32.2 Deep Vein Thrombosis & Superficial Thrombophlebitis

Deep Vein Thrombosis: Pathophysiology & Clinical Assessment

Deep vein thrombosis (DVT) and pulmonary embolism (PE) collectively constitute venous thromboembolism (VTE), which affects an estimated 1 to 2 per 1,000 individuals annually in the United States. DVT occurs predominantly within the deep venous system of the lower extremities, developing when factors satisfying Virchow's Triad converge: (1) venous stasis (immobilization, prolonged travel, paralysis, heart failure), (2) endothelial vascular injury (surgery, trauma, central venous catheterization), and (3) hypercoagulability (active malignancy, pregnancy, estrogen therapy, inherited thrombophilias such as Factor V Leiden, or antiphospholipid syndrome).

Clinical Presentation & Physical Exam Nuances

• Symptoms: Unilateral leg pain, dull aching or heaviness that worsens with ambulation, dependent swelling, erythema, and localized warmth.
• Calf Circumference Measurement: The circumference of both calves must be measured using a flexible tape measure exactly 10 cm below the tibial tuberosity. A difference greater than 3 cm between the symptomatic and asymptomatic leg is a sensitive and validated predictor of acute DVT.
• Homans Sign Pitfall: Pain in the calf upon abrupt, forced passive dorsiflexion of the foot with the knee flexed (Homans sign) is historically notorious. Clinical studies demonstrate that Homans sign has an unacceptably low sensitivity (~30%) and specificity (~50%), and vigorous manipulation theoretically risks mechanical dislodgement of a fragile, non-adherent thrombus into the pulmonary circulation. It should never be used to confirm or exclude DVT.

---

The Wells Clinical Prediction Rule for DVT

Clinical examination alone is notoriously inaccurate for diagnosing DVT (diagnostic accuracy <50%). The validated Wells Clinical Prediction Rule integrates clinical risk factors to calculate pre-test probability, guiding subsequent diagnostic testing:

Clinical Probability Stratification and Diagnostic Pathways

• Two-Tier Model (Recommended in Outpatient Primary Care):
  • DVT Unlikely: Total Score <2 points (pre-test probability ~5% to 6%).
  • DVT Likely: Total Score ≥2 points (pre-test probability ~25% to 40%).
• Three-Tier Model:
  • Low probability: 0 points (~5% risk).
  • Moderate probability: 1 to 2 points (~17% risk).
  • High probability: ≥3 points (~53% to 75% risk).

                WELLS CLINICAL PREDICTION ALGORITHM FOR DVT

                       Calculate Wells Clinical Score
                                      │
               ┌──────────────────────┴──────────────────────┐
               ▼                                             ▼
       DVT UNLIKELY (<2)                              DVT LIKELY (≥2)
               │                                             │
               ▼                                             ▼
      High-Sensitivity D-Dimer                     Proximal Compression US
      (Apply Age-Adjusted Cutoff)                  (CUS) within 24 hours
         │                 │                                 │
         ▼                 ▼                         ┌───────┴───────┐
      Normal            Elevated                     ▼               ▼
   DVT Excluded!     Proceed to CUS              Positive        Negative
   No ultrasound        Ultrasound                   │               │
                                                     ▼               ▼
                                                Treat DVT      High suspicion?
                                                               Repeat CUS in 5-7d

---

D-Dimer Biomarker Strategy: Standard & Age-Adjusted Thresholds

D-dimer is a degradation product of cross-linked fibrin produced during endogenous plasmin-mediated fibrinolysis. High-sensitivity D-dimer assays (quantitative ELISA or automated turbidimetric tests) exhibit an exceptional sensitivity (>95% to 98%) and negative predictive value (>99%), making a normal result invaluable for safely ruling out VTE.

Limitations and Causes of False Positives

D-dimer has notoriously poor specificity (~40% to 50%). Circulating levels increase physiologically with advancing age and pathologically during conditions characterized by tissue inflammation or fibrin deposition: pregnancy, active malignancy, recent trauma or major surgery, infection/sepsis, liver disease, and systemic rheumatologic disorders. Therefore, D-dimer testing should NEVER be ordered in patients with a high pre-test probability (Wells ≥2), as a negative result does not reliably exclude DVT and imaging is mandatory regardless.

The Age-Adjusted D-Dimer Strategy

In patients older than 50 years, physiologic elevations in baseline D-dimer lead to excessive false-positive results, triggering costly and unnecessary ultrasonography or CT scans. The landmark ADJUST-PE study validated the age-adjusted D-dimer strategy:

• Patients ≤50 years of age: Standard cutoff is 500 µg/L (or 0.5 µg/mL fibrinogen equivalent units [FEU]).
• Patients >50 years of age: Age-adjusted cutoff = Patient's Age × 10 µg/L.
  • Example: In a 74-year-old patient with an "unlikely" Wells score, a D-dimer result of 680 µg/L is considered negative because it is below their age-adjusted threshold (74 × 10 = 740 µg/L). DVT is safely excluded without an ultrasound.
  • This approach increases specificity by 20% to 30% in elderly cohorts without increasing false-negative rates (three-month thromboembolic failure rate remains <0.3%).

