[Infection and vascular purpura].

Palpable purpura is the hallmark of cutaneous vasculitis. Small-vessel vasculitis is a common vasculitis manifestation associated with acute or chronic infection. It is also characteristic of a systemic disease whether infectious or not. The pathogenic mechanisms appear to be complex: immune complex formation, vessel damage or altered vessel function mediated directly by infectious agents, humoral or cellular immunologic response. It is also a reaction to mixed cryoglobulinemia. Diagnosis of cutaneous vasculitis is simple (palpable purpuric eruption, nodules, vesiculobullous lesions, ulcerations), but etiological investigation is often difficult because the infectious origin is only rarely demonstrated. This type of purpura occurs in bacterial endocarditis and therefore blood cultures must be performed in any febrile patient particularly in the presence of a cardiac murmur. In fact the viral, parasitic or bacterial infectious origin is demonstrated in less than 30% of the cases of leucocytoclastic vasculitis. While focal sepsis is often found and its eradication should be followed-up, its role has not been proven particularly as antibiotics alone themselves can cause hypersensitivity vasculitis. Finally, mention must be made of virus induced vasculitis (B and C hepatitis, cytomegalovirus, parvovirus), antiviral treatment which permits better control of vasculitis.