17 Feb Deep Vein Thrombosis
You see a 35yo F who presents with unilateral leg swelling over the previous 36hrs. She is a fit, healthy active woman with no previous medical history and no previous history of blood clots. She takes oral hormonal contraception. She thinks she might have pulled a muscle whilst out running a couple of days ago.
There are a number of differentials to consider in this case, but deep vein thrombosis (DVT), a subtype of venous thromboembolism (VTE) ought to be high on the list of things to rule out, since there is a reasonably significant risk of serious complications, namely pulmonary embolism (PE).
Ill be looking at PE next week so keep your eyes peeled.
VTE occur most commonly in the deep veins of the leg, long saphenous and femoral veins being most frequently affected. PE takes second place with axillary vein embolism being far less common, but still worthy of consideration.
What causes VTE?
The list of risk factors is fairly extensive, but VTEs broadly fall into two categories. Provoked (usually a temporary or modifiable risk) or unprovoked (a risk that is persistent, unmodifiable or very difficult to modify).
When to suspect?
This depends on the VTE in question, but the diagnosis is largely clinical. That is based on signs and symptoms. In the grand scheme of things, the investigations aren’t overly specific other than doppler scan of the affected limb.
Let’s look at lower leg DVT for no other reason than they’re most common. They usually occur some where along the long saphenous vein, and there is typically a gradual onset (over hours/ couple of days) of diffuse unilateral lower leg swelling, inflammation, pain with distention of the distal veins (imagine putting a venous tourniquet round your arm and watching the veins fill. DVT is the same principle).
Femoral vein embolisms are less obvious but a unilateral swollen leg (whole length) with/ out venous distention would prompt your suspicion of this. Similarly with axillary vein embolism, the arm may be uncomfortable or painful, oedematous, +/- inflammation, distal veins of the arm/ hand are likely to be engorged.
Once we’ve got our clinical picture, history and some differential diagnoses, we start to consider the way forward. There will be those DVT’s that are obvious, but a significant proportion will not be ‘text book’.
2- Level Wells Score is the mainstay of risk stratification for DVT. It is far simpler and less subjective than the original Wells Score, identifiying DVT as either likely or unlikely. Simples.
If used correctly you can expect it to miss <25% (sensitivity 77-98%), but it performs less well as an exclusion tool. Specificity is poor at 38-58% (i.e 2 Level wells score will exclude DVT in <58% of patients who don’t have a DVT). So it doesn’t perform well enough to be the only diagnostic tool.
D-Dimeris probably the most useful blood test in the diagnosis of VTE, but again it isn’t perfect, in fact far from it.
The problem with D-Dimer is that it is a very good negative predictor of VTE (i.e it is a reliable way of excluding VTE in low risk patients), but it is ineffective as a positive predictor (i.e you can’t diagnose VTE based on D-Dimer). D-Dimer can be elevated during infection, following surgery or substantial injury (e.g leg fracture, large muscle rupture, burns), in pregnancy and in cancer or thrombophilia.
For example if your patient is ‘likely’ to have a DVT (based on 2-level wells score) and they have a positive D-Dimer, then we manage them as a DVT. If they have a ‘likely’ DVT but D-Dimer is negative, that is far more reliable than a positive result, and we have probably excluded DVT, UNLESS high risk patient, in which case we manage as a DVT anyway.
Alongside D-Dimer, full blood count, liver blood tests, coagulation panel (PT, APTT, FIB) will all help to understand the underlying clinical picture, especially in those with unprovoked VTE.
The gold standard diagnostic test to confirm of exclude a DVT is with proximal leg vein ultrasound scan within 4hrs. I can confidently say that this is probably an ideal, and that realistically most centres will be able to achieve this within 24hrs. What this means is that upon diagnosis or likely diagnosis and prior to a scan, the patient is very likely to be treated with an anti-coagulant in the interim period.
If you see an elevated D-Dimer, have excluded VTE with leg scan, they need further investigation.
Whilst it is off topic slightly, we really hadn’t ought to be using D-Dimer in the community to exclude PE. If you are suspicious enough of PE to be requesting a D-Dimer, the patient needs admitting to hospital for them to exclude it.
This will depend on the services that are available locally, timing, day of the week, weather and Jupiters orbital position will all influence how, when and where your DVT patient is managed so check your local DVT pathway.
The ideal situation would be to chose an interim anti coagulant that can be continued if DVT is confirmed, but often sub cutaneous low molecular weight heparin (s/c LMWH) will be used first line during the first few days until they are seen by the coagulation clinic.
If the patient is confirmed to have a DVT, the choice of anti coagulant will most likely be decided by a specialist in secondary care with appropriate monitoring depending on the drug used.
Unprovoked DVT requires follow up and investigation to exclude thrombophilia and cancer. NICE recommend a careful review of medical history, baseline bloods and a physical examination (in those without a known active cancer). Women of child bearing age would have a pregnancy test performed (since pregnancy might be the reason they developed a clot).
I hope you’ve enjoyed the whistle stop tour of DVT. Next well we will examine PE in more detail, with a community practice focus.