5.1.1 Allergic vasculitis

Allergic vasculitis is a small vessel damage, usually caused by immune complex deposition in postcapillary venules (Type III reaction of the Gell and Coombs classification), leading to palpable purpuric lesions.

Deposition of immune complexes (variable amounts of antibodies and antigens in their proportion to each other) in the small vessel walls, leads to complement activation, activation of granulocytes and extravasation (leucocytoclasia) and finally microthrombosis of the small vessels.

Triggers include infections (HIV, HCV, bacteria), autoimmune and inflammatory diseases (connective tissue disease, ANCA-associated vasculitis, inflammatory bowel disease), medications, tumor associated antigens (solid tumors, haemotological). In almost 50% of the cases no trigger is found.

Frequent triggering factors are:

1. Medications

2. Infections: bacteria (especially streptococci), viruses (e.g., hepatitis C, HIV).

3. Chronic inflammatory and autoimmune diseases such as connective tissue diseases, inflammatory bowel disease, ANCA-associated vasculitis (granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis). Special variant: Schönlein-Henoch purpura (primarily in children) with deposition of IgA immune complexes.

4. Malignancies: myeloproliferative disorders, lymphomas, multiple myeloma.

Initial symptoms of allergic vasculitis include palpable purpura, which may later become necrotic and sometimes urticarial and nodular lesions. Internal organ involvement (kidneys, GI tract, joints, nervous system) with corresponding symptoms may occur. Arthralgia, low-grade fever and abdominal pain may be present in Schönlein-Henoch purpura.

In allergic vasculitis, first of all, systemic involvement should be assessed and a potential underlying disease should be determined.

• Parameters reflecting internal involvement: urinalysis (proteinuria, urine cytobacteriology), elevated creatinine levels, BUN, faecal occult blood, liver function, complete blood count and platelets count.

• Parameters reflecting inflammation: C-reactive protein, erythrocyte sedimentation rate, leukocyte count.

• Parameters reflecting aetiology: CBC with differential, platelet count, antistreptolysin antibody titre, hepatitis serologies (VHB, VHC), HIV test, ANA, anti-dsDNA antibodies, anti-extractable nuclear antigens antibodies, complement levels, RhF, ANCA, IgA, cryoglobulinemia, blood cultures in any case of suspicious endocarditis, ASCA.

Early stages may show perivascular lymphocytes, macrophages and apoptotic leucocytes (“leucocytoclasia”, nuclear dust). Eosinophilic granulocytes may be present. Postcapillary venules may have swollen endothelia with fibrin deposition leading to erythrocyte extravasation. Microthrombosis of the small vessels may cause necrosis of the surrounding tissue.

IgG and IgM deposition may be found by direct skin immunofluoresecence, whereas IgA deposition is more characteristic of Schönlein-Henoch purpura.

Allergic vasculitis is diagnosed based on the clinical manifestations and skin histology. Laboratory tests (renal and aetiological workup) are also required as well as imaging of the inner organs depending on the clinical presentation (abdominal sonography or tomodensitometry).