Deep Vein Thrombosis (DVT) - Comprehensive Medical Overview

Definition and Epidemiology

Anatomy of the Lower Limb Venous System

• Distal (calf) veins: Posterior tibial, anterior tibial, peroneal, gastrocnemius, and soleus veins
• Proximal veins: Popliteal, femoral (previously "superficial femoral"), common femoral, and iliac veins

Pathophysiology: Virchow's Triad

1. Endothelial Injury

• Downregulation of coagulation inhibitors (thrombomodulin, endothelial protein C receptor, tissue factor pathway inhibitor)
• Upregulation of tissue factor expression
• Increased secretion of plasminogen activator inhibitors (PAI), which limit fibrinolysis by antagonizing t-PA and urokinase

2. Stasis / Abnormal Blood Flow

• Allowing platelets and leukocytes to contact the endothelium
• Slowing washout of activated clotting factors
• Impeding inflow of clotting factor inhibitors
• Promoting endothelial gene expression changes that favor procoagulant activity

3. Hypercoagulability

• Factor V Leiden mutation - an amino acid substitution renders Factor V resistant to proteolysis by Protein C. Heterozygotes have a 3-4x increased risk; homozygotes have a 25-50x increased risk. Found in ~60% of patients with recurrent DVT. Present in 2-15% of those of European ancestry.
• Prothrombin gene mutation (G20210A) - found in 1-2% of the general population, causes increased prothrombin gene expression
• Protein C or S deficiency - loss of natural anticoagulant control
• Antithrombin III deficiency
• Hyperhomocysteinemia

• Active malignancy (especially pancreatic cancer - "Trousseau's syndrome")
• Prolonged immobility or surgery
• Oral contraceptive pills / hormone replacement therapy
• Pregnancy and puerperium
• Antiphospholipid antibody syndrome
• Heparin-induced thrombocytopenia (HIT)
• Polycythemia vera, thrombocytosis
• Nephrotic syndrome
• Inflammatory bowel disease

Risk Factors

Clinical Features

• Unilateral limb pain and swelling (hallmark signs)
• Mild cramping or a sense of fullness in the calf
• Heaviness or aching of the affected limb
• Most cases are asymptomatic - only ~25% present with symptoms

• Pitting edema of the affected extremity
• Erythema and warmth
• Tenderness to palpation along the deep venous distribution
• Dilation of superficial collateral veins
• Rarely: a palpable venous cord
• Homans' sign (calf pain on dorsiflexion of the foot) - historically used but neither sensitive nor specific

• Left leg predominance: The left iliac vein is vulnerable to compression by the left iliac artery (May-Thurner syndrome), explaining a slightly higher frequency of left-sided DVT
• Bilateral DVT: Found in fewer than 10% of ED patients
• Phlegmasia cerulea dolens: Massive iliofemoral thrombosis causing severe limb swelling, cyanosis, and threatened limb viability
• Upper extremity DVT: >90% occur with an indwelling catheter; in young athletes, the dominant arm can develop effort-induced thrombosis from thoracic outlet compression (Paget-Schroetter syndrome)

Differential Diagnosis

Diagnosis

Step 1: Pre-Test Probability - Wells DVT Score

• Score ≤1: Low probability (~2% pre-test probability)
• Score ≥2: High probability (~28% pre-test probability)

• L = Left leg suspicion (+1)
• E = Edema (+1)
• Ft = First trimester (+1) A LEFt score of 0 or 1 indicates low probability.

Step 2: D-Dimer

• Measures enzymatic breakdown of cross-linked fibrin from any intravascular thrombus
• Standard cutoff: >500 ng/mL = positive
• A negative D-dimer in a low-probability patient excludes proximal DVT with ~92% sensitivity
• Age-adjusted threshold: Age × 10 ng/mL - safely reduces need for ultrasound in elderly patients while maintaining ~95% sensitivity
• D-dimer specificity is low in pregnancy, cancer, infection, recent surgery, and inflammatory states
• A negative D-dimer in a high-probability patient does not exclude DVT - imaging is still required

Step 3: Venous Compression Ultrasound (VCU/Doppler)

• Non-compressibility of the vein under probe pressure (most reliable sign)
• Absent or abnormal flow on Doppler
• Absence of flow augmentation with calf compression
• Absent respiratory phasicity
• Direct visualization of intraluminal thrombus

Other Imaging

• CT venography: Used in suspected pelvic or IVC thrombosis
• MRI venography: Excellent for pelvic veins, pregnancy, or when ultrasound is inconclusive
• Conventional contrast venography: Historical gold standard, now rarely used due to invasiveness

