5.1.1 Allergic vasculitis

Grading & Level of Importance: B


Leukocytoclastic vasculitis: 4A44.B


Hypersensitivity vasculitis; Immunologic type 3 vasculitis.


Allergic vasculitis is one of the most frequent forms of vasculitis.


Allergic vasculitis is caused by small vessel damage, usually via immune complex deposition in post-capillary venules.

Aetiology & Pathogenesis

Deposition of immune complexes (variable proportions of antibodies and antigens) in small vessel walls, leads to complement activation, granulocyte activation 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.

Signs & Symptoms

Initial symptoms of allergic vasculitis include purpuric, palpable, later necrotic lesions, including urticarial and nodular lesions. Internal organ involvement (kidneys, GI tract, joints, nervous system) may occur.


Lesions generally predominate on the distal extremities, preferentially on the legs.


Allergic vasculitis can be separated into purely cutaneous forms (single organ vasculitis) and systemic forms (multi-organ vasculitis).

Laboratory & other workups

Systemic (especially renal) involvement should be assessed and any underlying disease should be identified.


Early stages may show perivascular lymphocytes, macrophages and apoptotic leucocytes (“leucocytoclasia”, nuclear dust), fibrin deposition in the vessel wall and sometimes microthrombosis of the small vessels. Usually erythrocyte extravasation occurs. IgG and IgM deposition may be found by direct skin immunofluorescence. IgA deposition is more characteristic of Schönlein-Henoch purpura.


The course of allergic vasculitis may be acute, subacute, chronic or recurrent.


Allergic vasculitis may affect internal organs depending on the underlying cause. Renal and digestive involvement may characteristically occur in Schönlein-Henoch purpura. 


Allergic vasculitis is diagnosed based on the clinical manifestations and skin histology. Laboratory tests (renal and aetiological workup) are also required depending on the clinical presentation.

Differential diagnosis

Differential diagnoses of allergic vasculitis include thrombotic diseases (cryoproteinemia, antiphospholipid syndrome, cold agglutinins), thrombocytopenia clotting factor deficiency, including anti-coagulants, embolic disorders (cholesterol emboli, atrial myxoma) and septic-embolic diseases (endocarditis).

Prevention & Therapy

Avoidance of triggers, bed rest, medication (systemic corticosteroids) depending on the etiology and internal organ involvement. Anti-coagulants in some specific cases.



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