Vasculitis is sorted by vessel size, from the aorta to the tiniest capillaries
Vasculitis is not one disease but a family of conditions in which inflammation attacks and damages blood vessels, arteries and veins alike. Doctors classify them largely by how big the affected vessels are, and that size goes a long way towards deciding which symptoms appear in the skin and organs.
The damage is driven mainly by white blood cells migrating into vessel walls. Early complaints tend to be vague: fever, headache, tiredness, aching muscles and joints, and weight loss. Any form, even one centred on the largest arteries, can show on the skin, most often as purpura, nodules, a lace-like mottling called livedo reticularis, ulcers or hive-like purple patches.
The standard naming scheme comes from the 2012 Chapel Hill Consensus Conference, which first splits cases into primary systemic, secondary and single-organ types. Primary systemic disease is then grouped by vessel size. Large-vessel vasculitis tends to strike the aorta and its main branches, with Takayasu arteritis and giant cell arteritis the two chief forms. Medium-vessel disease targets the arteries feeding the internal organs, as in polyarteritis nodosa and Kawasaki disease. Small-vessel disease divides into a group tied to antineutrophil cytoplasmic antibodies, known as ANCA, with few immune deposits, and an immune complex group with heavy antibody and complement deposits, which includes IgA vasculitis, also called Henoch–Schönlein. A variable-vessel category, covering Behcet's disease and Cogan's syndrome, can hit vessels of any size or type.
Autoimmune causes are the most common. Secondary vasculitis is thought to be set off by something else, such as rheumatoid arthritis, cancer, a drug or an infection; notable infectious triggers include tuberculosis, HIV, infective endocarditis and hepatitis B and C. Apart from rheumatoid vasculitis, most secondary forms are extremely rare. Single-organ vasculitis stays confined to one organ or system, for instance the skin, the gut or the peripheral nerves.
Blood tests in active disease usually point to inflammation, with a raised sedimentation rate and C-reactive protein, anaemia and more white cells; ANCA levels or blood in the urine may also show up. A firm diagnosis, though, rests on a biopsy of affected tissue, such as skin, lung, nerve or kidney, which reveals the pattern of inflammation in the vessels.
Source: Vasculitis
