Varicose veins are a common symptom or sign of chronic venous disease. They are a cause of considerable morbidity, both in terms of physical symptoms and cosmesis, and have significant financial implications for health service resources. A proportion of varicose veins are due to the pathology of the long saphenous vein which has become refluxing and dilated. This may lead to discomfort and swelling in the gaiter area and even progression to venous leg ulceration. In order to understand what causes varicose veins, it is necessary to have a clear understanding of the normal structure and function of the vein.
Overview of Varicose Veins
For others, varicose veins are a means to an end to a much more serious issue. In normal healthy veins, blood is circulated to the heart through a system of one-way valves. These valves prevent the backflow of blood. When the valves fail, blood can flow in a retrograde manner and can even become pooled in the vein. This valve failure is known as venous reflux and is the cause of varicose vein. CVD often begins as varicose veins and can later progress to more serious issues such as edema, skin changes, and leg ulcers. These are caused by the increased pressure and chronic nature of venous hypertension as a result of the increased pooling in the veins.
What exactly are varicose veins? This question is not as simple to answer as one may think. The most basic explanation is that varicose veins are enlarged veins near the surface of the skin. However, those suffering from varicose vein disorders or the more serious chronic venous disease (CVD) states have a much more prolonged and complicated experience. For some, varicose veins are simply a cosmetic issue. This can be unsightly for those who suffer from it, but varicose veins are much more than cosmetic. In truth, the cosmetic issue of varicose veins is often the least damaging to the patient, but the one which medicine has the most effective treatment. Primarily, treatments such as sclerotherapy and endovenous ablation are minimally invasive and effectively eradicate unsightly veins. These treatments are often performed by phlebologists or vascular surgeons. Unfortunately, however, the underlying cause of the varicose veins is often not addressed by such treatments and the patient is merely returned to square one with a recurrence of the same issue or the development of new varicosities.
Importance of Understanding Disease Progression
Finally, a disease-specific health-related quality of life tool can be developed which will allow accurate assessment of disease impact and treatment effectiveness in comparison to other diseases.
This approach has been used in chronic venous disease with the development in the last decade of the C-classification based around clinical, etiological, anatomical and pathophysiological (CEAP). This classification is based on studies of disease progression, attempting to correlate different clinical findings with the underlying pathophysiology and anatomy of the disease. The ability to predict the progression of a disease process will also enable the identification of patients at risk of developing complications of the disease, allowing early intervention to prevent such complications. This is particularly relevant to venous disease with chronic venous ulceration being a major cause of morbidity and cost to health services.
Understanding disease progression is important in order to improve treatment and to predict outcomes of a disease process. This is particularly important in the management of a chronic disease such as varicose veins, where there are a number of different treatment options available, which are all aimed at different points in the disease process. Knowledge of the natural history of a disease and the likely impact of treatment upon it is essential for the accurate selection of patients for a particular treatment and in the assessment of the effectiveness of the treatment employed.
Inflammation and Varicose Veins
This research project aimed to investigate the changes of inflammatory cell markers and mediators using immunohistochemical and Western blotting analysis, which has not been fully determined in the pathogenesis of varicose veins. The findings produced showed the presence of chronic inflammation, suggesting that the changes of the venous wall in varicose veins were the result of a sustained cellular and molecular inflammatory process. This was confirmed by the increased levels of inflammatory cell markers and mediators in varicose veins compared to normal veins, and the greater grade of varicose veins showing increased expression of these agents. An understanding of the inflammatory phase of varicose veins is of great importance, as it may be possible to prevent progression of the disease in early varicosity by the suppression of inflammation. This may open new therapy for varicose veins, which is currently confined to treatment by surgery or support stockings.
Small saphenous and great saphenous veins from patients with primary varicose veins were examined with a fully quantitative grading system to compare levels of inflammatory cell infiltration, using immunohistochemistry for leukocyte (CD45), T-cell (CD45RO), macrophage (CD68), neutrophil (neutrophil elastase) and mast cell (tryptase) markers. Levels of adhesion molecules (intracellular adhesion molecule-1 and vascular cell adhesion molecule-1) and chemokine-regulated proteins (macrophage-inflammatory protein-1 and interferon-γ-inducible protein-10) were assessed to identify inflammatory mediators, and the changes of smooth muscle cells to myofibroblast-like cells were also studied. There were increased levels of all inflammatory cell types in varicose veins, which were particularly prominent in areas with marked endothelial damage, at which cells of the blood stream appeared to have infiltrated into the intima and media layers. There was a significant decrease of mast cell levels with transfer of technical grade to the clinical grade of varicose veins, reflecting that degradation of the extracellular matrix was a late change in the pathogenesis of varicose veins. Adhesion molecules and chemokines were particularly expressed around the inflammatory cells at sites of venous damage, and the induction of these proteins was likely to be responsible for the inflammatory cell infiltration. Smooth muscle cells were markedly increased in the intima and media of varicose veins, with most cells showing changes to myofibroblast-like cells.
