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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Virchow triad: stasis + endothelial injury + hypercoagulability
- Diagnosis: Wells score to determine pre-test probability. Low probability + negative D-dimer = DVT ruled out. Moderate-high probability or positive D-dimer = compression ultrasound
- Proximal DVT (popliteal and above): high PE risk, requires anticoagulation. Distal (calf-only): can consider surveillance with serial ultrasound vs anticoagulation
- Treatment: DOAC (apixaban or rivaroxaban — no heparin bridge needed) is first-line. LMWH bridge to warfarin is alternative
- Duration: provoked by transient risk factor (surgery, immobility) = 3 months. Unprovoked or recurrent = consider indefinite anticoagulation with periodic reassessment
Overview
Deep vein thrombosis is formation of a thrombus within the deep venous system, most commonly in the lower extremities. It is part of the venous thromboembolism (VTE) spectrum along with pulmonary embolism. The pathophysiology follows Virchow triad: venous stasis (immobility, paralysis, long flights), endothelial injury (surgery, trauma, central line), and hypercoagulability (inherited thrombophilia, malignancy, pregnancy, OCP/HRT). Proximal DVT (popliteal vein and above) carries significant risk of embolization to the pulmonary vasculature.
Epidemiology
VTE affects ~900,000 Americans annually with ~100,000 deaths. DVT incidence ~1-2 per 1,000/year, increasing sharply with age. Risk factors: recent surgery (especially orthopedic — hip/knee replacement), immobilization, active malignancy (Trousseau syndrome), obesity, OCP/estrogen therapy, pregnancy, prior VTE, inherited thrombophilia (Factor V Leiden most common in Caucasians, prothrombin G20210A), antiphospholipid syndrome, central venous catheters.
Clinical Features
Symptoms
Unilateral leg swelling (asymmetric calf circumference — >3 cm difference is significant)
Calf pain or tenderness, worse with walking
Warmth and erythema of affected leg
May be asymptomatic (up to 50% of DVTs)
Concurrent symptoms of PE: dyspnea, pleuritic chest pain, hemoptysis
Signs
Unilateral pitting edema of affected extremity
Calf tenderness on palpation, especially along deep venous system
Homan sign (calf pain with dorsiflexion) — unreliable, neither sensitive nor specific
Phlegmasia cerulea dolens: massive DVT with venous gangrene — swollen, cyanotic, painful limb — emergency
Palpable cord (thrombosed vein)
Investigations
First-line
Wells score for DVTClinical prediction rule: active cancer (+1), paralysis/immobilization (+1), bedridden >3 days or major surgery <12 weeks (+1), tenderness along deep veins (+1), entire leg swelling (+1), calf swelling >3 cm vs asymptomatic side (+1), pitting edema (+1), collateral superficial veins (+1), previous DVT (+1), alternative diagnosis as likely (-2). Score <=0 = low probability, 1-2 = moderate, >=3 = high
D-dimerHigh sensitivity, low specificity. Useful to RULE OUT DVT only when pre-test probability is low (Wells <=0). Negative D-dimer + low Wells = DVT ruled out. D-dimer is falsely elevated in: age >50, pregnancy, malignancy, infection, post-op, inflammation. Age-adjusted cutoff: age x 10 (ng/mL) if >50 years
Compression ultrasonographyDiagnostic test of choice: non-compressibility of vein with probe pressure = positive for DVT. Sensitivity >95% for proximal DVT, lower for isolated calf DVT. If negative but clinical suspicion remains high: repeat in 5-7 days
Second-line
Whole-leg ultrasoundImages both proximal and distal veins in single study. Reduces need for serial imaging
CT venographyCan be combined with CTPA for concurrent PE evaluation. Alternative if ultrasound technically limited
Specialist
