DVT (Deep Vein Thrombosis)

DVT (Deep Vein Thrombosis)

How to investigate and treat DVT (Deep Vein Thrombosis) – for doctors, medical students and medical exams

 

Types of deep vein thrombosis

  • Most deep vein thromboses (DVTs) occur in a leg. These are divided into:
    • Above-knee (proximal) DVT if present in the popliteal, superficial femoral (despite the name, still a deep vein), deep femoral, common femoral or external iliac veins
    • Below knee (distal) DVT if present in the soleal or peroneal veins
  • DVT can also more rarely affect an arm.
  • Note thromboses in the saphenous veins or other superficial veins are not DVTs
  • ‘Venous thromboembolism’ (VTE) is used to collectively refer to DVT and pulmonary embolism (PE).

 

Epidemiology of deep vein thrombosis

 

Click here for all the causes of deep vein thrombosis

 

Prevention of deep vein thrombosis

 

Presentations of DVT

  • History
    • Unilateral leg pain and/or swelling, usually of insidious onset
    • Symptoms may be confined to the calf or the thigh, or affect the whole leg
    • The location of symptoms is an unreliable guide to the location of the thrombus
    • May be asymptomatic (incidental finding)
    • Ask about symptoms of pulmonary embolism
    • Bilateral leg swelling is very rarely due to DVT – only if clot has extended around the iliac bifurcation to the other leg, or in the context of pulmonary embolism and right heart failure.
    • Rarely presents with fever or sweats
  • Examination findings
    • Swelling, often tender
    • Pitting oedema
    • Redness
    • Dilated collateral veins (not varicose veins)
    • Evidence of the primary cause:
      • Inguinal lymphadenopathy
      • Inguinal sinus / discharging abscess from intravenous drug abuse
      • Abdominal mass
    • Signs of pulmonary embolism
      • Tachycardia
      • New atrial fibrillation
      • Dullness and reduced breath sounds if pulmonary infarction

 

Video overview of DVT

 

Differential diagnosis of deep vein thrombosis

  • Ruptured Baker’s cyst (though may co-exist with DVT)
  • Cellulitis
  • Lymphoedema
  • Asymmetric oedema due to cardiac failure or renal failure
  • Muscle haematoma

 

Scoring of deep vein thrombosis

Active cancer+1
Recently bedridden ≥3 days or major surgery in the past 12 weeks+1
Paralysis, paresis or recent plaster immobilization of affected leg+1
Previously documented DVT+1
Calf swelling >3cm more than contralateral leg +1
Swelling of whole leg+1
Localised tenderness along deep venous system+1
Dilated collaterals present (NOT varicose veins)+1
Pitting oedema confined to symptomatic leg+1
An alternative diagnosis is at least as likely-2

 

Initial management of deep vein thrombosis

  • After history and examination, calculate the Wells score:
    • If <2, perform a D-dimer test – if negative, DVT is excluded. Consider alternative diagnoses.
    • If Wells score ≥2, or if the D-dimer is positive, proceed to Doppler and compression ultrasound examination of the venous system. If scanning is delayed, start precautionary anticoagulation whilst it is awaited.
  • Proximal DVT requires treatment
    • There are no trial data to inform whether below-knee DVT requires treatment, and some centres will not scan below the knee for that reason.
    • If diagnosis confirmed, bloods prior to treatment:
      • FBC
      • PT and APTT
      • U+E
      • LFT
  • Treatment with anticoagulation
    • Initial treatment with one of the following:
    • Low molecular weight heparin (enoxaparin, dalteparin, or tinzaparin at a therapeutic dose, depending on weight, given sub-cutaneously)
    • Apixaban (an oral Xa inhibitor, given at a dose of 10mg twice daily for 7 days, then 5mg twice daily thereafter. It is contraindicated if eGFR<15ml/min.)
    • Rivaroxaban (an oral Xa inhibitor, given at a dose of 15mg twice daily for 21 days with food, then 20mg once daily thereafter. It is contraindicated if eGFR<15ml/min)

 

