Deep vein thrombosis
Deep vein thrombosis (DVT) is a form of venous thromboembolism which occurs in deep veins, most commonly in the legs or groin. Its main importance is the risk of the deep venous thrombosis dislodging and traveling to the lungs, causing pulmonary embolism (PE). DVT mostly affects the distal deep veins, but may affect the larger, proximal veins as well, including the iliac, femoral, or popliteal veins. PE is a serious complication which can lead to death in 30 – 60% of cases, and is more common in case of proximal DVT.
Etiology
Clinical features
DVT presents as a unilaterally swollen leg which is warm and erythematous. The leg may be tender or painful. Homans sign refers to calf pain on dorsiflexion of the foot, which may be positive in case of DVT. In distal DVT, symptoms are confined to the calf. Proximal DVT may cause symptoms of the whole leg.
Upper extremity DVT is rare and usually due to central catheters or cancer.
Diagnosis and evaluation
When DVT is suspected, we calculate the pre-test probability of DVT to determine how to proceed. The pre-test probability of DVT can be calculated with the Wells score:
| Item | Points |
|---|---|
| Active or recent cancer | + 1 |
| Paralysis or recent cast | + 1 |
| Recent bed rest or surgery | + 1 |
| Pain on palpation of deep veins | + 1 |
| Swelling of entire leg | + 1 |
| Diameter difference compared to other calf of > 3 cm | + 1 |
| Pitting oedema on affected side only | + 1 |
| Dilated superficial veins on affected side | + 1 |
| Alternative diagnosis at least as probably as DVT (cellulitis, Baker cyst, etc.) | – 2 |
If the Wells score is 0, the pre-test probability is low (3%). If 1 – 2, the probability is intermediate (17%). If 3 or more, the probability is high (> 50%). The Wells score is then used to guide further evaluation.
- Wells score 0
- -> measure D-dimer
- D-dimer negative: DVT excluded
- D-dimer positive: perform ultrasound
- -> measure D-dimer
- Wells score 1 – 2
- -> perform ultrasound
- Ultrasound negative: measure D-dimer
- Ultrasound positive: diagnostic of DVT
- -> perform ultrasound
D-dimer is a fibrin degradation product. Its level in the blood correlates with the activity of coagulation and fibrinolysis. It’s highly sensitive for VTE and DIC, in which case the level is increased., D-dimer is not specific. It can be elevated due to other conditions, like pregnancy, cancer, infection, kidney disease, surgery, etc. Thus, D-dimer is used to rule out VTE (if the pre-test probability is low), rather than diagnose it. If D-dimer is normal, VTE is effectively ruled out (high negative predictive value). It should not be measured in those with conditions known to cause positive D-dimer.
Ultrasound is important in the evaluation of DVT. It may show the thrombus as a hyperechoic mass in the venous lumen. When applying pressure to the vein with the ultrasound probe, an obstructed vein will not be compressible. Doppler imaging may show absent blood flow. If these findings are present, the diagnosis of DVT is made.
If D-dimer and ultrasound are inconclusive, venography with CT or MRI may be used.
Patients with VTE without clear risk factors, especially if recurrent, should be considered for screening for a hypercoagulable state (thrombophilia) and malignancy.
Treatment
DVT should be treated with anticoagulants for 3 months, preferably DOACs like rivaroxaban or apixaban. Very low-risk patients with distal DVT may be managed with regular surveillance rather than anticoagulants, but in almost all cases patients with DVT should receive anticoagulant therapy.
After three months, the patient should be reassessed for whether they require longer therapy. If the underlying risk factor(s) which are suspected to have caused the DVT are irreversible, indefinite anticoagulant therapy may be appropriate. If the risk factor(s) was reversible and is now reversed, anticoagulant therapy should be stopped after these three months.
If anticoagulants are contraindicated, IVC filters may be used. These filters are placed in the IVC and aim to prevent embolisms from reaching the heart and lungs.
Complications
- Pulmonary embolism
- Post-thrombotic syndrome
- Phlegmasia cerulea dolens
Phlegmasia cerulea dolens is a severe form of DVT where all veins of one extremity is obstructed, leading to necrosis. It’s an emergency with high mortality, which causes severe swelling, pain, cyanosis, and pulselessness. It requires emergency thrombectomy surgery to prevent shock, gangrene, and limb loss.