Thrombophilia testingConsider for unprovoked DVT in young patients (<50), recurrent VTE, unusual sites (cerebral, mesenteric, portal), or strong family history. Test AFTER completing anticoagulation (many tests affected by acute thrombosis and anticoagulant drugs). Tests: Factor V Leiden, prothrombin mutation, antithrombin III, protein C/S, antiphospholipid antibodies, lupus anticoagulant
Cancer screeningAge-appropriate screening for unprovoked DVT. Some guidelines suggest CT chest/abdomen/pelvis if no obvious provoking factor in patients >40
1
Anticoagulation — acute treatment
- DOAC is first-line for most patients: apixaban 10 mg BID x 7 days then 5 mg BID, OR rivaroxaban 15 mg BID x 21 days then 20 mg daily. No heparin bridge needed
- Alternative: LMWH (enoxaparin 1 mg/kg SC BID) bridged to warfarin (INR target 2-3). Start warfarin on day 1, continue LMWH until INR >=2 for >=24 h
- Cancer-associated DVT: LMWH or DOAC (edoxaban, rivaroxaban — avoid apixaban/rivaroxaban with GI/GU cancers due to bleeding risk per SELECT-D/Caravaggio). LMWH preferred for GI malignancy
- Renal failure (CrCl <30): UFH or adjusted-dose LMWH; avoid DOACs (limited data, accumulation risk). Warfarin acceptable after bridging
- Pregnancy: LMWH throughout (DOACs and warfarin contraindicated)
2
Duration of anticoagulation
- Provoked by major transient risk factor (surgery, immobility): 3 months
- Provoked by minor transient risk factor (OCP, travel): 3 months (consider stopping the provoking factor)
- Unprovoked (no identifiable trigger): minimum 3 months, then assess for indefinite therapy. If low bleeding risk and patient preference: indefinite. After stopping, can use apixaban 2.5 mg BID or rivaroxaban 10 mg daily for extended prophylaxis (AMPLIFY-EXT, EINSTEIN-CHOICE)
- Cancer-associated: continue as long as active cancer or receiving treatment
- Recurrent unprovoked VTE: indefinite anticoagulation
3
Special situations
- IVC filter: only if anticoagulation absolutely contraindicated (active life-threatening bleeding, recent neurosurgery). Retrievable filter preferred — remove when anticoagulation can be resumed
- Catheter-directed thrombolysis: consider for acute extensive iliofemoral DVT with symptoms <14 days and low bleeding risk, or phlegmasia cerulea dolens
- Compression stockings: no longer routinely recommended to prevent post-thrombotic syndrome (SOX trial showed no benefit). May help with symptomatic relief
Complications
- Pulmonary embolism: ~50% of untreated proximal DVTs embolize. PE is the most feared acute complication
- Post-thrombotic syndrome: Chronic venous insufficiency (pain, swelling, hyperpigmentation, ulceration) — affects 20-50% within 2 years despite anticoagulation
- Phlegmasia cerulea dolens: Massive DVT causing venous gangrene — limb-threatening emergency
- Recurrence: ~10% per year after stopping anticoagulation for unprovoked DVT
- Heparin-induced thrombocytopenia (HIT): If on UFH — paradoxical thrombosis with platelet drop. Switch to argatroban or bivalirudin
USMLE Step 2 CK Exam Tips
- 1Wells score + D-dimer is the algorithm: low Wells + negative D-dimer = ruled out. Otherwise = ultrasound
- 2Apixaban and rivaroxaban can be started without heparin bridging. This is a key advantage over warfarin
- 3Duration: provoked = 3 months. Unprovoked = consider indefinite. Cancer = indefinite while active
- 4Factor V Leiden is the most common inherited thrombophilia in Caucasians (5% heterozygous prevalence)
- 5Homan sign is unreliable — do not use to rule in or rule out DVT
- 6IVC filter: ONLY if anticoagulation absolutely contraindicated. It does not treat DVT, only prevents PE
- 7Unprovoked DVT in patient >40: screen for occult malignancy (age-appropriate cancer screening)
- 8Pregnancy DVT: LMWH only. DOACs and warfarin are contraindicated
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