Deep vein thrombosis overview

# Overview
Deep vein thrombosis (also known as deep venous thrombosis or DVT and colloquially referred to as economy class syndrome) is the formation of a blood clot ("thrombus") in a deep vein. The risk is significantly increased if the thrombus embolizes to the lungs, causing pulmonary embolism. Occasionally, veins in the arm are also affected (known as Paget-Schrotter disease). Upper extremity DVT is less common but also may lead to PE, especially in the presence of a venous catheter. Thrombophlebitis is swelling (inflammation) of a vein caused by a blood clot. Venous thromboembolism (VTE) is a hypernym which includes Deep venous thrombosis (DVT) and pulmonary embolism (PE). It is a major public health problem and one of the most common cause of preventable cause of death in hospital patients. It is the third most common cardiovascular disorder after coronary artery disease and stroke. It is frequently underestimated and misdiagnosed and  failure to provide adequate prophylaxis and therapy can be fatal for the patient.

# Classification
Deep vein thrombosis (DVT) is classified based on the site of occlusion or clot formation. Symptom presentation and complication is largely influenced by location of the embolus.

# Pathophysiology
Venous thrombosis is composed of three mechanisms, collectively described as the Virchow's triad: 1. Alterations in blood flow (stasis): Venous stasis is a major risk factor for the development of thrombosis. It occurs in certain pathological conditions (as in heart failure) wherein it causes an increase in platelet to endothelium contact and decreases the dilution of clotting factors. This increases the risk of clot formation, and it forms microthrombi, which further grow and propagate. 2. Injury to the vascular endothelium (Endothelial dysfunction): Intrinsic or secondary to external trauma, such as catheterization, can cause intimal damage and stimulate clot formation. 3. Alterations in the constitution of blood (Hypercoagulability): Abnormal changes in coagulation can increase the propensity to develop thrombosis.

# Differentiating Deep Vein Thrombosis from Other Diseases
Only 25% of the patient evaluated for deep vein thrombosis (DVT) have the disease. DVT is characterized by pain and swelling of the limb, which is not specific. Numerous patients with DVT are asymptomatic.

# Epidemiology and Demographics
In the United States, approximately 350,000 to 600,000 new cases of venous thromboembolism are diagnosed each year. The incidence of deep vein thrombosis is estimated to be 100 cases per 100,000 persons per year. Deep vein thrombosis accounts for two-thirds of all venous thromboembolism cases. Mortality and complications from deep vein thrombosis are high: one-third of the patients develop post-thrombotic syndrome and another 30% have recurrent DVT within 10 years. In the United States, deep vein thrombosis accounts for approximately 100,000 deaths each year.

# Risk Factors
The identification and minimization of risk factors is important in the management of DVT.  The duration of anticoagulation is guided by the presence of thrombophilic risk factors.

# Natural History, Complications and Prognosis
Thrombus formation typically begins in the calf veins and naturally progresses to the proximal veins and ultimately, breaks free from the site formation and travels to the pulmonary artery where it is called a pulmonary embolism. In many cases, patients with a thrombus can be asymptomatic until it progresses into the proximal veins.

# Diagnosis

## Pretest Probability
In a patient with suspected DVT, establishing pre-test probability helps in early risk stratification and appropriate use of laboratory tests and imaging modalities. Many pretest probability scoring systems are proposed for use in primary care patients, like the Wells score, Hamilton score , and AMUSE score.  When combined with pretest probability, ultrasonography and D-dimer tests are most useful in a diagnosis for DVT.

## History and Symptoms
A proper history and physical exam is very important for establishing an accurate diagnosis of DVT or VTE. One of the first steps in the management of DVT is the determination of the Wells score for DVT. Out of the 10 clinical questions in the score, 9 can be ascertained solely on the basis of history and physical exam. This underscores the importance of these variables. A high index of suspicion is also necessary to diagnose DVT.

## Physical Examination
The physical examination may be completely normal in patients with DVT. A high degree of suspicion is necessary for early identification of venous thrombosis, as sometimes these patients are admitted with a different complaint and a thorough physical exam gives a clue to the diagnosis.

## Laboratory Findings
The lifetime incidence of DVT ranges from 2-5% in the general population. It accounts for a large number of ER visits and puts the patient at-risk for a life-threatening pulmonary embolism. The use of D-dimer after assessment of pre-test probability has been widely validated now and has led to a significant reduction in unnecessary procedures in the ER and hospital settings. This chapter will review the role of D-dimer in diagnosis of DVT. For a detailed discussion on D-dimer, please visit D-dimer.

## Ultrasound
Venous ultrasound is the confirmatory test for diagnosis of DVT. The most common form is compression ultrasonography, which assesses the compressibility of femoral and popliteal veins. Diagnosis of DVT is established if the vein can not be collapsed under gentle ultrasound probe pressure. In most cases, it is performed in the proximal veins, as the risk of pulmonary embolism is much higher with that. Whole-leg ultrasound examines the deep veins of the proximal leg and calf, and it is used in cases where distal DVT is suspected. Iliac vein ultrasound may be performed, if thrombosis is suspected (e.g.: Pregnant women with swelling of the whole leg).

## Venography
Venography is the "gold standard" to diagnose venous thrombosis, however it is not the preferred test in clinical settings. It includes injection of contrast into the dorsal foot vein and checking for a intraluminal filling defect that is present in more than one view.

## CT
Venous thrombosis in the proximal deep veins is responsible for more than 90% of the pulmonary embolisms. Some of the investigators have suggested combined use of CT PE protocol and CT scan venography in cases of suspected DVT and PE.

## MRI
MRI can also be used for the diagnosis of venous thrombosis, however it is usually not applied as a first test because of cost and inaccessibility.

## Other Imaging Findings
A number of invasive and non-invasive approaches are possible.

## Specific Situations
The approach to diagnosis of DVT may be modified in certain situations, where the suspicion is high or there is a recurrent episode. This chapter will discuss these modifications that have been recommended to the American College of Chest Physicians.

# Treatment

## Medical Therapy
An approach to the treatment of DVT has been described here. The primary purpose of treatment is to prevent the
further clot extension, acute pulmonary embolism, recurrence of thrombosis, prevention of late complications such as post-thrombotic syndrome and chronic thromboembolic pulmonary hypertension.

## Primary Prevention
Primary prevention includes the strategies that help to avoid the development of disease. Awareness of Deep venous thrombosis is the best way to prevent this condition.

## Secondary Prevention
The U.S. Preventive Services Task Forces describes secondary prevention measures as those that identify and treat asymptomatic persons who have already developed risk factors or preclinical disease but in whom the condition is not clinically apparent. Clinical practice guidelines by the American College of Chest Physicians (ACCP) provide recommendations on DVT prophylaxis in hospitalized patients.

## Landmark Trials
Landmark trials have compared different formulations and routes of antithrombin administration to treat and prevent deep vein thrombosis.