Treatment

Anticoagulation - First-Line Therapy

• Rivaroxaban (Factor Xa inhibitor) and Apixaban (Factor Xa inhibitor) - do NOT require bridging with LMWH; first-choice anticoagulants for most DVT patients
• Dabigatran (direct thrombin inhibitor) - requires initial LMWH bridge for 5-10 days
• DOACs are equally effective as warfarin in preventing recurrent VTE but are associated with fewer bleeding complications, especially fewer intracranial bleeds
• Do not require regular INR monitoring; well-tolerated by patients

• Subcutaneous injection; treatment dose initiated immediately
• Preferred initial therapy for cancer-associated DVT (DOACs increasingly used here too)
• Preferred in pregnancy (does not cross the placenta)
• Adjust or avoid in significant renal impairment (use unfractionated heparin instead)

• IV infusion; used in severe renal impairment or when rapid reversal may be needed
• Requires aPTT monitoring

• Fondaparinux (indirect Factor Xa inhibitor)
• Bivalirudin (direct thrombin inhibitor)
• Argatroban

• Provoked DVT (transient risk factor, e.g., surgery): minimum 3 months
• Unprovoked DVT: At least 3 months; often extended based on recurrence risk vs. bleeding risk
• Cancer-associated DVT: Indefinite (as long as cancer is active)
• Recurrent DVT or major thrombophilia: Often indefinite

Anticoagulant Reversal Agents

IVC Filter

Endovascular Interventions (Catheter-Directed Thrombolysis / CDT)

• Increasingly used in acute iliofemoral DVT with symptoms ≤14 days duration
• Goals: restore venous patency, relieve acute symptoms, reduce risk of post-thrombotic syndrome
• Techniques include: catheter-directed thrombolysis (CDT), pharmacomechanical thrombectomy, venoplasty, and stenting
• Systemic thrombolysis for DVT (without concurrent limb ischemia) has not been shown to improve mortality or reduce post-thrombotic syndrome and increases bleeding risk - not routinely recommended
• Selected patients with massive iliofemoral thrombosis or threatened limb viability may benefit [Rosen's Emergency Medicine, p. 1201; Bailey & Love's Surgery, p. 5666; Fuster & Hurst's The Heart, p. 3307]

Compression and Ambulation

• Compression stockings: No longer routinely recommended to prevent post-thrombotic syndrome (recent evidence does not consistently support this benefit). However, some patients report quality-of-life improvement, and timing of initiation may matter.
• Early ambulation after starting anticoagulation is encouraged - it reduces the incidence of post-thrombotic syndrome. [Rosen's Emergency Medicine, p. 1201]

DVT Prophylaxis

• Mechanical: Graded compression stockings (TED stockings), intermittent pneumatic compression (IPC) devices / calf pumps
• Pharmacological: Subcutaneous LMWH (e.g., enoxaparin), UFH, fondaparinux
• Compression stockings are contraindicated in peripheral arterial disease, peripheral neuropathy, severe oedema, or skin breakdown

Complications

1. Pulmonary Embolism (PE)

2. Post-Thrombotic Syndrome (PTS)

• Chronic leg pain, heaviness, and fatigue
• Persistent edema
• Paresthesia, induration
• Skin discoloration (lipodermatosclerosis)
• Varicose veins
• In severe cases: venous stasis ulcers Early endovascular intervention for iliofemoral DVT may reduce the risk of PTS. [Rosen's Emergency Medicine, p. 1201; Bailey & Love's Surgery, p. 5166]

3. Venous Gangrene / Phlegmasia

4. Recurrent VTE

Special Populations

Pregnancy

• DVT is more common in pregnancy due to IVC compression by the gravid uterus (especially left-sided), hormonal hypercoagulability, and venous stasis
• LMWH is the preferred anticoagulant - does not cross the placenta
• Warfarin and DOACs are contraindicated in pregnancy
• Use the LEFt score for clinical probability assessment
• Anticoagulate until at least 6 weeks postpartum (total duration minimum 3 months)

Cancer Patients

• Cancer is both a risk factor and a trigger for DVT investigation (unprovoked DVT should prompt malignancy screening)
• LMWH was historically preferred; DOACs (especially apixaban and rivaroxaban) are increasingly first-choice for cancer-associated VTE based on recent trial data
• Duration: indefinite while cancer is active

Upper Extremity DVT

• 90% associated with indwelling central venous catheters, pacemaker wires, or infusion devices

• Paget-Schroetter syndrome: effort-induced subclavian vein thrombosis in young athletes (dominant arm)
• Treat with anticoagulation; consider catheter removal if possible

Summary Algorithm

Suspected DVT
    ↓
Calculate Wells Score
    ↓
Low probability (≤1)         High probability (≥2)
    ↓                              ↓
D-Dimer                      Venous Ultrasound
    ↓                              ↓
Negative → DVT excluded    Positive → Diagnose DVT
Positive → Ultrasound      Negative → D-Dimer
                                ↓
                        If D-Dimer negative → DVT excluded
                        If D-Dimer positive → Repeat US in 1 week
                                ↓
                           Initiate anticoagulation
                           (DOAC preferred, or LMWH)
                           Duration ≥3 months

