Vasculitis is a condition characterized by inflammation of the body’s blood vessels, which include arteries, veins, and capillaries. When vasculitis occurs, the inflamed vessel walls can thicken, narrow, or weaken, potentially disrupting blood flow. This disruption can lead to a range of complications depending on which parts of the body are affected.
The Body’s Attack on Blood Vessels
Vasculitis primarily involves a mistaken attack by the immune system on the blood vessels. Normally, the immune system defends the body against foreign invaders. In vasculitis, however, this protective system erroneously targets the cells within the blood vessel walls, perceiving them as harmful. This leads to an inflammatory response where immune cells infiltrate and damage the vessel lining.
The inflammation causes blood vessel walls to swell and thicken, reducing the space for blood flow. This narrowing, known as stenosis, restricts oxygen and nutrient delivery to affected tissues and organs. Inflammation can also weaken vessel walls, causing them to bulge outwards, forming an aneurysm. If an aneurysm ruptures, it can lead to dangerous internal bleeding.
Compromised blood vessels may also become sites for blood clot formation. These clots can further obstruct blood flow, potentially leading to tissue damage or death in areas downstream from the blockage. The precise mechanisms by which the immune system initiates this attack vary among different types of vasculitis.
The resulting lack of adequate blood supply, or ischemia, can impair organ function, such as in the kidneys, lungs, or brain. Over time, persistent inflammation and reduced blood flow can lead to scarring and irreversible damage within affected vessels and the tissues they supply. Understanding this immune-mediated process is central to how vasculitis develops and progresses.
Factors That Contribute
Several factors can influence vasculitis development by triggering the immune system’s abnormal response. Infections are recognized contributors, with viruses like hepatitis B and C being particularly notable. Hepatitis B, for example, can be associated with polyarteritis nodosa, while hepatitis C is linked to cryoglobulinemic vasculitis. Other infections, including certain bacteria and herpesviruses, can also provoke vascular damage.
Certain medications can also trigger vasculitis, known as drug-induced vasculitis. Examples include the antibiotic minocycline (used for acne), propylthiouracil (for hyperthyroidism), hydralazine, allopurinol, and some tumor necrosis factor (TNF) inhibitors. In these cases, the immune response to the drug can mistakenly target blood vessels, often resolving once the medication is stopped.
Underlying autoimmune diseases significantly increase susceptibility to vasculitis. Conditions like systemic lupus erythematosus (lupus) and rheumatoid arthritis are frequently associated with secondary vasculitis. In lupus, the immune system’s overactivity can extend to blood vessels, causing inflammation. Similarly, in rheumatoid arthritis, the chronic inflammatory state can lead to blood vessel involvement, often affecting small and medium-sized vessels.
Genetic predispositions also play a role, although vasculitis is not typically inherited in a simple Mendelian fashion. Instead, a complex interplay of multiple genes, often related to immune system regulation, can increase an individual’s risk. Specific genetic variations, such as certain HLA (Human Leukocyte Antigen) genes, have been associated with a higher likelihood of developing particular forms of vasculitis, including Behçet’s disease and giant cell arteritis. This suggests that while genes do not directly cause the condition, they can make an individual more susceptible when exposed to other environmental triggers.
Different Manifestations
Vasculitis is a diverse group of conditions, each with distinct characteristics and manifestations. This diversity stems from which specific blood vessels are affected and the underlying factors contributing to inflammation. Classification often depends on the size of the blood vessels primarily involved: large, medium, or small. This categorization helps explain the varied symptoms and organ involvement seen across different types.
Large vessel vasculitis affects major arteries such as the aorta and its main branches. Examples include Giant Cell Arteritis, which typically impacts adults over 50 and affects arteries in the head and neck, and Takayasu Arteritis, more common in younger women, which can reduce blood flow to the limbs and organs. Symptoms often relate to reduced blood supply to the areas these large vessels serve.
Medium vessel vasculitis targets arteries supplying blood to organs like the kidneys, heart, and intestines. Polyarteritis Nodosa (PAN) can affect various organs and has been linked to hepatitis B infection in some cases. Kawasaki disease, another medium vessel vasculitis, primarily affects children under five and can impact the coronary arteries. Manifestations are often localized to specific organ systems.
Small vessel vasculitis involves the tiniest blood vessels, including arterioles, capillaries, and venules, often affecting the skin, kidneys, and lungs. Types like Anti-Neutrophil Cytoplasmic Antibody (ANCA)-associated vasculitis, which includes Granulomatosis with Polyangiitis, are characterized by specific antibodies that mistakenly attack immune cells, leading to vessel damage. These forms can present with rashes, kidney dysfunction, or lung issues.
Some forms of vasculitis, like Behçet’s disease, are categorized as variable vessel vasculitis because they can affect blood vessels of any size. The specific type of vasculitis, driven by its distinct mechanisms and vessel size, determines how the condition presents. Symptoms can range from skin lesions to organ failure, highlighting the complex nature of vasculitis.