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The vasculitides that affect small, medium and large vessels are pathologically different. It is thus possible that different pathogenetic mechanisms are responsible for the distinct conditions.
Vasculitides that affect medium-sized vessels include:
These conditions tend to have a predilection for vessel bifurcations. Researchers suggest that this phenomenon may be related to the expression of adhesion molecules and intimal macrophages, which are both found in increased numbers at these sites.
KD typically affects children under 12 years. Its most ominous presenting feature is coronary artery aneurysms due to inflammation of the coronary arteries. Aneurysms of the coronary vessels occur in up to a fifth of the patients.
Aneurysms have the potential to lead to myocardial infarctions (or heart attacks), heart failure, pericarditis and myocarditis, among others. Multi-system involvement can be seen. Despite the possible serious consequences, KD is usually an acute self-limiting condition. Asian children have a higher incidence, with a male preponderance. KD is also the leading cause of non-congenital heart disease in children in the USA and the United Kingdom.
The typical clinical presentation includes:
Criteria needed to establish a diagnosis according to the North American recommendations include the presence of a fever with four out of any of the other five remaining clinical manifestations listed above.
The prognosis of KD is generally good. Treatment includes aspirin and intravenous immunoglobulin, administered within 10 days of onset. These drugs have been shown to reduce the occurrence of aneurysms and thrombocythemia, respectively.
PAN, associated with hepatitis B infection in some patients, is a vasculitide that manifests as aneurysmal nodules along the walls of middle-sized arteries. The key clinical features of the disorder include:
Other manifestations that may be present include:
Corticosteroid and cytotoxic drugs are the mainstay of therapy in PAN. It is possible to achieve permanent remission of the disease, despite potential complication such as atherosclerosis.
CPAN, as the name implies, is limited primarily to the skin. It clinically presents with fever and subcutaneous lesions, found mostly on the lower extremities, which are nodular, purpuric and painful. There are usually no systemic features other than myalgia and joint pain.
Over the course of the disease there are cycles of exacerbations followed by remissions that may last for many years. There have been studies that suggest that CPAN does not progress to PAN, putting the two into entirely separate categories.
Such a distinction may be arbitrary, especially for patients who are initially diagnosed with CPAN, but fail to respond to standard treatment with non-steroidal anti-inflammatory drugs and/ or oral steroids, or who have more extensive clinical manifestations.
Treatment of the condition is usually with oral steroids, which help to achieve remission. Non-steroidal anti-inflammatory drugs help to control symptoms in a few patients. Intravenous immunoglobulin therapy is used if the condition fails to respond to usual treatment, or steroids produces unacceptable side effects.