The purpose of this study is to determine whether a limited duration of treatment (two weeks of low molecular weight treatment) is a safe and effective treatment for distal deep vein thrombosis of the lower limb.

Approximately 50% of symptomatic episodes of deep vein thrombosis (DVT) will be confined to the calf veins (distal DVT). The proportion of distal DVT that propagate to the proximal veins, increasing the risk of pulmonary embolism, is not known. The best treatment of isolated distal DVT is therefore controversial and options include no treatment, follow-up scanning and treatment of only those patients with thrombus propagating to proximal veins, and full anticoagulation for periods ranging from 2 weeks to 3 months.

There is good evidence that the 3-month thromboembolic risk in patients with a negative CUS that is limited to the proximal veins is low, in the order of 1%. Previous studies have demonstrated that patients treated with a short period of anticoagulation (4-6 weeks) have a low risk of developing recurrent DVT or PE. In addition, the specificity of CUS for distal DVT is lower than that for proximal DVT, increasing the proportion of false positive findings, making it likely that a proportion of patients diagnosed with distal DVT are treated unnecessarily, with the attendant risks of major and fatal haemorrhage.

The need for anticoagulation of patients with distal DVT to prevent recurrent DVT is therefore uncertain, however a survey of current practice suggested that most patients with this condition currently receive antithrombotic therapy. The impact of anticoagulation on initial patient symptoms, and the subsequent risk of the post-thrombotic syndrome are also unclear, and may be a possible alternative justification for antithrombotic therapy.

In this proposed multicentre, prospective, cohort study, we plan to determine if a shorter duration of anticoagulation (minimum 2 weeks) is a safe and effective treatment for isolated distal vein thrombosis.

Inclusion Criteria:

• Patients aged 18 years or older with acute symptomatic provoked or unprovoked distal vein thrombosis (axial or muscular veins but not involving trifurcation or distal popliteal vein)
• Absence of symptomatic pulmonary embolism

Exclusion Criteria:

• DVT involving trifurcation or more proximal leg veins on imaging
• Prior DVT
• Active malignancy ie present at time of diagnosis, or on treatment, or treatment completed within 3 months
• Ongoing risk factors for propagation e.g. immobility (>50% of day in bed or ≥72 hours), plaster cast or non-weight bearing
• Other indication for therapeutic anticoagulation (e.g. AF)
• Active gastro-oesophageal ulceration or bleeding
• Other high risk for bleeding (e.g. recent neurosurgery, vascular retinopathy, coagulopathy)
• Platelet count <80 x 109/L
• Renal impairment (CrCl <30ml/min) • Pregnancy or lactation