Venous thromboembolism classification based on cause

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VTE Classification Based on Cause

Venous thromboembolism (VTE) - encompassing deep vein thrombosis (DVT) and pulmonary embolism (PE) - is classified by cause into three broad etiologic categories, which in turn feed into two clinical categories (provoked vs. unprovoked).

I. Etiologic Classification

1. Hereditary (Inherited) Causes - Thrombophilia

These are genetic defects that either increase procoagulant activity (gain of function) or reduce natural anticoagulant activity (loss of function):

Loss-of-Function Mutations (reduced anticoagulation):

Disorder	Notes
Antithrombin deficiency	Rare (~1/2000); can be quantitative or qualitative; heparin resistance
Protein C deficiency	Liver-synthesized; vitamin K-dependent; activates fibrinolysis
Protein S deficiency	Cofactor for activated protein C

Gain-of-Function Mutations (increased coagulation):

Disorder	Notes
Factor V Leiden	Most common inherited thrombophilia (~5% of whites); autosomal dominant; 5x VTE risk (heterozygous)
Prothrombin gene mutation (G20210A)	Second most common (~3% in whites); elevates prothrombin levels
Elevated factor VIII, IX, or XI levels	High heritability; factor VIII also raises arterial risk

Suggested by: VTE at age <50 years, unprovoked/recurrent VTE, family history, thrombosis in unusual anatomic locations (mesenteric, portal, cavernous sinus veins).

2. Acquired Causes

These develop during life and create a hypercoagulable state:

Category	Examples
Demographic/lifestyle	Advanced age, obesity, previous VTE
Malignancy	Active cancer (especially metastatic) - highest risk group
Immobility	Prolonged bed rest, long-haul travel, paralysis
Surgery/trauma	Major orthopedic, neurosurgery, polytrauma (highest surgical risk)
Medications	Estrogen (OCP, HRT), L-asparaginase, heparin (HIT)
Pregnancy/puerperium	6x baseline risk; puerperium intermediate risk
Autoimmune	Antiphospholipid syndrome (APS), HIT
Systemic disease	Nephrotic syndrome, collagen vascular diseases, infection, DIC
Hematologic	Paroxysmal nocturnal hemoglobinuria (PNH), myeloproliferative disorders (JAK2 mutation)

3. Mixed (Both Hereditary and Acquired)

Condition	Notes
Hyperhomocysteinemia	Can arise from MTHFR mutation + folate deficiency; both arterial and venous risk. (Note: MTHFR mutation alone without elevated homocysteine does NOT cause VTE)

II. Clinical Classification: Provoked vs. Unprovoked

This classification drives treatment duration decisions:

Category	Definition	Recurrence Risk (after stopping anticoagulation)
Provoked	VTE triggered by an identifiable transient or persistent risk factor (surgery, trauma, cancer, immobility, estrogen)	~5% per year
Unprovoked (idiopathic)	No clear precipitating factor identified	~15% per year

Important nuances:

Active cancer is a persistent provoking factor (unlike surgery, which is transient)
The 2019 ESC guidelines moved away from this binary classification toward individualized risk scoring, because "provoked" VTE with enduring risk factors can have recurrence risk comparable to "unprovoked" VTE
Unprovoked VTE overall has a ~30-40% chance of recurrence within 10 years after stopping anticoagulation

The Thrombosis Threshold Model

The following diagram from Braunwald's illustrates how these causes interact - hereditary and acquired factors combine to build an intrinsic risk, which is then tipped over the threshold by triggering events:

Thrombosis threshold model showing hereditary risk factors (antithrombin deficiency, protein C/S deficiency, Factor V Leiden, prothrombin gene mutation) and acquired risk factors (advanced age, previous VTE, cancer, obesity) combining to create intrinsic thrombosis risk, further increased by triggering factors (surgery, immobilization, pregnancy, estrogens) to exceed the thrombosis threshold

Risk Stratification by Level of Risk

Risk Level	Examples
Highest	Major orthopedic surgery, neurosurgery, polytrauma, metastatic cancer
Intermediate	Prolonged bed rest, antiphospholipid antibodies, puerperium
Mild	Pregnancy, obesity, long-distance travel, oral contraceptives, HRT

Sources: Braunwald's Heart Disease (Table 95.1, Fig. 95.9) | The Washington Manual of Medical Therapeutics | Tintinalli's Emergency Medicine | Braunwald's Heart Disease (anticoagulation duration section)

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