# Aetiology

Aetiology

The three factors described by Virchow over a century ago are still relevant in the development of  venous thrombosis. These are: /uni25CF contact of  blood with an abnormal surface (e.g. endothelial damage); /uni25CF abnormal flow (e.g. stasis); /uni25CF abnormal blood (e.g. thrombophilia). - There are many predisposing causes for VTE. These are listed in Table 62.2 . The most important factor is a hospital admission for treatment of  a medical or surgical condition. Injury , especially fractures of  the lower limb and pelvis, pregnancy and the oral contraceptive pill are other well - recognised predisposing factors. Endothelial damage is now known to be critically important. The interaction of  the endothelium with inflammatory cells, or previous deep vein damage, renders the endothelial surface hypercoagulable and less fibrinolytic. Stasis is a predisposing factor seen in man y of  the conditions described in Table 62.2 , especially in the postoperative period, in patients with heart failure and in those with arterial ischaemia. - ) and 

(a)
diagnostic venogram;
(b)
therapeutic
Figure 62.30
Post-thrombotic leg demonstrating features of eczema,
pigmentation and mild lipodermatosclerosis.

/uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF A number of  conditions are associated with increased coagulability of  the blood (thrombophilia) ( Table 62.3 Deficiencies of  antithrombin, activated protein C and protein S have all been shown to predispose to venous thrombosis in young patients. Activated protein C deficiency is associated with inheritance of  the factor V Leiden gene and may account for the higher incidence of  venous thrombosis in white populations (being present in 6–7%). It results in a small increase in the risk of  VTE, although it may act in concert with some of  the other predisposing factors. A thrombophilia should be excluded in any patient presenting with an episode of  VTE who gives a family history of  VTE or in whom there is no other predisposing factor. Although the development of  DVT is probably multifac torial, immobility (and hence stasis) remains one of  the most important factors. DVT is recognised as a complication of long-haul flights and other forms of  travel. 

Patient factors
Age
Obesity
Varicose veins
Immobility
Pregnancy
Puerperium
High-dose oestrogen therapy
Previous deep vein thrombosis or pulmonary embolism
Thrombophilia (see
Table 62.3
)
Disease or surgical procedure
Trauma or surgery, especially of pelvis, hip and lower limb
Malignancy, especially pelvic, and abdominal metastatic
Heart failure
Recent myocardial infarction
Paralysis of lower limb(s)
Infection
In
/f_l
ammatory bowel disease
Nephrotic syndrome
Polycythaemia
Paraproteinaemia
Paroxysmal nocturnal haemoglobinuria antibody or lupus
anticoagulant
Behçet’s disease
Homocystinaemia