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