Deep Vein Thrombosis

Detailed Overview

DVT pathophysiology is classically described by Virchows triad: venous stasis, endothelial injury, and hypercoagulability. The condition often begins in the calf veins and propagates proximally. Prompt diagnosis is critical to prevent acute pulmonary embolism (PE) and long-term post-thrombotic syndrome (PTS), which causes chronic leg swelling, pain, and ulceration.

Epidemiology & Demographics

Annual incidence is approximately 1 per 1,000 adults. Incidence increases exponentially with age, reaching 1 in 100 for those over 80 years. Slight male predominance in older ages. Post-thrombotic syndrome affects up to 50% of patients within 2 years of proximal DVT.

Etiological Mechanism

Provoked DVT arises from transient risk factors like major surgery, trauma, or immobilization. Unprovoked DVT has no identifiable transient risk factor and is often linked to underlying occult malignancy or inherited thrombophilia (e.g., Factor V Leiden).

Primary Causes

Prolonged bed rest, orthopedic surgery (hip/knee arthroplasty), cancer (e.g., pancreatic, lung), oral contraceptives, Factor V Leiden mutation, Prothrombin G20210A mutation, antiphospholipid syndrome.

• Recent major surgery or trauma: Particularly orthopedic surgery or major abdominal/pelvic cancer surgery within the last 4 weeks.
• Immobilization: Hospitalization, bed rest > 3 days, or long-haul flights (>4 hours).
• Active cancer: Ongoing treatment or palliation within the past 6 months.

Thrombogenesis is triggered by endothelial activation (due to hypoxemia from stasis or direct injury), leading to surface expression of tissue factor. This initiates the coagulation cascade. Fibrin network traps red blood cells and platelets, forming a red thrombus. As the thrombus grows, it obstructs venous return, increasing venous pressure, which causes fluid transudation and clinically apparent edema. Thrombus propagation into larger proximal veins increases the risk of macro-embolization to the pulmonary arteries.

Characteristic Clinical Presentation

• Unilateral leg swelling: Asymmetrical swelling, often involving the calf and extending to the thigh depending on the clot level.
• Leg pain or cramping: Often starting in the calf, described as a charley horse or aching heaviness.
• Erythema: Redness or discoloration of the affected skin.

Physical Examination Signs

• Unilateral calf swelling >3 cm compared to the asymptomatic leg (measured 10 cm below tibial tuberosity).
• Pitting edema confined to the symptomatic leg.
• Dilated non-varicose superficial collateral veins.
• Homans sign (pain in calf on forced dorsiflexion of the foot - low sensitivity/specificity).

• Pulmonary Embolism (PE): Embolization of the clot to the pulmonary arterial circulation, presenting with dyspnea, pleuritic chest pain, and hypoxia.
• Post-Thrombotic Syndrome (PTS): Chronic venous hypertension leading to intractable leg edema, pain, hyperpigmentation, and venous stasis ulcers.

Diagnostic Criteria & Guidelines

Diagnosis is based on a structured clinical probability assessment (e.g., Wells Score). If low probability, D-dimer < 500 ng/mL rules out DVT. If high probability or positive D-dimer, diagnosis is confirmed via venous compression ultrasonography showing non-compressibility of a deep vein.

Differential Diagnosis

• Ruptured Bakers cyst
• Cellulitis
• Muscle strain or tear (e.g., gastrocnemius tear)
• Chronic venous insufficiency

Laboratory Tests & Biomarkers

• High-sensitivity D-dimer: Elevated (> 500 ng/mL or age-adjusted upper limit of normal). Negative test rules out DVT in low clinical probability patients.

Imaging Modalities & Findings

• Compression Duplex Ultrasonography (CUS): Lack of full compressibility of the vein lumen under gentle probe pressure. Loss of spontaneous or phasic flow on Doppler.

• Distal DVT
  Thrombosis confined to the calf veins (peroneal, posterior/anterior tibial); lower risk of PE.
• Proximal DVT
  Involves popliteal, femoral, or iliac veins; high risk of PE.
• Phlegmasia Cerulea Dolens
  Massive iliofemoral thrombosis causing near-total venous occlusion, leading to cyanosis, severe pain, and potential arterial ischemia.

Second-Line & Adjunctive Therapy

Vitamin K antagonist (Warfarin) bridged with LMWH or Unfractionated Heparin until INR is therapeutic (2.0-3.0) for two consecutive days. Used if DOACs are contraindicated (e.g., severe renal impairment CrCl < 15 mL/min or antiphospholipid syndrome).

Surgical & Procedural Management

Catheter-directed thrombolysis (e.g., with tPA) or mechanical thrombectomy is reserved for severe iliofemoral DVT or phlegmasia cerulea dolens to prevent limb loss. Inferior Vena Cava (IVC) filter placement if anticoagulation is absolutely contraindicated.

Recommended Lifestyle Changes

• Early ambulation as soon as therapeutic anticoagulation is reached.
• Graduated compression stockings (30-40 mmHg) to relieve acute symptoms and possibly reduce severity of PTS.

Patient Counseling & Advice

Educate on signs of bleeding and when to seek emergency care. Advise against contact sports while on anticoagulants. Discuss the importance of strict adherence to medication to prevent recurrence or PE.

Follow-Up & Monitoring Schedule

Re-evaluate at 3 months to decide on stopping or extending anticoagulation based on bleeding risk vs. recurrence risk. Regular monitoring of renal function if on DOACs, or INR monitoring (target 2.0-3.0) if on warfarin.

Preventive Strategies

In-hospital thromboprophylaxis with Enoxaparin 40 mg SQ daily or unfractionated heparin 5000 units SQ Q8H for high-risk medical/surgical patients. Intermittent pneumatic compression devices if bleeding risk is high.

With prompt anticoagulation, the acute mortality is very low (<1%). Without treatment, risk of symptomatic PE is up to 50%. Recurrence risk is ~30% over 10 years for unprovoked DVT.