---

Compression Venous Ultrasonography (CUS) Protocols

Venous duplex ultrasonography combining B-mode imaging with color and spectral Doppler is the gold-standard modality for diagnosing DVT. The single definitive diagnostic criterion for DVT is the absence of complete luminal compressibility of the venous walls under gentle, direct ultrasound transducer pressure.

Diagnostic Protocols

1. Proximal Compression Ultrasonography (Proximal CUS):
   • Evaluates the common femoral vein at the groin, the bifurcation of the femoral and deep femoral veins, and the popliteal vein down to its trifurcation in the popliteal fossa.
   • Proximal CUS is rapid and highly accurate for proximal DVT (sensitivity ~95%, specificity ~98%).
   • Mandatory Serial Protocol: Up to 20% to 30% of symptomatic DVTs originate in the calf veins. If proximal CUS is negative in a patient categorized as DVT likely (Wells ≥2) or with an elevated D-dimer, the clinician must repeat a proximal CUS in 5 to 7 days. This detects isolated calf-vein thrombi that propagate proximally into the popliteal vein (which occurs in ~20% of untreated calf thrombi within 1 to 2 weeks).
2. Whole-Leg Duplex Ultrasonography:
   • Evaluates both the proximal veins and the deep calf veins (posterior tibial, peroneal, and anterior tibial veins).
   • Advantage: A single negative whole-leg scan rules out both proximal and distal DVT, eliminating the need for a repeat 5- to 7-day ultrasound.
   • Controversy / Management of Isolated Distal (Calf) DVT: Isolated calf DVTs have a very low risk of fatal PE (<1% to 2%). In stable outpatients without severe symptoms or risk factors for propagation, international guidelines (CHEST) permit either: (a) therapeutic anticoagulation for 3 months, OR (b) serial duplex imaging at 1 and 2 weeks to monitor for proximal extension without immediate anticoagulation.

---

Outpatient Direct Oral Anticoagulant (DOAC) Pharmacotherapy

The American College of Chest Physicians (CHEST) and American Society of Hematology (ASH) guidelines unequivocally recommend direct oral anticoagulants (DOACs) over low-molecular-weight heparin (LMWH) and vitamin K antagonists (warfarin) for acute lower extremity DVT in non-pregnant outpatients without severe renal dysfunction or antiphospholipid syndrome.

First-Line DOAC Monotherapy Regimens (No Parenteral Lead-In Required)

• Apixaban (Eliquis) (Direct Factor Xa Inhibitor):
  • Loading Dose: 10 mg PO twice daily for 7 days.
  • Maintenance Dose: 5 mg PO twice daily thereafter.
  • Clinical Advantage: Lowest gastrointestinal bleeding risk among all DOACs; approved for use without parenteral bridging.
• Rivaroxaban (Xarelto) (Direct Factor Xa Inhibitor):
  • Loading Dose: 15 mg PO twice daily WITH FOOD for 21 days.
  • Maintenance Dose: 20 mg PO once daily WITH FOOD thereafter.
  • Clinical Pearl: Doses ≥15 mg must be taken with the largest meal of the day; taking rivaroxaban on an empty stomach reduces bioavailability by 34%, risking therapeutic failure.

Alternative Regimens Requiring Initial Parenteral Anticoagulation

• Dabigatran (Pradaxa) (Direct Thrombin Inhibitor): Dosed at 150 mg PO twice daily, but REQUIRES a minimum of 5 to 10 days of initial parenteral anticoagulation (e.g., enoxaparin 1 mg/kg SC q12h) before starting oral dabigatran.
• Edoxaban (Savaysa) (Direct Factor Xa Inhibitor): Dosed at 60 mg PO once daily (30 mg daily if CrCl 15-50 mL/min or weight ≤60 kg), also REQUIRES ≥5 days of initial parenteral anticoagulation.
• Warfarin (Coumadin) (Vitamin K Antagonist): Target INR 2.0 to 3.0. Requires continuous bridging with LMWH or unfractionated heparin for a minimum of 5 days AND until the INR is ≥2.0 for at least 24 consecutive hours.