Further management of deep vein thrombosis

Anticoagulation
  • After initial treatment, anticoagulation can continue with one of the above anticoagulants, or switch to warfarin or dabigatran.
    • Warfarin initiation requires frequent INR monitoring, and concurrent LMWH at a therapeutic dose until INR>2 for 24 hours. This is because warfarin also inhibits synthesis of proteins C and S, which have a shorter half life than other vitamin K-dependent clotting factors, and so the initial effect of warfarin is prothrombotic.
    • Dabigatran (an oral thrombin inhibitor) is given at a dose of 150mg twice daily, or 110mg twice daily if elderly, if eGFR<50ml/min or receiving concurrent verapamil. It is contraindicated if eGFR<30ml/min.
  • Duration of anticoagulation depends on previous history and whether the DVT was provoked by a transient risk factor e.g. surgery.
    • Patients with recurrent unprovoked VTE should receive long-term anticoagulation.
    • A first episode of provoked VTE requires anticoagulation for at least 3 months, and consider re-scanning for residual thrombus, in which case extend anticoagulation to 6 months.
    • Use clinical judgement to assess risk of recurrence in those with first unprovoked VTE or recurrent provoked VTE. In general, most patients do not need anticoagulation beyond 6 months but some will be at high risk of recurrence.
Other options
Investigation for underlying causes
  • Most risk factors will become apparent in the history, examination and initial testing.
  • Consider investigation for underlying malignancy in those over 55yrs with first unprovoked DVT
  • Testing for inherited thrombophilias is generally not recommended, as it does not alter management. Furthermore acute thrombus and anticoagulant drugs affect levels of clotting factors so tests are not interpretable.
  • In those with recurrent unprovoked DVT or thrombosis in unusual sites (e.g. arm, cerebral sinuses, splanchnic veins)  consider testing for antiphospholipid syndrome (Lupus anticoagulant, anti-cardiolipin and anti-β2 glycoprotein 1), myeloproliferative neoplasms (for JAK2 mutations) and paroxysmal nocturnal haemoglobinuria (by flow cytometry).

 

Complications of deep vein thrombosis

  • The major complication is pulmonary embolism, which may be fatal. This is why treatment is needed even if there are no symptoms, urgently.
  • A post-thrombotic syndrome is described, including chronic pain, oedema, haemosiderin deposition and varicose veins can develop. Compression stockings are ineffective in preventing it.
  • Thrombus can be a nidus for infection, particularly in intravenous drug users, in whom chronic endovascular infection may initially present as occult fever.

 

Prognosis of deep vein thrombosis

  • Isolated DVT generally has a good prognosis, with rates of post-thrombotic syndrome of 5-15% depending on the definition used.
  • Recurrent rates depend on the severity of ongoing risk factors.

 

Now click here for exam questions about DVT

Common exam questions and answers for doctors and medical students

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Questions about DVT (Deep Vein Thrombosis)

DVT (Deep Vein Thrombosis) Questions

Common DVT exam questions and answers for doctors, medical students and exams

 

What is the definition of a proximal DVT?

  • A thrombus in the popliteal, superficial femoral, deep femoral, common femoral or external iliac vein.

What is Virchow's Triad?

  • Blood stasis, procoagulant tendency, and endothelial injury. Each of these can lead to thrombosis.

Give 4 transient risk factors for DVT?

  • Immobilisation
  • Surgery
  • Trauma
  • Acute infectious or inflammatory illness

What is the Wells score?

The Wells score quantifies the pre-test probability of DVT and guides further investigation:

Active cancer+1
Recently bedridden ≥3 days or major surgery in the past 12 weeks+1
Paralysis, paresis or recent plaster immobilization of affected leg+1
Previously documented DVT+1
Calf swelling >3cm more than contralateral leg +1
Swelling of whole leg+1
Localised tenderness along deep venous system+1
Dilated collaterals present (NOT varicose veins)+1
Pitting oedema confined to symptomatic leg+1
An alternative diagnosis is at least as likely-2

How does the Wells score guide further investigation?

  • If <2, perform a D-dimer test – if negative, DVT is excluded. Consider alternative diagnoses.
  • If ≥2, or if the D-dimer is positive, proceed to Doppler and compression ultrasound examination of the venous system.

Is treatment indicated for a below-knee DVT?

  • It is not known whether a below-knee DVT confers increased risk of PE; it is certainly a common incidental finding in otherwise well individuals.
  • If local symptoms are thought to be due to the DVT, offer treatment. If not, consider repeat scanning in one week to see if the clot has extended proximally.

Which patients with DVT should undergo investigation for an underlying cause?

  • Those aged >55yrs with unprovoked DVT, and those with recurrent unprovoked DVT or DVT at an unusual site.

 

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Anaemia – Exam questions and answers

Questions about anaemia

Common anaemia exam questions for doctors and medical students 

 

How can causes of haemolysis be classified?

  • Congenital or acquired
  • Immune-mediated or non-immune mediated
  • Intravascular or extravascular

What are the common causes of a microcytic anaemia?

  • Overwhelmingly the most common is iron-deficiency
  • Thalassaemia
  • Sideroblastic anaemia
  • Lead poisoning

What are the common causes of a macrocytic anaemia?

  • B12 or folate deficiency
  • Myelodysplastic syndrome
  • Brisk bleeding or haemolysis
  • Hypothyroidism and alcohol cause macrocytosis, but not typically anaemia

What are the common causes of normocytic anaemia?

  • Renal failure
  • Chronic inflammation
  • Bone marrow failure

What proportion of the healthy population have a positive DAT?

  • Approximately 5%, so a positive DAT is not evidence of haemolytic anaemia, in the absence of other findings such as a raised bilirubin, LDH and reticulocyte count.

 

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