Systemic vasculitis is a group of uncommon diseases defined by inflammation within the walls of blood vessels (vasculitis). This inflammation causes the blood vessel walls to thicken, narrow, or scar, which can reduce or completely block blood flow to tissues and organs. The condition is termed “systemic” because it can affect blood vessels in virtually any organ throughout the body. This widespread inflammation can lead to diverse and serious health issues.
The Underlying Cause of Systemic Vasculitis
Systemic vasculitis is primarily considered an autoimmune disorder, where the body’s immune system mistakenly attacks its own healthy tissues. The immune response targets the cells lining the blood vessels, leading to the inflammation and damage that characterizes the disease.
The precise mechanism that triggers this autoimmune response is often unknown, leading to a classification of “primary” or idiopathic vasculitis. Triggers known to precede onset in some cases include chronic infections (particularly hepatitis B and C viruses), reactions to certain medications, genetic predisposition, and environmental factors.
Categorizing Vasculitis by Vessel Size
The most widely accepted method for classifying systemic vasculitis is based on the size of the blood vessel predominantly affected by the inflammation. Established by the Chapel Hill Consensus Conference, this system organizes the diseases into large, medium, and small vessel categories. The size of the affected vessel directly influences which organs are involved and how the disease manifests.
Large Vessel Vasculitis
Large vessel vasculitis (LVV) involves the aorta, the body’s main artery, and its major branches. Inflammation in these arteries can severely restrict blood flow to large areas of the body, such as the head, neck, and limbs. Diseases in this category include Takayasu arteritis and Giant Cell Arteritis (GCA), which often affect the arteries supplying the head and neck.
Medium Vessel Vasculitis
Medium vessel vasculitis (MVV) targets the main arteries that supply blood to organs like the kidneys, intestines, and nerves. Inflammation can weaken the vessel wall, sometimes leading to the formation of small aneurysms or bulges. Polyarteritis Nodosa (PAN) is an example in this group, characterized by inflammation that spares the smallest vessels.
Small Vessel Vasculitis
Small vessel vasculitis (SVV) affects the body’s microscopic blood vessels, including arterioles, capillaries, and venules. This type often damages organs densely packed with capillaries, such as the kidneys and lungs. Granulomatosis with Polyangiitis (GPA) and Microscopic Polyangiitis (MPA) are examples that frequently involve the upper respiratory tract and kidneys.
Recognizing the Signs of Organ Involvement
The symptoms of systemic vasculitis are highly variable and depend on the location and extent of the inflamed blood vessels. Many patients first experience non-specific systemic symptoms, such as unexplained fever, fatigue, and unintended weight loss, which can make initial diagnosis challenging. These general complaints result from the body-wide inflammatory process.
When the inflammation targets the small vessels in the skin, a characteristic rash known as palpable purpura may develop, often on the lower limbs. This rash appears as raised, non-blanching red or purple spots. Involvement of the blood vessels supplying the joints and muscles can cause pain and stiffness, or a condition called myalgia. If the inflammation affects the blood supply to the peripheral nerves, patients may develop numbness, tingling, or weakness in the extremities.
Vasculitis can also affect internal organs, particularly the kidneys and lungs. Kidney involvement may lead to blood or protein in the urine, and if severe, can rapidly progress to kidney failure. Inflammation in the lungs can cause coughing, shortness of breath, and sometimes even life-threatening bleeding into the air sacs. The diverse nature of these symptoms across different organ systems highlights why the disease is termed systemic.
Diagnosis and Management Strategies
The diagnosis of systemic vasculitis requires a comprehensive approach because of its varied and non-specific presentation. The initial evaluation involves a detailed clinical history, physical examination, and laboratory tests to measure inflammatory markers, such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). Specialized blood tests are also conducted to look for autoantibodies, particularly the anti-neutrophil cytoplasmic antibodies (ANCA), which are characteristic of certain small vessel vasculitides.
Imaging techniques, like angiography, computed tomography (CT) scans, or magnetic resonance imaging (MRI), are used to visualize the affected blood vessels, especially in large and medium vessel types. The definitive diagnosis, however, often relies on obtaining a tissue biopsy from an affected organ, such as the skin, kidney, or nerve. This tissue sample allows a pathologist to microscopically confirm the presence of inflammation and destruction within the vessel wall.
The primary goal of management is to quickly control the inflammation and suppress the overactive immune system to protect organs from irreversible damage. Treatment typically involves a two-phase approach: induction to achieve remission, followed by maintenance to prevent relapse. High-dose corticosteroids, such as prednisone, are frequently used to rapidly reduce inflammation.
These are usually combined with more potent immunosuppressive agents, such as cyclophosphamide or rituximab, particularly for severe or organ-threatening disease. Once the disease is under control, less toxic drugs like azathioprine or methotrexate are used for long-term maintenance therapy. Regular monitoring is then necessary to assess disease activity and adjust treatment protocols to minimize potential side effects from the powerful medications.