Role of Inflammation in Vein Wall Damage
The vein wall forms a barrier between the blood and surrounding tissue, providing a conduit for venous return to the heart. Changes in the vein wall are central to the development of chronic venous disease and its complications. Although the initiating events are unclear, various injuries to the vein wall can lead to chronic venous disease. At the level of the capillary, increased hydrostatic pressure within the vein can result in leakage of red cells into the pericapillary tissue. Failure of an incompetent valve can lead to reflux of blood into the capillary bed and microtrauma to the vessel wall. At the macroscopic level, gridiron haemorrhages and white cell trapping are seen in patients with venous ulcers. These diverse forms of vein wall injury are united by a common histopathological process, namely inflammation. In general, the acute inflammatory response to tissue injury is aimed at debris removal and site clearance, leading to regeneration of the affected tissue. However, the nature of the vein wall injury and the various proinflammatory stimuli means that inflammation becomes chronic and is itself responsible for causing further tissue damage.
Inflammatory Mediators and Cellular Responses
Cvi is strongly associated with an inflammatory effect within the microvasculature. A number of studies have demonstrated a significant increase in inflammatory cells within the microvascular wall. Immunohistochemical staining of cvi vein samples has indicated an increase in neutrophils, monocytes and activated macrophages, usually not found in the normal microvasculature. In response to venous hypertension, leukocytes are thought to adhere and extravasate into the surrounding tissue through increased expression of adhesion molecules on the endothelium surface. Activated leukocytes will release cytokines and growth factors, inducing further inflammation and vein wall damage. This perpetuating cycle of leukocyte mediated inflammation has been supported by experimental data in which an induced inflammatory response in the form of an air pouch model, caused increased vein wall fibrosis and deterioration of valve function. High expression of E selectin and VCAM-1, adhesion molecules involved in leukocyte attachment, have been found on the surface of varicose veins, with a positive correlation seen between their expression and intensity of inflammation. Despite these results, there are still a number of conflicting reports as to whether inflammation is a cause or the result of vein wall damage. The latter was suggested by Coleridge Smith, recommending that it would be logical to treat the inflammation caused by venous reflux, but this would not halt progression of the disease as inflammation is a secondary effect.
Impact of Inflammation on Blood Flow
In patients with varicose veins, symptoms and signs of inflammation are often present. Patients with deep vein thrombosis or postphlebitic syndrome have elevated levels of certain markers of inflammation in blood and in the tissue in the affected extremity. In vivo microscopy studies have documented the presence of inflammatory cells in the tissue surrounding the tibial and saphenous veins in patients with varicose veins. This implies that inflammation may extend beyond the venous segments directly affected by varicose changes. The impact of inflammation on the progression of venous disease or on the types or severity of symptoms in these patients is not clear. It is uncertain whether inflammation initiates certain varicose vein symptoms or whether an underlying biochemical abnormality in the vein wall predisposes to both inflammation and progression of disease. However, data about the impact of inflammation on vein wall or valve function are increasingly available. In one study, bioengineered human vein grafts were implanted into the arterial circulation of nude mice and allowed to develop neointimal lesions. Mitigation of inflammation and neointima formation were associated with increased graft wall thickness, decreased compliance and altered contractile behaviour of the grafted vein. The increased wall thickness was due to an increase in smooth muscle and extracellular matrix proteins. Further evidence for links between inflammation, altered vein wall composition and compromised venous function has been provided by the work of Wakefield and colleagues, who have studied the impact of experimentally induced venous hypertension in the presence and absence of acute inflammation. They found that the presence of inflammation resulted in failure of adaptive remodelling in response to increased venous pressure and worsening of downstream oedema.
Disease Progression in Varicose Veins
Vein wall remodeling and fibrosis Chronic venous hypertension causes changes in the vein wall and surrounding tissue. In early stages, there is an increase in vein wall tension and dilation in order to accommodate increased volume. However, it is thought that this dilation is counterproductive as such veins have decreased wall tension and are more compliant. Increased compliance leads to further reflux and progression of varicose veins. Prolonged dilation causes elastin fiber damage, and this is thought to be the key event causing permanent changes to the vein wall. Elastin damage is first repaired by increased production of connective tissue proteins by fibroblasts. Over time, this results in the deposition of Type I and Type III collagen and progressive fibrosis. Fibrosis increases vein wall stiffness and further promotes the formation of varicose veins. High levels of collagen in the vein wall have been directly correlated with severe chronic venous disease.
