Thrombophlebitis: a hard, painful lump in a vein

What it feels like

It usually arrives over a day or two. A vein that was soft becomes a firm cord you can feel through the skin. It is tender to touch, sometimes sharply so. The skin over it turns red or darker, and the area feels warm. Sitting with the leg down often makes it ache more.

People very reasonably assume this is a blood clot, and they are right — it is. The question is which kind, finding this out helps unlock the treatment.

How superficial and deep clots differ

The leg has two vein systems. The deep veins run inside the muscle and carry most of the blood back to the heart. The superficial veins sit just under the skin and carry much less.

A clot in a superficial vein — superficial thrombophlebitis — is painful and visible, but it is not the same condition as a deep vein thrombosis. A DVT sits in the deep system, often causes swelling of the whole leg rather than a localised lump, and carries a risk that a fragment travels to the lungs.

So the good news is genuine: a tender cord you can see and feel is usually the less serious of the two. It is still worth having looked at, for two reasons.

Why it is still worth checking

First, the two can coexist. A proportion of people with superficial thrombophlebitis turn out to have a deep clot as well, and you cannot tell by looking or feeling. Only an ultrasound scan can separate them.

Second, the location matters. Superficial veins join the deep system at the groin and behind the knee. A clot that reaches close to one of those junctions is treated differently from one well away from it, because of the risk of it extending into the deep veins. Again, a scan is what tells you.

Why it often means varicose veins

Superficial thrombophlebitis frequently happens in a vein that was already varicose. Blood moves slowly in a vein whose valves have failed, and slow-moving blood clots more readily.

For many people this is how they find out. The lump is what sends them to a doctor, and the scan done to assess it shows the underlying venous incompetence that had been causing the aching and heaviness all along.

NICE guidance recognises this directly: a hard, painful vein with suspected venous incompetence is listed as a reason to refer someone to a vascular service.

What usually happens next

A duplex ultrasound maps the clot and checks the deep veins. Simple measures — keeping moving rather than resting, anti-inflammatory treatment, and sometimes compression — settle most episodes, and the hard cord softens over several weeks. A residual firmness and a brownish mark can persist for a while after the pain has gone, which is normal.

If the scan shows underlying varicose veins, treating them is a separate conversation, and usually one for after the inflammation has settled.

When to seek urgent assessment

Seek urgent assessment if the whole leg swells rather than one area, if the calf becomes generally painful and tight, or if the redness spreads quickly and you feel unwell.

Call 999 for sudden breathlessness, chest pain or coughing blood. These are signs of a clot having travelled to the lungs, and they are an emergency regardless of how the leg looks.