Hypersensitivity vasculitis
Overview
Heterogeneous group of disorders characterized by a vasculitic syndrome presumed to be associated with a hypersensitivity reaction following exposure to an antigen such as an infectious agent, a drug, or other foreign or endogenous substance
Causes
It is usually due to a known drug (such as cefoperazone or nicoumalone, auto-antigens or infectious agents such as bacteria. Immune complexes lodge in the vessel wall, attracting polymorphonuclear leukocytes who in turn release tissue-degrading substances leading to an inflammatory process.
Diagnosis
An important differential is Henoch-Schönlein purpura. At least 3 out of 5 criteria yields a sensitivity of 71% and a specificity of 84%: * Age > 16. * Use of possible triggering drug in relation to symptoms. * Palpable painful purpura (the three P's). * Maculopapular rash. * Skin biopsy showing neutrophil infiltration around vessel.
Prognosis
The majority of cases are short-lived; in one paper around 60% of patients had symptoms resolving in less than months.The outlook will depend on the underlying cause. If none is found and only skin and joints are affected, the prognosis is good although recurrence is not uncommon
Treatment
The most important part of the treatment is to eliminate the cause of the vasculitis, if at all possible. Antihistamines prove helpful to some patients. If the vasculitis is damaging organ systems such as the kidneys, immunosuppressive agents are indicated.