Vasculitis is a condition characterized by inflammation within the walls of blood vessels, affecting arteries, veins, and capillaries throughout the body. This inflammation causes vessel walls to thicken, narrow, and potentially scar, restricting blood flow and damaging tissues and organs. Because the skin is highly vascularized, the lower legs are a frequent and visible site for these disease manifestations.
What Causes Blood Vessel Inflammation
Vasculitis is defined by inflammation largely due to a misguided immune system response that attacks the healthy components of the blood vessel wall. This attack involves the migration of white blood cells into the vessel tissue, causing damage and necrosis. The resulting injury causes the vessel to leak blood and fluid into the surrounding tissue, which is responsible for the visible skin changes.
Vasculitis can be broadly categorized as either primary or secondary, depending on the underlying cause. Primary vasculitis, such as IgA vasculitis, occurs without any known trigger and is often a diagnosis of exclusion. Secondary vasculitis is triggered by another health issue, such as a reaction to a medication, a viral or bacterial infection, or an underlying autoimmune disorder like lupus or rheumatoid arthritis. In many cases, no specific cause is ever identified.
How Vasculitis Appears on the Legs
The visual presentation of vasculitis on the legs is highly varied and depends on the size and depth of the blood vessels affected. The legs are commonly involved because of gravity and the pressure exerted on vessels in dependent areas. Skin manifestations may be the only sign of the condition, or they may indicate systemic involvement.
A common and distinct sign is palpable purpura, which appears as raised red, purple, or brown spots felt on the skin surface. These spots do not blanch when pressed because they are caused by red blood cells leaking out of damaged small vessels. The swelling of the vessel wall and surrounding inflammation makes the lesions palpable.
The inflammation can also present as persistent urticaria, a hive-like rash that remains in the same location for longer periods than common hives. When medium-sized vessels deeper in the skin are involved, more severe changes can occur, including the formation of nodules and ulcers. Nodules are painful, firm lumps beneath the surface, while ulcers are open sores resulting from tissue death due to lack of blood flow.
Another pattern signaling deeper vessel involvement is livedo reticularis, a mottled, net-like, reddish-blue discoloration of the skin. This web-like pattern is caused by disrupted blood flow in the capillaries and venules, often appearing on the thighs and lower legs. Skin changes can range in size from tiny petechiae to larger patches that coalesce, sometimes involving blistering or crusted lesions.
Accompanying Physical Symptoms
The skin rash is often accompanied by other physical symptoms indicating the inflammatory process is affecting the body beyond the skin. A general feeling of being unwell, unexplained weight loss, and fatigue are common complaints.
Musculoskeletal complaints frequently occur alongside the rash, including joint pain and muscle aches. A low-grade fever that cannot be explained by an infection is also a frequent symptom of systemic vasculitis.
Locally, the skin lesions themselves can cause discomfort. Patients may report a localized burning sensation, itching, or pain around the affected patches of skin. If nerve involvement occurs, individuals might experience numbness or tingling in the hands and feet, signaling inflammation affecting the peripheral nerves.
Importance of Medical Evaluation
Observing a persistent or unusual rash on the legs, especially one accompanied by systemic symptoms, requires prompt medical evaluation. Self-diagnosis is unreliable, as vasculitis can mimic other conditions. A medical professional can differentiate vasculitis from these other skin problems, which is necessary because the underlying cause and potential for organ involvement vary widely.
The diagnostic process typically involves a physical examination and laboratory work. Blood tests look for general markers of inflammation, such as an elevated C-reactive protein or erythrocyte sedimentation rate. Specific antibody tests, like the antineutrophil cytoplasmic antibody (ANCA) test, are often used to help identify certain types of vasculitis. The most definitive diagnostic tool is a skin biopsy, where a small tissue sample is taken from an affected area and examined under a microscope for signs of vessel wall inflammation and damage. Early and accurate diagnosis is important to manage the disease and prevent potential complications, such as damage to the kidneys, lungs, or other internal organs.