Acute Superficial Thrombophlebitis

Overview

Acute superficial thrombophlebitis, also called superficial vein thrombosis (SVT), is a blood clot in a vein just beneath the skin, accompanied by inflammation of the vein wall. It is common, and it most often affects the legs. Although it was traditionally regarded as a minor, self-limiting problem, ultrasound studies have shown that SVT can extend into the deep venous system and is sometimes accompanied by deep vein thrombosis (DVT) or pulmonary embolism (PE). Careful assessment is therefore important.

Causes and risk factors

• Varicose veins, the most common setting, in which slow, disturbed flow favours clotting
• Previous SVT or venous thromboembolism (VTE)
• Pregnancy and the postpartum period, and oestrogen therapy (oral contraceptive pill, HRT)
• Obesity, older age, prolonged immobility, recent surgery or trauma
• Active cancer, or an inherited or acquired clotting tendency (thrombophilia)
• Intravenous cannulas, infusions or injections (the usual cause in the arm)
• Inflammatory conditions such as Behçet’s disease or Buerger’s disease (rare)

Clinical features

• A tender, warm, red, firm cord along the course of a superficial vein, often with surrounding skin redness
• Pain that is worse on standing or walking, with mild swelling around the vein
• Most often the great saphenous vein and its tributaries in the leg, less often the small saphenous vein
• Low-grade fever in some patients, though fever with spreading redness should raise concern about infection (suppurative thrombophlebitis, mainly cannula-related)
• Recurrent or migratory episodes in different veins, which may signal an underlying systemic cause such as malignancy or a thrombophilia

SVT is a clinical diagnosis but is easily confused with cellulitis, lymphangitis, erythema nodosum, panniculitis or DVT. Calf swelling or a swollen limb suggests a coexisting DVT.

Natural history

In most patients with a short segment of thrombosis, pain and tenderness settle over one to three weeks. The vein then becomes a firm, fibrous cord that may take months to soften, often leaving skin pigmentation. Recurrence is common when the underlying varicose veins are left untreated.

The main concern is clot propagation:

• Thrombus can extend along the vein towards the saphenofemoral junction (SFJ) in the groin or the saphenopopliteal junction (SPJ) behind the knee, and from there into the deep veins.
• In large registry data (the POST study), about one in four patients with lower limb SVT had a coexisting DVT at diagnosis, and around 1 in 20 had symptomatic PE.
• Of patients without DVT at presentation, a minority developed symptomatic VTE or clot extension in the following weeks when not anticoagulated.

The risk is greatest with longer segments of thrombus (5 cm or more), thrombus close to the SFJ or SPJ, involvement of the main saphenous trunks above the knee, and additional risk factors such as prior VTE, cancer or thrombophilia.

Investigations

Duplex ultrasound is the key investigation. It is recommended for lower limb SVT to:

• confirm the diagnosis and exclude cellulitis or other causes
• identify which vein is involved (great saphenous, small saphenous or a tributary) and measure the length of thrombus
• measure the distance of the thrombus from the SFJ or SPJ
• exclude concurrent DVT in both legs
• map the underlying venous reflux and varicose veins for later treatment

Blood tests are not routinely needed. D-dimer is unhelpful because it is elevated by the inflammation itself. Inflammatory markers and cultures are used if infection is suspected. Thrombophilia testing and cancer screening should be reserved for recurrent, migratory, unprovoked or unusual-site SVT, or for patients with a suggestive personal or family history. Cancer screening should follow age-appropriate guidelines, not extensive imaging.

Management

Treatment depends on the ultrasound findings and the patient’s risk profile.

Ultrasound finding	Usual approach
Concurrent DVT	Treat as DVT with full therapeutic anticoagulation
Thrombus within 3 cm of SFJ/SPJ, or extending into the deep system	Therapeutic anticoagulation, generally for at least 3 months, with vascular specialist review
Thrombus 5 cm or longer, more than 3 cm from the junction	Prophylactic-dose anticoagulation for about 45 days (fondaparinux 2.5 mg daily, prophylactic LMWH, or rivaroxaban 10 mg daily)
Short segment (under 5 cm), below the knee, away from junctions	Symptomatic treatment; consider anticoagulation if risk factors are present; repeat ultrasound at about 7 to 10 days to detect extension

The dose, agent and duration should be individualised, and some of these uses are off-label.

Symptomatic measures (all patients)

• Regular walking and avoiding prolonged immobility
• Graduated compression stockings or bandaging, as tolerated
• Warm compresses, and leg elevation at rest
• Topical NSAIDs, or a short course of oral NSAIDs in patients without contraindications, for pain and inflammation

Anticoagulation

The CALISTO trial showed that fondaparinux 2.5 mg daily for 45 days reduced symptomatic VTE, clot extension and recurrence by more than 80% compared with placebo. The SURPRISE trial found oral rivaroxaban 10 mg daily to be a comparable alternative. Guidelines (ESVS 2021, CHEST 2021) support these approaches. Pregnancy calls for LMWH, and DOACs are avoided.

Procedural options

• Office-based evacuation of clot from a thrombosed varicose tributary can give rapid pain relief in selected patients.
• Treating the underlying varicose disease, by endovenous ablation, foam sclerotherapy or phlebectomy, is usually planned once the acute inflammation has settled, to reduce the risk of recurrence.
• Open ligation of the SFJ is now rarely required and is reserved for selected cases.

Special situations

• Cannula-related SVT: remove the cannula; treat with topical therapy and elevation. Suppurative thrombophlebitis needs antibiotics and sometimes surgical excision.
• Recurrent or migratory SVT: investigate for an underlying systemic cause.
• Hormonal therapy: review the need for oestrogen-containing medication.

When to seek urgent medical attention

Key sources

• Kakkos SK et al. ESVS 2021 Clinical Practice Guidelines on the management of venous thrombosis. Eur J Vasc Endovasc Surg 2021
• Stevens SM et al. Antithrombotic therapy for VTE disease: second update of the CHEST guideline. Chest 2021
• Decousus H et al. Fondaparinux for the treatment of superficial-vein thrombosis in the legs (CALISTO). N Engl J Med 2010
• Decousus H et al. Superficial venous thrombosis and venous thromboembolism: a large, prospective epidemiologic study (POST). Ann Intern Med 2010
• Beyer-Westendorf J et al. Rivaroxaban versus fondaparinux for SVT (SURPRISE). Lancet Haematol 2017

This page is general information and does not replace individual medical advice.