Can DVT cause long-term leg swelling? 

Yes, a Deep Vein Thrombosis (DVT) can cause permanent, long-term leg swelling, a condition known as Post-Thrombotic Syndrome (PTS). Clinical data shows that approximately 20% to 50% of patients who experience a DVT will develop some degree of PTS within two years of the initial clot. This occurs because the clot can physically damage the delicate one-way valves in the deep veins or leave the vein partially blocked (residual obstruction), leading to chronic high pressure in the leg. 

What We will cover in this Article 

• The mechanical causes of Post-Thrombotic Syndrome (PTS) 

• How DVT permanently alters venous pressure (Venous Hypertension) 

• Clinical data on the prevalence and severity of PTS 

• Identifying the stages of chronic post-clot swelling 

• Daily triggers that worsen long-term leg heaviness 

• Differentiating between a new clot and PTS symptoms 

• Treatment and prevention strategies for long-term management 

PTS Prevalence and Severity Data 

The following table demonstrates the statistical likelihood of developing long-term symptoms following an initial DVT event. 

Time Post-DVT	PTS Development Rate	Severity of Swelling	Impact on Mobility
6 Months	~15%	Mild / Intermittent	Low
1 Year	~30%	Moderate / Daily	Moderate
2 Years	~40% – 50%	Persistent	Significant
5 Years	~55%	Chronic / Skin changes	High

Why DVT leads to chronic swelling 

In a healthy leg, the deep veins are the ‘motorway’ for blood returning to the heart. When a DVT occurs, it acts like a massive road blockage. Even after the body or medication dissolves the clot, the vein wall is often scarred, and the internal valves which prevent blood from flowing backward are frequently destroyed. 

This leads to a condition called chronic venous hypertension. Because the blood can no longer be pumped out of the leg efficiently, the pressure builds up, forcing fluid out of the vessels and into the surrounding tissue. This fluid accumulation is what causes the persistent, heavy swelling that characterizes Post-Thrombotic Syndrome. Data suggests that patients with ‘proximal’ DVTs (clots in the thigh or pelvis) are at a much higher risk of severe long-term swelling than those with clots only in the calf. 

Identifying the stages of PTS 

PTS is not just about swelling; it involves a spectrum of symptoms that can progress over time if the underlying pressure is not managed. Clinicians use the ‘Villalta Scale’ to grade the severity of these changes. 

• Stage 1 (Mild): Slight swelling by the end of the day, feeling of heaviness. 

• Stage 2 (Moderate): Persistent swelling that requires elevation to resolve; skin starts to feel tight. 

• Stage 3 (Severe): Permanent swelling, skin darkening (pigmentation), and the development of venous eczema or ulcers. 

Triggers for PTS flare-ups 

For those living with long-term swelling after a DVT, certain daily triggers can cause a ‘flare-up’ of symptoms. Identifying these helps in the conservative management of the condition. 

• Static Standing: Standing still for more than 30 minutes allows blood to pool without the help of the calf muscle pump. 

• Heatwaves: High temperatures cause veins to dilate, allowing even more fluid to leak into the tissues. 

• Salt Intake: High dietary sodium causes the body to retain more fluid, which settles in the high-pressure leg. 

• Inactivity: Failure to move the leg prevents the mechanical drainage required to clear the oedema. 

Differentiation: New DVT vs. PTS Symptoms 

One of the biggest challenges for patients is knowing if their swelling is a sign of a new blood clot or simply their existing PTS. 

Feature	Post-Thrombotic Syndrome (PTS)	New Deep Vein Thrombosis (DVT)
Onset	Gradual, usually worse by evening	Sudden, often occurs over hours
Improvement	Improves with a night’s rest/elevation	Does not improve with elevation
Skin Colour	Chronic brown/red staining	New dusky red or blue-purple tint
Pain	Dull ache or heaviness	Sharp, intense, or ‘cramping’ pain

Conclusion 

A DVT is often the beginning of a long-term vascular challenge. While blood thinners treat the acute clot, the damage left behind can lead to the chronic swelling of Post-Thrombotic Syndrome. By understanding the data on PTS prevalence and recognizing the triggers that worsen swelling, patients can take proactive steps such as wearing medical-grade compression and maintaining activity to protect their leg health and maintain mobility for the long term. 

If you experience severe, sudden, or worsening symptoms, such as a new sharp pain in your calf, sudden shortness of breath, or if your leg becomes significantly more swollen and redder than usual, call 999 immediately. 

Authority Snapshot 

This article outlines the long-term complications of venous thromboembolism based on the clinical standards of the NHS and the British Society of Haematology. It highlights the use of the Villalta Scale for assessing PTS. This information is intended to help patients understand the chronic nature of post-clot recovery and the importance of ongoing vascular care. Dr. Rebecca Fernandez is a UK-trained physician with an MBBS and experience in general surgery, cardiology, internal medicine, gynecology, intensive care, and emergency medicine. She has managed critically ill patients, stabilised acute trauma cases, and provided comprehensive inpatient and outpatient care. In psychiatry, Dr. Fernandez has worked with psychotic, mood, anxiety, and substance use disorders, applying evidence-based approaches such as CBT, ACT, and mindfulness-based therapies. Her skills span patient assessment, treatment planning, and the integration of digital health solutions to support mental well-being.