What is post-thrombotic syndrome? 

Post-Thrombotic Syndrome (PTS) is a chronic, long-term complication that develops in the leg following a Deep Vein Thrombosis (DVT). It is characterized by persistent swelling, pain, and skin changes that occur because the original blood clot damaged the delicate one-way valves or caused scarring in the vein walls. In the UK, PTS is recognized as a significant cause of morbidity, affecting a large percentage of DVT survivors. While the initial clot is treated with anticoagulants, the structural damage it leaves behind can lead to permanent venous hypertension (high pressure in the veins). 

What We will cover in this Article 

• The mechanical failure of venous valves after a clot 

• Prevalence data: Who is most likely to develop PTS? 

• Common symptoms and the Villalta grading scale 

• How PTS impacts long-term skin integrity and ulcer risk 

• Daily triggers that exacerbate post-thrombotic symptoms 

• Differentiating between PTS and a new blood clot 

• Clinical management and the role of graduated compression 

PTS Prevalence and Risk Factor Data 

The following table highlights the statistical likelihood of developing PTS based on the location of the original clot and patient adherence to treatment. 

Clot Location	2-Year PTS Risk	Risk of Severe PTS	Primary Impact
Calf Veins (Distal)	~20%	Low (~2%)	Intermittent swelling
Thigh Veins (Femoral)	~40%	Moderate (~10%)	Daily heaviness / Pain
Pelvic Veins (Iliac)	~60%+	High (~25%)	Chronic oedema / Ulcer risk
Recurrent DVT	~75%	Very High	Significant mobility loss

The mechanics of post-clot damage 

In a healthy venous system, valves prevent blood from flowing backward toward the feet. When a DVT forms, it can physically ‘plaster’ these valves against the vein wall or cause them to become scarred and stiff as the body tries to dissolve the clot. 

This damage creates ‘venous reflux’, where blood leaks backward and pools in the lower leg. Additionally, if the original clot did not fully dissolve, it can leave a ‘residual obstruction’ that acts like a narrow point in a pipe, further increasing the pressure. This chronic high pressure forces fluid and metabolic waste into the surrounding tissue, leading to the inflammation and swelling that define PTS. 

Identifying the symptoms: The Villalta Scale 

Clinicians assess the severity of PTS using the Villalta Scale, which combines five symptoms and six physical signs. If you have a history of DVT, monitoring these signs is essential for early intervention. 

Common Symptoms (Patient Reported): 

• Heaviness: A feeling that the leg is made of lead, especially by evening. 

• Pain: A dull, bursting, or throbbing ache in the calf. 

• Cramping: Frequent ‘charley horses’ or night cramps. 

• Itching: Persistent irritation or a ‘burning’ sensation. 

• Tingling: ‘Pins and needles’ (paraesthesia) in the affected limb. 

Physical Signs (Clinical Observation): 

• Oedema: Swelling that leaves a ‘pit’ when pressed. 

• Skin Induration: Hardening or ‘woody’ texture of the skin. 

• Hyperpigmentation: Brownish staining around the ankle. 

• Venous Eczema: Red, flaky, or inflamed skin patches. 

• New Varicose Veins: Developing surface veins that were not there before. 

Triggers for PTS progression 

Living with PTS requires an understanding of daily triggers that can cause the condition to worsen or ‘flare up’. Managing these triggers is the only way to prevent the progression from simple swelling to a venous ulcer. 

• Prolonged Immobility: Sitting or standing still for long periods without engaging the calf muscle pump. 

• High Ambient Heat: Saunas, hot baths, or heatwaves that cause veins to dilate. 

• Sub-optimal Compression: Wearing socks that are too loose or failing to replace them every 3 to 6 months. 

• Minor Trauma: Small bumps or scratches to the affected leg can trigger a non-healing sore. 

Differentiation: PTS vs. Recurrent DVT 

For many patients, the greatest fear is that their PTS symptoms represent a new blood clot. Differentiating between the two is critical for peace of mind and safety. 

Feature	Post-Thrombotic Syndrome (PTS)	Recurrent DVT (New Clot)
Onset	Gradual, builds up during the day	Sudden, often overnight or in hours
Response to Rest	Improves significantly with leg elevation	Pain and swelling persist despite rest
Skin Temperature	Usually normal	Often hot or significantly warmer
Pain Quality	Heavy, throbbing, ache	Sharp, intense, or ‘tearing’ sensation

Conclusion 

Post-Thrombotic Syndrome is the ‘long-term shadow’ cast by a DVT. While it cannot always be avoided, its impact can be managed through a combination of early diagnosis, medical-grade compression, and consistent physical activity. By understanding the mechanics of valve damage and identifying the early signs of PTS, survivors of blood clots can protect their mobility and skin health for years to come. 

If you experience severe, sudden, or worsening symptoms, such as a leg that becomes significantly more swollen than usual, sharp chest pain, or a new open sore, call 999 immediately. 

Authority Snapshot 

This article outlines the chronic management of venous thromboembolism complications based on the Villalta scoring system and NHS clinical pathways. It emphasizes the structural impact of DVT on the vascular system. This information is intended to help patients recognize and communicate their symptoms to their clinical team. 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.