obesity or vein disease. Lipoedema is tender to pressure and does not respond to elevation. It can coexist with vein problems, which is why proper assessment matters.
Deep vein thrombosis (DVT)
The one that must never be missed. A blood clot in the deep veins causes swelling that is usually sudden, one-sided, and accompanied by pain, tightness or warmth in the calf. This is a medical emergency — more on this below.
How I actually work it out
The assessment starts with the story. When did the swelling begin? Is it one leg or both? Does it settle overnight? What medications are you on? Then the examination: the pattern of swelling, the state of the skin, whether the toes are involved, whether varicose veins are visible.
But the decisive step is the duplex ultrasound scan — a painless scan performed in the consulting room that shows both the structure of the veins and the direction of blood flow within them. It tells me, within minutes, whether the valves in your veins are leaking (venous reflux), whether there is a blockage or clot, and precisely which veins are involved.
Just as importantly, a duplex scan can rule the veins out. If the scan is normal, I can tell you with confidence that your swelling is not venous — and that treating your veins would be a waste of your time and money. Pointing a patient towards the correct specialist is sometimes the most valuable thing a vein surgeon can do.
Red flags: when swelling needs urgent attention
Seek immediate medical care — same day — if you have:
• Sudden swelling of one leg, especially with pain, tightness or warmth in the calf
• Leg swelling together with breathlessness, chest pain or coughing up blood
These can indicate a deep vein thrombosis or a clot that has travelled to the lungs. Do not wait for an appointment; go to your nearest emergency department.
If it is the veins: what happens next
When the duplex scan confirms venous disease, the good news is that modern treatment is highly effective and far less invasive than the vein stripping of the past. Depending on the findings, treatment may involve compression stockings, ultrasound-guided foam sclerotherapy, or endovenous radiofrequency ablation — a walk-in, walk-out procedure performed under local anaesthetic in our office operating rooms, which seals the leaking vein from the inside.
Most vein treatments are covered by medical schemes. If you are unsure whether your swelling might be venous, our free online vein screening is a sensible first step. And if you have had veins treated before and the swelling has returned, see my page on recurrent varicose veins — recurrence has its own set of causes and needs a specialised approach.
Frequently asked questions
Why are my legs only swollen in the evening?
Swelling that builds through the day and settles overnight is the classic pattern of venous swelling. Gravity works against the leg veins while you are upright; when the valves inside those veins leak, fluid gradually accumulates. It is worth having a duplex ultrasound to confirm the cause.
Can both legs be swollen from veins?
Yes, but venous swelling is usually asymmetric — one leg worse than the other. Swelling that affects both legs equally is more often caused by fluid retention from the heart, kidneys, liver or medication, and should be assessed by your doctor.
Does swelling mean I have a blood clot?
Usually not — most leg swelling has a benign cause. But sudden swelling of one leg, particularly with calf pain or warmth, can indicate a deep vein thrombosis and needs same-day medical assessment.
Will compression stockings fix my swelling?
Compression helps control venous and lymphatic swelling, but it manages the symptom rather than curing the cause. If leaking vein valves are the underlying problem, treating those veins addresses the source. And if the cause is not venous at all, compression alone may be the wrong approach entirely.
Can I have more than one cause of swelling?
Yes, and this is common — for example, vein disease together with medication-related swelling, or lipoedema with a venous component. This is exactly why a proper assessment with duplex ultrasound matters: it identifies which part of the problem is venous and treatable.
About the author — Dr Johan Blignaut
Specialist Surgeon · MBChB (UOFS) FCS(SA)
Dr Blignaut is the founder of Vein Centres South Africa, with dedicated vein centres in Fourways, Johannesburg, Umhlanga, Durban and Somerset West. He is a Medtronic-appointed proctor who trains surgeons from South Africa, Africa and the Middle East in endovenous radiofrequency ablation, and has appeared as a guest expert on SAFM Health Matters and SABC Health Talk.