What is Deep Vein Thrombosis (DVT)?
Deep vein thrombosis (DVT) is the formation of blood clots in the deep veins, most commonly affecting the deep leg veins (calf, popliteal, femoral) or pelvic veins, and represents a potentially life-threatening condition that can lead to pulmonary embolism with mortality rates of 25-30% if untreated. 1, 2
Anatomical Classification
DVT is classified into two major categories based on location, which directly determines risk stratification and treatment urgency:
- Proximal DVT includes thrombosis in the popliteal vein and above (popliteal, femoral, and iliac veins), carrying significantly higher risk of pulmonary embolism (50-60% if untreated) 1, 3
- Distal DVT is defined as thrombosis affecting deep veins of the lower extremity with the most proximal extent being distal to the popliteal vein, including posterior tibial, peroneal, anterior tibial, soleal, and gastrocnemius veins 3, 4
Clinical Presentation
The classic presentation includes:
- Local pain or tenderness in the affected extremity 1
- Edema and swelling of the lower extremity, which may involve the entire leg including the foot and ankle 1, 3
- Approximately one-third of patients with DVT are completely asymptomatic, making clinical diagnosis unreliable without objective imaging 1, 3
- Symptoms often do not appear until there is involvement above the knee 1
Pathophysiology and Risk Factors
DVT develops through three primary mechanisms:
- Hypercoagulability (e.g., procoagulants such as tissue factor expressed by cancer cells) 1
- Vessel wall damage 1
- Vessel stasis from direct compression or prolonged immobilization 1
Additional risk factors include acquired or congenital thrombophilia, surgical procedures, chemotherapeutic regimens, and active malignancy 1
Clinical Significance and Complications
The severity of DVT-related complications varies by location:
- Proximal DVT is associated with pulmonary embolism in 50-60% of untreated cases, with mortality of 25-30% 3, 2
- Proximal DVT has a higher recurrence rate after discontinuation of anticoagulant therapy (approximately 10.3 events per 100 person-years) 3
- Post-thrombotic syndrome develops in approximately 50% of patients with proximal DVT, causing chronic leg pain, intractable edema, and potentially leg ulceration 1, 3
- Distal DVT carries lower embolic risk but has a proximal extension risk of approximately 15-17%, with most extensions occurring within the first 2 weeks 4, 5
Diagnostic Approach
Because clinical assessment alone is unreliable, objective imaging is mandatory when DVT is suspected:
- Duplex ultrasound is the preferred initial imaging modality, with pooled sensitivity of 90.1% and specificity of 98.5% for proximal DVT 1, 6
- Clinical risk stratification using the Wells score combined with D-dimer testing improves diagnostic accuracy 1, 7
- DVT is unlikely if the clinical prediction score is low and D-dimer levels are normal 1
- Whole-leg ultrasound (sensitivity 94.0%, specificity 97.3%) assesses both proximal and distal veins 3, 6
Treatment Implications
Management differs dramatically based on DVT location:
- Immediate anticoagulation is mandatory for all proximal DVTs (including popliteal), with treatment for at least 3 months 3, 5, 2
- For distal DVT, treatment decisions depend on specific risk factors including thrombus length >5 cm, diameter >7 mm, proximity to proximal veins, positive D-dimer, active cancer, or history of prior VTE 4
- Serial imaging surveillance at 1 week is an acceptable alternative to immediate anticoagulation only for selected low-risk patients with isolated distal DVT 3, 4
Critical Pitfalls
- Never assume that absence of symptoms excludes DVT, as one-third of patients are asymptomatic 1, 3
- Anticoagulation should never be withheld for confirmed proximal DVT, as the risk of life-threatening pulmonary embolism far outweighs bleeding risks 3
- Failure to arrange repeat venous evaluation in patients with isolated distal DVT who are not anticoagulated is a critical management error 4