Vasculitis

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The term vasculitis refers to inflammation of blood vessels and represents a heterogeneous group of clinical disorders.

Each form of vasculitis can produce a distinct clinical picture, but in many cases immunology testing can differentiate, confirm and monitor the presence of vasculitis. Other forms of vasculitis, for example, Behçet’s disease and primary cerebral vasculitis are not associated with any specific blood tests.

The main immunological tests are Antinuclear antibody (ANA – for SLE a connective tissue diseases) and Anti-neutrophil cytoplasmic antibody (ANCA – Wegener’s granulomatosis and other vasculitides).

It is important to understand that neither of these tests is specific; they can both be positive in infection and in liver disease. This makes these tests very unsuitable as ‘screens’ in patients with vague symptoms such as malaise, weight loss or fever.

Other tests include Complement C3 and Complement C4, which are altered in immune complex disease and cryoglobulin.

Small vessel hypersensitivity vasculitis

Relevant immunological tests:

Infection, drugs, foreign proteins (as examples) may be causal factors in a vasculitis affecting predominantly the skin.

Immunological findings may sometimes include raised ESR/CRP, depressed levels of complement factors suggesting consumption, and the presence of antinuclear antibodies and rheumatoid factor (low titre).

General screening tests for vasculitis should also include serum immunoglobulins, and ANCA.

If there is evidence for more extensive visceral involvement, one of the primary systemic vasculitides may be involved.

Alternatively, the vasculitis may be secondary to autoimmune disease (eg. SLE, chronic active hepatitis), neoplasia (eg. lymphoma), cryoglobulinaemia (these are immunoglobulins that form precipitates in the cold).

Primary systemic vasculitis

Relevant immunological tests:

Some forms of systemic vasculitis are strongly associated with circulating anti-neutrophil cytoplasmic antigens (ANCA).

In Wegener’s Granulomatosis, (WG) (lung, renal) there is a diffuse cytoplasmic pattern (c-ANCA), as well as polyclonal elevations of IgG, IgA, IgE and raised CRP.

ANCAs with a perinuclear pattern (p-ANCA) are seen in some patients with polyarteritis nodosa, (PAN) (weight loss, musculoskeletal, renal) and Churg-Strauss (“asthma”, eosinophilia, hypocomplemenaemia, raised IgE).

Both types of ANCA may be seen in microscopic polyarteritis (MPA) (clinical overlap between classic PAN and WG).

Atypical forms of ANCA reactivity may be seen in association with Henoch-Schönlein Purpura (sometimes IgA raised), Kawasaki’s syndrome, and in other autoimmune disorders (eg. SLE, ulcerative colitis).

 

(Last reviewed September 2024)