Key Teaching Points

1. DVT is often clinically silent - most cases are asymptomatic; a high index of suspicion based on risk factors is required
2. Virchow's Triad (stasis, endothelial injury, hypercoagulability) underlies all DVT pathogenesis
3. Wells score + D-dimer is the validated diagnostic pathway; venous ultrasound non-compressibility is the gold standard imaging sign
4. DOACs (rivaroxaban, apixaban) are now first-line treatment for most patients with DVT - no bridging required, fewer bleeds than warfarin
5. The most life-threatening complication is PE; the most common chronic complication is post-thrombotic syndrome (20-50% of patients)
6. LMWH is preferred in pregnancy and renal failure patients (use UFH in severe renal impairment)
7. IVC filter is a bridge for patients who cannot be anticoagulated
8. Early ambulation after anticoagulation reduces post-thrombotic syndrome

Guillain-Barré Syndrome (GBS) - Comprehensive Medical Overview

Definition

1. Acute onset
2. Cytoalbuminologic dissociation in cerebrospinal fluid (elevated protein with low cell count)
3. Monophasic course (one episode that progressively worsens then typically recovers)

Historical Background

Epidemiology

• Annual incidence: 0.81 to 1.89 cases per 100,000 persons per year worldwide
• Sex: Men more commonly affected than women (ratio ~1.4:1)
• Age: Incidence increases with age, though it affects all age groups
• Most common form: Acute Inflammatory Demyelinating Polyradiculoneuropathy (AIDP) accounts for ~97% of cases in North America and Europe
• Preceding infection: Identified in ~60-70% of patients, typically 1-4 weeks before neurological symptoms
• ICU admission: Required in 20-30% of patients due to respiratory failure; mortality rises to ~14.3% in mechanically ventilated patients
• GBS and COVID-19: Not substantially associated with SARS-CoV-2 infection or most vaccines; a slight increase of 0.6 cases/100,000 doses was noted with ChADOx1nCoV-19 (AstraZeneca). GBS incidence actually declined during the pandemic due to reduced exposure to common triggering infections.
• Zika virus: Significantly increased risk of all GBS variants

Subtypes and Classification

Common Subtypes

Rare Variants

Pathophysiology

Molecular Mimicry - The Core Mechanism

• A preceding infection (most commonly Campylobacter jejuni) presents antigens structurally similar to ganglioside components of peripheral nerve myelin or axolemma
• T cell-mediated responses and antibody-mediated responses both contribute, though T cells are believed to play the dominant role
• The injury is most extensive at nerve roots and proximal nerve segments
• Mononuclear cell infiltrates rich in macrophages mediate myelin stripping in AIDP

Specific Antibody-Target Associations

Infectious Triggers

Clinical Features

Typical Presentation (AIDP)

1. Prodrome (1-4 weeks prior): Respiratory tract infection, gastroenteritis, or other illness
2. Neurological phase: Rapidly progressive weakness, usually ascending

Key Clinical Features

• Ascending, symmetrical flaccid weakness - the hallmark
• Areflexia or hyporeflexia - almost universal and required for diagnosis
• Proximal weakness is common (not just "ascending from distal")
• 5% have isolated cranial nerve involvement that then descends
• Respiratory failure in 20-30% due to diaphragm and intercostal muscle weakness

• Mild sensory loss or paresthesias in most patients
• Sensory symptoms typically less prominent than motor weakness
• Neuropathic/deafferentation pain is common - truncal in distribution, severe, responds better to anticonvulsants than opiates

• Bilateral facial nerve (CN VII) palsy in ~50% of patients
• Bulbar weakness: dysarthria, dysphagia (risk of aspiration)
• Ophthalmoplegia (especially in Miller-Fisher variant)
• Ptosis

• Cardiac arrhythmias (most dangerous - can cause sudden death)
• Blood pressure lability (hypertension and hypotension)
• Uncontrolled sweating
• Temperature dysregulation
• Ileus and bladder dysfunction
• Orthostatic hypotension
• Dysautonomia is a major source of ICU morbidity and can cause sudden cardiac arrest

• Ophthalmoplegia (bilateral external ophthalmoplegia)
• Ataxia (cerebellar-type)
• Areflexia
• Facial weakness, ptosis, and pupillary abnormalities may also be present
• Nerve conduction velocities are normal (unlike AIDP)

