Deep Vein Thrombosis

Deep Vein Thrombosis (DVT) primarily affects the deep veins of the calf, thigh (femoral/popliteal), or pelvis. It is a major cause of morbidity and mortality, primarily through its progression to Pulmonary Embolism (PE). Risk factors are categorized by Virchow's Triad. Clinical diagnosis is unreliable, so the two-level DVT Wells score is used to stratify risk. Patients with a 'likely' Wells score (≥2) should be fast-tracked for a proximal leg vein ultrasound. Those with an 'unlikely' score (<2) should have a D-dimer test to rule out DVT. Management has shifted towards Direct Oral Anticoagulants (DOACs) like Apixaban or Rivaroxaban as first-line therapy. Complications include the post-thrombotic syndrome (PTS), characterized by chronic pain, swelling, and ulceration due to venous hypertension. In some cases, provoked DVT requires a shorter course of anticoagulation (3 months), whereas unprovoked DVT may require long-term therapy after considering the risk of recurrence versus bleeding.

Thrombus formation in the veins occurs via Virchow’s Triad: 1. Stasis (immobility, obesity, pregnancy, varicose veins). 2. Hypercoagulability (malignancy, thrombophilia like Factor V Leiden, dehydration, inflammatory states). 3. Endothelial injury (trauma, surgery, IV catheters). Unlike arterial thrombi (platelet-rich 'white' clots), venous thrombi are 'red' clots composed primarily of a fibrin-rich matrix and trapped red blood cells. DVT usually starts in the calf vein valves where blood flow is sluggish. If the clot propagates proximally to the popliteal, femoral, or iliac veins, the risk of embolization to the pulmonary arteries significantly increases. Over time, the clot may be resolved by fibrinolysis or become organized and incorporated into the vessel wall, potentially damaging the venous valves and leading to chronic venous insufficiency.

Classic presentation: Unilateral calf or thigh pain, swelling, erythema, and warmth. There may be dilated superficial veins or tenderness along the deep vein. Pitting oedema may be present. A difference in calf circumference (>3cm measured 10cm below the tibial tuberosity) is a significant finding. However, DVT can be completely asymptomatic. It is crucial to screen for symptoms of Pulmonary Embolism (shortness of breath, pleuritic chest pain). 'Phlegmasia cerulea dolens' is a rare, life-threatening emergency where massive iliofemoral DVT causes total venous occlusion, leading to limb ischaemia and cyanosis. Identifying 'provoked' vs 'unprovoked' is essential: provoked DVT has an identifiable transient risk factor (e.g., surgery under GA >30 mins, leg fracture), whereas unprovoked DVT suggests an underlying occult malignancy or thrombophilia.

1. Risk Assessment: 2-level Wells Score.
2. Bloods: D-dimer (only if Wells unlikely). FBC, U&Es, LFTs, Coagulation screen (pre-anticoagulation baseline). HbA1c/Calcium (if screening for malignancy in unprovoked).
3. Imaging: Proximal Leg Vein Ultrasound (Doppler) - if positive, DVT confirmed. If Wells is likely but ultrasound is negative, repeat ultrasound in 6-8 days.
4. Malignancy Screen: For all unprovoked cases, perform a thorough history/exam, CXR, and offer age-appropriate screening (e.g., mammogram, PSA), but avoid CT TAP unless symptomatic.

1. Initial Anticoagulation: Offer Apixaban or Rivaroxaban for at least 3 months. If these are unsuitable, LMWH followed by Dabigatran/Edoxaban or Warfarin.
2. Duration:
- Provoked (transient risk): 3 months.
- Unprovoked (or persistent risk): Assess risk/benefit; often long-term (lifelong) anticoagulation is advised.
- Cancer-associated DVT: Offer DOAC (unless GI/urothelial cancer where LMWH may be preferred).
3. Conservative: Early ambulation. Graduated compression stockings are NOT routinely recommended by NICE for DVT treatment/PE prevention, only for managing post-thrombotic syndrome symptoms.
4. Pregnancy: Use LMWH (e.g. Enoxaparin) as DOACs/Warfarin are contraindicated.