Pathophysiology, clinical features and diagnosis of vascular disease affecting the limbs

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Pathophysiology, clinical features and diagnosis of vascular disease affecting the limbs

Introduction

The term ‘peripheral arterial disease’ (PAD) is often employed to mean obstructive (‘obliterative’) disease of major lower limb arteries causing ischaemia. However, a range of vascular disorders can cause symptoms in upper and lower limbs, and a broader term ‘peripheral vascular disease’ (PVD) includes any disease of arteries, veins or lymphatics outside the heart. This chapter concentrates on lower limb vascular-related problems as they are much more common; upper limb symptoms are outlined in Table 40.5 (p. 488).

Patients with PAD of the legs may have no symptoms, either because they do not walk far enough to claudicate or because the collateral circulation has developed to deliver enough blood to leg muscles. Patients with vascular limb disorders may present to any medical specialty and some require urgent action, e.g. acute limb ischaemia or a painful abdominal aneurysm. Thus all clinicians need to understand the principles of diagnosis and the scope and timing of treatment. This chapter covers the pathophysiology of limb vascular insufficiency, plus the details of history taking and examining patients with suspected vascular disease and the process of reaching a broad, ‘first stage’ diagnosis.

Vascular insufficiency of the limb (Table 40.1)

Arterial insufficiency and venous insufficiency do not indicate any specific pathophysiology and either may be acute or chronic. Limbs vascular disorders are caused mainly by atherosclerosis, arterial thromboembolism, aneurysms, complications of diabetes, and thrombotic and varicose disorders of the venous system. Sometimes several causes interact.

Acute arterial insufficiency means inadequate arterial blood supply to a limb over hours or days. It may be caused by embolism into a normal artery, in which thrombus originating in the heart or other proximal site detaches and is swept distally until it lodges and obstructs the vessel. It can also occur by in situ thrombosis of an atherosclerotic plaque in lower limb arteries, by thrombosis of a popliteal aneurysm or by an aortic dissection extending into the lower limb vessels. Any disorder can manifest in several ways—see Table 40.2 for the various manifestations of popliteal aneurysm.

Chronic venous insufficiency means inadequate venous drainage for at least 2 weeks and often much longer.

Symptoms and signs in the limb

An accurate initial diagnosis depends almost entirely on skilled and methodical clinical evaluation rather than on special investigations. Preliminary assessment notes obvious major risk factors (Table 40.3). Detailed history taking is covered in Table 40.4 and examination in Figure 40.1. In a suspected vascular case, the student or doctor tries to decide if the problem is arterial, venous or lymphatic, or has some other cause.

The principal symptoms and signs of vascular disease are pain, changes in skin texture, colour and temperature, tissue loss including ulceration, and swelling. The upper limb is affected by a largely different range of disorders with signs and symptoms with only a small overlap (see Table 40.5).

Pain

Most limb pain is due to musculoskeletal disorders such as arthritis or trauma rather than vascular disease. Where lower limb peripheral ischaemia is the working diagnosis, a full cardiovascular workup is needed (see Table 40.4 and Fig. 40.1).

Intermittent claudication

Chronic lower limb arterial insufficiency usually presents as muscular pain on walking. The history is characteristic: pain begins at a reproducible distance, is worse walking uphill and increases if walking continues; the patient usually begins to limp, accounting for the name ‘intermittent claudication’ (Latin: claudicare to limp), and the patient is forced to stop. Symptoms usually predominate in one limb. The pain subsides within a minute or two of stopping and recurs at the same walking distance. Pain is almost always in the calf, whatever level the arterial obstruction, but may extend into thigh or even buttock in aorto-iliac obstruction. If associated with impotence, this is known as Leriche syndrome.

After a thorough history, only cauda equina claudication or pseudo claudication might be mistaken for ‘true’ claudication. This is caused by compression of the cauda equina in the spinal canal by central disc protrusion or canal stenosis. Lower limb pain is also brought on by exercise but there are important differences—see Table 40.6.

Chronic ischaemic rest pain

With severe arterial obstruction, ischaemic pain occurs when the patient is in bed or even when sitting. Termed rest pain, this is usually felt in the skin of the foot and is very severe and burning. It occurs mostly at night because gravity assistance to arterial supply is lost, cardiac output falls at rest, and skin vessels dilate with warmth. The pain is characteristically relieved by hanging the leg out of bed or even walking around and is not fully relieved by any analgesics. Often, patients end up sleeping in a chair, causing lower limb oedema. Patients often present after tolerating this severe pain for several weeks. Only 10% of claudicants progress to rest pain.

There may also be skin changes or tissue loss such as gangrene and ulceration (see below). The term critical ischaemia implies that loss of part of the limb is inevitable unless it is revascularised. Beware of the trap in diabetic patients with neuropathy—severe ischaemia may be painless. Disruption of small vessel autonomic control may mean a severely ischaemic foot is warm and red rather than cold and white or blue. In the absence of palpable pulses, only arteriography will reveal the truth.