Time Course

Day 0-14:      Infection/trigger
Week 1-2:      Symptom onset - weakness, sensory symptoms
Weeks 2-4:     Progressive worsening - NADIR of disease
               50% reach maximum disability within 2 weeks
               75% within 3 weeks
               >90% within 4 weeks
               [5% progress to maximal loss within 72 hours!]
Week 4+:       Plateau phase
Weeks 4-8:     Beginning of recovery (spontaneous remyelination)
Months-Years:  Full recovery (variable, may be prolonged)

Diagnostic Criteria

Required Features (Brighton Collaboration Criteria / Asbury & Cornblath)

1. Progressive weakness of both legs and arms (bilateral)
2. Areflexia or significant hyporeflexia

Supportive Clinical Features

• Progression over days to 4 weeks
• Relative symmetry of symptoms and signs
• Mild sensory symptoms or signs
• Bifacial palsies
• Autonomic dysfunction
• Absence of fever at onset (fever suggests alternative diagnosis)
• Recovery beginning 2-4 weeks after progression ceases

Laboratory Features Supportive of Diagnosis

• Cytoalbuminologic (albuminocytologic) dissociation: elevated protein (often >45 mg/dL) with <10 WBCs/μL - this is the classical CSF finding
• CSF protein may be normal in the first 7-10 days of illness (up to 10% remain normal throughout)
• CSF WBC >50/μL should prompt evaluation for HIV seroconversion, Lyme disease, or meningitis - these suggest an alternative diagnosis

• Anti-GQ1b: >85% sensitivity for Miller-Fisher syndrome
• Anti-GM1, anti-GD1a: AMAN subtype
• Helpful for classification but not required for treatment initiation

Differential Diagnosis

Management

Hospitalization and Monitoring

• Severity of limb weakness
• Timing of symptoms at presentation
• Bulbar symptoms

Specific Immunotherapy

1. Intravenous Immunoglobulin (IVIG) - Preferred

• Dose: 2 g/kg total, divided over 2 days (or longer if cardiac function or fluid status requires it)
• Mechanism: Suppresses immune responses through multiple mechanisms including Fc receptor blockade, complement inhibition, modulation of T and B cell function
• Preferred over plasmapheresis because patients are significantly more likely to complete a full course
• A second dose of IVIG does not improve outcomes and increases complication risk - do not repeat

2. Therapeutic Plasma Exchange (Plasmapheresis) - Equally Effective

• 5 plasma volumes exchanged over 10 days
• Removes circulating autoantibodies and inflammatory mediators
• Equally effective to IVIG (no randomized trial has shown superiority of either)
• Many physicians try them sequentially if the first treatment fails
• Less preferred because it requires vascular access and more patient compliance

3. Corticosteroids - NOT Recommended

• Methylprednisolone 500 mg/day for 5 days plus IVIG shows a slight initial advantage but no long-term benefit over IVIG alone
• Steroids alone do not improve outcomes
• Given the risks, corticosteroids are generally not recommended for GBS

4. Newer Agents

• Interferon has not been shown to improve outcomes
• Newer immune modulation drugs (e.g., eculizumab, IgG-Fc receptor blockers) are currently in clinical trials

ICU and Supportive Care

Prognosis

• Older age
• Preceding diarrheal illness (C. jejuni infection)
• Axonal variant (AMAN/AMSAN)
• Need for mechanical ventilation (mortality increases to ~14.3%)
• Reduced CMAP amplitudes in the upper extremities (significant axonal loss)
• Presence of anti-GM1 antibodies
• Severity of weakness at nadir

• Young age
• Respiratory and upper limb infection as trigger (vs. diarrheal illness)
• Demyelinating pattern (AIDP - remyelination is more complete)
• Milder weakness at presentation
• Anti-GQ1b antibodies (MFS has excellent prognosis)

Comparison: GBS vs. CIDP

Summary: Key Teaching Points

1. GBS is the most common cause of acute flaccid paralysis worldwide in the post-polio era
2. The classic CSF finding is cytoalbuminologic dissociation (high protein, <10 WBCs) - but may be normal in the first 7-10 days
3. Areflexia is virtually universal and required for diagnosis
4. Respiratory failure occurs in 20-30% - monitor FVC closely; don't wait for hypercarbia
5. IVIG (2 g/kg) is the preferred treatment - equally effective to plasmapheresis but better tolerated; start within 2 weeks of onset
6. Corticosteroids do not help in GBS (contrast with CIDP where they work)
7. Autonomic dysfunction (in 65%) is life-threatening - continuous cardiac monitoring is mandatory
8. Succinylcholine is absolutely contraindicated - risk of fatal hyperkalemia
9. Anti-GQ1b antibodies are highly specific for Miller-Fisher syndrome
10. Pain (deafferentation) is common, severe, and responds to anticonvulsants better than opioids
11. Most patients recover, but 20% are left with significant disability; axonal subtypes have worse outcomes