                DOAC DOSING COMPARISON FOR ACUTE DVT

     DRUG         INITIAL LOADING PHASE       MAINTENANCE PHASE    HEPARIN BRIDGE?
     ─────────────────────────────────────────────────────────────────────────────
     Apixaban     10 mg PO BID x 7 days       5 mg PO BID               NO
     Rivaroxaban  15 mg PO BID x 21 days      20 mg PO Daily (with food) NO
     Dabigatran   Parenteral LMWH x ≥5-10 d   150 mg PO BID             YES (≥5 days)
     Edoxaban     Parenteral LMWH x ≥5-10 d   60 mg PO Daily            YES (≥5 days)
     Warfarin     Parenteral LMWH x ≥5 d      Target INR 2.0-3.0        YES (Until INR ≥2)

Duration of Anticoagulation

• Provoked DVT by a Transient Major Risk Factor (e.g., major surgery, prolonged bed rest >3 days, major trauma): Treat for exactly 3 months, then discontinue.
• Unprovoked DVT or Persistent Risk Factor (e.g., active cancer, chronic medical immobilization): Treat for a minimum of 3 to 6 months, followed by indefinite extended-phase anticoagulation provided bleeding risk is acceptable.

---

Superficial Venous Thrombosis (SVT / Superficial Thrombophlebitis)

Superficial venous thrombosis (SVT)—frequently referred to as superficial thrombophlebitis—is an inflammatory thrombosis of a superficial vein, most frequently the great saphenous vein (GSV, ~70% to 80%) or small saphenous vein (SSV, ~15%).

Clinical Presentation and Diagnostic Imperative

• Clinical Presentation: Erythematous, indurated, exquisitely tender, warm palpable cord tracking along the anatomic path of a superficial vein. Patients may have surrounding cutaneous edema and warmth, frequently misdiagnosed as bacterial cellulitis.
• Mandatory Duplex Ultrasonography: Clinical diagnosis alone is hazardous. A complete lower extremity venous duplex ultrasound must be performed in every patient with suspected SVT because:
  1. 15% to 25% of patients with clinically isolated SVT have concomitant occult deep vein thrombosis (DVT) at the time of presentation.
  2. The ultrasound determines the exact anatomical thrombus length and its distance from deep venous junctions (saphenofemoral junction [SFJ] in the groin or saphenopopliteal junction [SPJ] in the popliteal fossa).

---

Risk-Stratified Management Hierarchy for SVT (High vs. Intermediate vs. Low Risk)

Evidence-based guidelines (CHEST 2021, European Society for Vascular Surgery [ESVS]) categorize SVT into three distinct tiers based on anatomical extent and proximity to the deep venous circulation:

1. High-Risk SVT (Treated as Deep Vein Thrombosis)

• Criteria: Thrombus length ≥5 cm AND extending to within 3 cm (or 3 to 5 cm) of the Saphenofemoral Junction (SFJ) or Saphenopopliteal Junction (SPJ).
• Pathophysiology: Thrombus approaching within 3 cm of the junction behaves clinically like a deep vein thrombosis, carrying an imminent risk of extending across the junctional valve into the common femoral or popliteal vein and embolizing to the lungs.
• Management: Full-dose therapeutic anticoagulation for 3 months (e.g., apixaban 10 mg BID x 7 days then 5 mg BID; or rivaroxaban 15 mg BID x 21 days then 20 mg daily; or therapeutic LMWH), managed identically to acute proximal DVT.

2. Intermediate-Risk SVT (Prophylactic Anticoagulation)

• Criteria: Thrombus length ≥5 cm AND located greater than 3 cm away from the SFJ and SPJ, with or without underlying risk factors (prior VTE, malignancy, oral contraceptives).
• Evidence Base:
  • The CALISTO Trial (NEJM): 3,002 patients with acute SVT ≥5 cm and >3 cm from junctions randomized to Fondaparinux 2.5 mg SC once daily for 45 days vs. placebo. Fondaparinux produced an 85% relative risk reduction in death, DVT, and PE (0.9% vs. 5.9%, p<0.001) without increasing major bleeding.
  • The SURPRISE Trial: Demonstrated that oral Rivaroxaban 10 mg PO once daily for 45 days was non-inferior to subcutaneous fondaparinux 2.5 mg daily for composite symptomatic DVT, PE, and thrombus extension.
• Management: Prescribe Fondaparinux 2.5 mg SC daily for 45 days OR Rivaroxaban 10 mg PO daily for 45 days.

3. Low-Risk SVT (Conservative / Non-Pharmacologic Management)

• Criteria: Thrombus length <5 cm AND remote (>3 to 5 cm) from the SFJ/SPJ, or confined to isolated tributary/varicose veins.
• Management:
  • Symptom Relief: Warm, moist compresses applied for 20 minutes 3 to 4 times daily.
  • Anti-Inflammatory Analgesia: Oral nonsteroidal anti-inflammatory drugs (NSAIDs; e.g., ibuprofen 600 mg PO TID or naproxen 500 mg PO BID for 7 to 14 days) to reduce localized pain and inflammation.
  • Mechanical Support: Below-knee graduated compression stockings (20 to 30 mmHg).
  • Ambulation: Active walking is strongly encouraged; bed rest is strictly contraindicated to prevent stasis.
  • Follow-up: Repeat duplex ultrasound in 7 to 10 days if symptoms progress, pain worsens, or erythema extends proximally toward the groin.