What is the cause of leg ulcers?
Venous leg ulcer with macerated skin due to dressings
There are several different causes of leg ulcers:
venous causes (commonest)
arterial causes (uncommon)
other causes (rarer)
The commonest cause of leg ulcers is venous disease, and so these are called “venous leg ulcers”. The next most common cause is poor arterial circulation due to blocked or severely narrowed arteries (“arterial leg ulcers”). Due to the age that ulcers affect people, there is often a mixture of venous and arterial causes for a leg ulcer, and doctors treating leg ulcers have to determine whether the venous or arterial problems are dominant.
Other rarer causes of leg ulceration include tumours, infection, and autoimmune diseases such as vasculitis etc. Diabetes is often quoted as a cause of leg ulcers but this can cause leg ulcers in several different ways. Diabetes can be associated with smoking blocking the minute blood vessels the keep the skin alive and by affecting the sensory nerves making damage to the lower legs more likely.
What is the cause of venous leg ulcers?
As above, the commonest cause of leg ulcers is venous disease. This can be split into superficial venous reflux disease (“hidden varicose veins“) or venous occlusive disease due to previous deep vein thrombosis (“post phlebitic limb”).
Fortunately, of these two causes, the superficial venous reflux disease (“hidden varicose veins“) is much more common than the venous occlusive disease. This is fortunate because the majority of cases, superficial venous reflux can be identified by duplex ultrasound and can be successfully treated.
The mechanism of how superficial venous reflux disease (“hidden varicose veins“) causes leg ulcers will be described here in very simple terms but is explained fully in The College of Phlebology’ textbook “Understanding Venous Reflux – the Cause of Varicose Veins and Venous Leg Ulcers“.
When veins in the legs lose their valves, they become “incompetent” and blood can flow wrong way down them – called “venous reflux”. In some veins this is due to gravity alone when the person stands up (passive venous reflux), and in others it is due to blood being pumped at high pressure to the heart but leaking through incompetent veins attached to the deep venous system (active venous reflux). Whichever the cause, the abnormal flow of venous blood the wrong way down the vein causes inflammation in the skin and tissue around the capillaries drained by the affected vein.
When it starts, this inflammation is mild and has minimal effect. However, if the reflux is allowed to continue, over the months and years the chronic inflammation causes a series of problems in the skin and tissue of the leg:
• swelling due to fluid (oedema)
• itching of the skin (venous eczema)
• red stains of the skin
• brown stains of the skin
• hardness of the skin (lipodermatosclerosis or LDS)
• and eventually breakdown of the skin (leg ulcer)
If at any time during this progression the venous reflux is identified and stopped (i.e. successfully treated) then the process will reverse and the skin and tissue will start to heal.
It is the aim of a venous specialist in a specialist vein clinic to be able to identify which leg ulcers are venous, and which ones are due to superficial venous reflux (“hidden varicose veins“) and then to treat them successfully with a high chance of curing the leg ulcer permanently.
Leg ulcers due to venous occlusive disease (“post phlebitic limb”) are much more difficult to treat.
In the majority of cases, the occlusions are due to deep vein thrombosis (DVT), or something pressing on the side of the vein, compressing it and causing the blood to clot – a deep venous thrombosis (DVT) due to external compression.
If the deep vein thrombosis (DVT) is cleared away quickly, then in the majority of cases the deep veins continue to function well and the patient does not get either a leg ulcer or a “post phlebitic limb”. The “post phlebitic limb” or leg ulcer found in these cases is due to either a deep vein thrombosis (DVT) that has been allowed to remain for a long time, scarring and damage to the inside of the veins with destruction of the valves of the deep veins, or recurrent deep vein thrombosis (DVTs) which has the same effect.
In the past it has always been thought that the reflux of blood down the damaged deep vein, with the consequent impact of the blood in the tissues of the ankle and the resulting inflammation, causes damage to the skin and fat of the lower leg over the years, resulting in the discolouration, swelling, hardness tissue and eventual ulceration.
Over recent years, some specialist units have had success in opening up the drainage of the deep veins by removing the deep vein thrombosis (DVT) or compression on the vein itself, with clinical improvement in the leg and often healing of the leg ulcer. Therefore in leg ulcers that are due to deep vein occlusive disease, it does seem to be a combination of the incompetent valves of the deep veins allowing deep vein reflux of blood as well as a problem of poor drainage due to partial or blockages in the deep veins.