Initial valve dysfunction and venous reflux Normal venous blood flow between the legs and the heart is maintained through a system of one-way valves in the veins. When the limbs are in dependent positions and during periods of increased abdominal pressure, these valves prevent blood from flowing backwards. Venous reflux, which is the retrograde flow of blood caused by valve dysfunction, is considered the primary cause of varicose veins. Reflux occurs in the superficial venous system; when the valve at the saphenofemoral or saphenopopliteal junction becomes incompetent, blood flows down the vein and increases pressure on the more distal valves. Secondary valve incompetence develops as this elevated pressure is transmitted to the distal veins. During venous reflux, increased venous pressure causes dilation of the vein, which can affect both the caliber and function of the vein.
Initial Valve Dysfunction and Venous Reflux
Valvular incompetence and venous reflux are widely accepted as primary causes of varicose vein formation. The normal function of the venous system is to return blood to the heart efficiently and unaided. In the lower limbs, this is achieved by contraction of the calf muscle (muscle pump) and opening and closing of the venous valves. When the valve function is impaired, the column of blood is no longer supported effectively in the standing position. Prolonged increase in venous pressure transmits to the smaller veins and capillaries, resulting in dilatation and tortuosity. Clinical evidence of this is seen as telangiectasia (spider veins) and reticular veins. Increased pressure also results in leakage of fluid and macromolecules into the surrounding tissue, causing edema. This is the defining process of venous reflux and is identified as the primary pathological event in the onset and progression of CEAP classes C4b and C5 (skin damage with or without edema). Venous reflux can be identified by manual calf compression and release with duplex ultrasonography. This is done by locating the sapheno-femoral or sapheno-popliteal junction during Valsalva and identifying the reversal of blood flow along the vein of interest. The results of this study display the prevalence of refluxing veins in symptomatic and asymptomatic people.
Vein Wall Remodeling and Fibrosis
TGF-β is a potent stimulator of ECM accumulation by fibroblasts and myofibroblasts and has been shown to increase collagen synthesis and decrease collagen degradation in a number of cell types. TGF-β also stimulates fibroblast and myofibroblast differentiation from fibroblasts and smooth muscle cells, respectively. This is significant in the context of varicose veins as myofibroblasts are likely to have a more profound effect on vein wall fibrosis than fibroblasts due to their increased synthetic and contractile properties. High levels of CTGF are associated with conditions of excessive ECM production, and CTGF may potentiate TGF-β-mediated effects on fibrosis by increasing its stability and effects on collagen synthesis. A recent study by our group has demonstrated that the severity of clinical chronic venous disease is positively correlated with TGF-β levels in plasma, and TGF-β has been shown to be specific to venous disease rather than systemic inflammation. This explains the levels of TGF-β and CTGF have been shown to be higher in limbs affected by venous disease compared to control limbs. TGF-β has also been demonstrated to be upregulated by shear stress on the vein wall, and this is significant in the context of chronic venous disease as reflux results in a sustained increase in vein wall pressure and shear stress.
Remodeling and fibrosis of the vein wall in varicose veins has been shown to occur at the level of the venous segments affected by reflux. This is a continuous, progressive process that affects the vein wall structurally and biomechanically. In the early phase, leukocytes and platelets migrate into the vein wall and degranulate, releasing a number of cytokines and growth factors which have been shown to upregulate adhesion molecule expression on venous endothelial cells. This may perpetuate leukocyte migration and exacerbate the inflammatory process. This has been demonstrated by elevated levels of intercellular adhesion molecule-1 (ICAM-1) and P-selectin expressed by vein wall endothelium in limbs affected by venous disease. Upregulation of ICAM-1 enhances vein wall inflammation by increasing migration of lymphocytes into the vein wall. Platelets release transforming growth factor beta (TGF-β) and connective tissue growth factor (CTGF), both of which have profound effects on extracellular matrix (ECM) production.
Chronic Inflammation and Complications
Their importance in mediating progression to more severe forms of chronic venous disease and in the modulation of vein wall fibrosis and ulceration could provide new therapeutic targets.
Early vein wall hypoxia activates an anergic phenotype in infiltrating macrophages, inhibiting their migration and phagocytic activity. Ongoing hypoxia and the resulting cycle of red cell and iron extravasation and subsequent degradation and macrophage uptake lead to localized intra and extracellular hemosiderin accumulation and increases oxidative stress. These changes are likely to be key drivers of conversion to the fibrosis found in chronic venous disease and the development of skin changes and ulceration.
The recent development of a unique mouse model of venous hypertension has allowed a detailed study of the inflammatory processes in early venous disease. Our data indicate that the effects of vein wall hypoxia and the resulting microenvironmental changes on macrophage and leukocyte activity are likely to be of central importance in determining the nature of inflammatory responses during the initiation of venous disease.
Chronic inflammation and particularly the role of activated macrophages have been implicated as a feature of many chronic venous disease states. But progress in our understanding of the inflammatory processes in varicose veins has been slow. Macrophage and leukocyte infiltration of the vein wall is a feature of early varicose vein disease, but separating cause and effect with respect to leukocyte activation and specific aspects of vein wall remodeling in human disease has been difficult.
