Venous Thrombosis

Published on 10/02/2015 by admin

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71 Venous Thrombosis

D. Mark Courtney

• Distinction between symptoms of chronic venous disease and acute deep vein thrombosis (DVT) can be difficult. Careful attention to the time course of symptoms as reported by the patient and scrutiny of the medical record may reveal that the symptoms are less likely to be acute.

• The D-dimer blood test can be useful in the evaluation of potential DVT. Just as with pulmonary embolism, its use and interpretation need to take into account the pretest probability of disease.

• Many patients may not have classic, obvious risk factors for DVT but may still have the disease.

• The lack of 24-hour availability of duplex ultrasound, the imaging method of choice for DVT, requires a clear estimate of the probability of disease, the likelihood and timing of follow-up, and consideration of the risks and benefits of temporary empiric anticoagulation.

• Follow-up of patients is critical for monitoring the anticoagulation effects of warfarin, evaluation of progression of symptoms, and determination of the duration of anticoagulation.

Epidemiology

Deep vein thrombosis (DVT) is a common diagnosis that may be seen in emergency department (ED) patients with minimal to no symptoms or with obvious findings on examination. DVT most typically arises in the lower part of the leg and may exist in combination with or as a precursor to pulmonary embolism (PE). Together, DVT and PE are termed venous thromboembolism (VTE). Understanding VTE as a single disease is useful because risk factors, urgency in establishing a diagnosis, and treatment are similar for both PE and DVT. The annual incidence of DVT has been estimated to be 92 cases per 100,000 persons, and the rate steadily advances with increased age (32/100,000 in persons younger than 55 years, 282/100,000 in those 65 to 74 years of age, and 553/100,000 in those 75 years or older).¹

Pathophysiology

DVT can occur in both young and old patients and may result in both acute and chronic morbidity. It may be acute and life- or limb-threatening (PE, total iliofemoral obstruction) or can lead to chronic and debilitating complications (postphlebitic syndrome, venous stasis and ulceration, recurrent DVT).

Typical DVT risk factors are summarized by the Virchow triad: trauma, stasis, and hypercoagulability. These risk factors are the same as for PE (Table 71.1). However, 25% to 50% of patients with DVT may have no identifiable risk factor known at the time of evaluation.

Table 71.1 Known Risk Factors for Acute Deep Vein Thrombosis

RISK FACTORS	SPECIFIC NOTES
Previous history of PE or DVT	Inquire about the setting and circumstances of the previous VTE
Recent trauma or surgery	In general, trauma requiring admission or surgery requiring general anesthesia within the previous month. Recent long-bone, vascular, or trauma surgery may especially increase the risk
Cancer	In general, patients with currently treated cancer or palliative care
Central or long-term vascular catheters
Age	Risk significantly increases above the age of 50 to 60 years
Oral contraceptives	Especially third-generation formulations
Hormone replacement therapy	Currently less common than in the past
Pregnancy	Risk increases along with the duration of pregnancy; it peaks at term and then decreases over a period of 4 to 6 weeks postpartum
Immobility	Includes casts or splints, as well as permanent limb or generalized body immobility, including that from general hospitalization
Factor V Leiden mutation	Most common in northern European populations. The heterozygous carrier state exists in 3% to 7% of many samples. A homozygous mutation is less common and confers three times greater risk for VTE relative to the normal genotype.
Antiphospholipid antibody syndrome	Very potent risk factor. Associated with large and recurrent PE. May be associated with anticardiolipin antibodies, stroke, myocardial infarction, and frequent first-trimester miscarriages
Prothrombin mutation
Hyperhomocysteinemia	Can occur as a result of inadequate folate and B vitamin intake, as well as a genetic mutation in methyltetrahydrofolate reductase. The degree of elevation in risk is controversial
Deficient levels of clotting factors	Protein C, protein S, antithrombin III
Congestive heart failure	May result from generalized immobility or vascular stasis
Chronic obstructive pulmonary disease	May result from generalized immobility
Air travel	Primary risk with travel in excess of 5000 km (3100 miles) and concurrent other risk factors. The degree of elevation in risk is controversial
Obesity	The degree of elevation in risk is controversial

The timing of development of DVT is difficult to know, but it typically starts with small asymptomatic abnormalities in flow at the level of the endothelium. It may be precipitated by venous valve dysfunction or immobility, both of which decrease the normal function of the venous-muscle pump system for return of blood from the legs.

DVT can also develop in the pelvic veins (typically associated with comorbid pelvic or gynecologic conditions) or upper extremity (typically with venous catheters), but by far most cases of DVT diagnosed in the ED are in the legs.

Understanding the venous anatomy of the leg is crucial for interpreting risk and diagnostic tests. The most obvious and concerning cases of DVT occur in the proximal deep system. In order from distal to proximal, the proximal deep veins are the popliteal, femoral, deep femoral, common femoral, and finally the external iliac. Occasionally, the femoral vein is referred to as the superficial femoral vein, which results in confusion because it is a deep vein and clots there should be treated as DVT. Thrombosis may develop in the distal deep system (the calf), and these veins are the anterior tibial, the posterior tibial, and the peroneal. These are deep veins and thrombosis here is DVT, but management of isolated distal DVT is somewhat less certain than that for proximal DVT. Finally, the superficial venous system of the leg can be subject to thrombosis and superficial thrombophlebitis, but this is managed differently from thrombosis in the deep system. These veins are the lesser and greater saphenous and the perforating veins. This is not DVT, and isolated thrombosis here is not typically treated with systemic anticoagulation.

The morbidity associated with venous thrombosis is not just due to subsequent embolization. Even with anticoagulation there is the possibility of injury to the endothelium and venous valve system, both of which can result in chronic venous stasis and recurrent clots.

Presenting Signs and Symptoms

Patients can have a variety of symptoms that may include fullness, cramping, achiness, or vague pain in the calf or posterior part of the leg. They may also report swelling. It is important to distinguish between unilateral symptoms, which may be more likely to be due to DVT, and bilateral symptoms, which may be more likely to be a consequence of some other disease process. The exception would be the rare case of obstruction of the inferior vena cava or simultaneous bilateral DVT. Signs on examination may include edema, redness, and tenderness, particularly in the posterior aspect of the calf or the upper part of the leg.

Swelling may be minimal or extensive and involve the entire extremity. It can be challenging to distinguish chronic symptoms of venous stasis from acute DVT based on a single examination. Therefore, a careful history to establish the time course of the findings in the leg is critical, and examination of the past medical record can be highly valuable.

Use of examination alone to determine the presence or absence of DVT is problematic. Classic teaching is that the accuracy of physical examination alone for the diagnosis of DVT is 50%. This is a bit of a generalization, but it is clear that findings may be subtle, patients may not have detectable tenderness or edema early in the course or spectrum of disease severity, and some patients may be nearly asymptomatic. The often mentioned, but rarely understood or performed Homan sign—calf pain elicited by passive dorsiflexion of the ankle—is insensitive, nonspecific, and useless.

Differential Diagnosis and Medical Decision Making

Many other diseases may be accompanied by pain, swelling, and tenderness of the leg. Box 71.1 presents a differential diagnosis of conditions that should be considered.

Clinicians often have a difficult time distinguishing between cellulitis and DVT. The pain, swelling, erythema, and unilateral nature of cellulitis may be clinically similar to findings in patients with DVT, and the two conditions can even coexist. A break in the skin, fever, or warmth may more strongly suggest cellulitis. However, distinguishing between the two may be impossible without objective testing for DVT.

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