29th January 2024

Background of vasculitides

Vasculitides are a heterogeneous group of relatively uncommon autoimmune diseases. There are many types of vasculitis, which can vary greatly in symptoms, severity and duration. They are linked by the presence of vascular inflammation, which can lead to vessel wall destruction, causing aneurysms or rupture, or stenosis of the vessel and resultant tissue ischaemia and necrosis. While the inflammatory process may be confined to one organ, it may also involve several organ systems. 

Patients will typically present in one of three ways. Many will have only constitutional and non-specific symptoms such as malaise, weight loss or fever; this can often be mistaken for an infective picture, especially when associated with raised inflammatory markers. Others will develop specific organ manifestations; for example, patients may present with joint pain, erythema nodosum, renal failure, weakness or abdominal pain. Occasionally, a suspicion of vasculitis may be identified incidentally, such as in those with microscopic haematuria. Vasculitis should be considered in patients presenting with palpable purpura, pulmonary infiltrates, unexplained ischemic events and multisystem disease. 

Vasculitis may occur as a primary disease (idiopathic) or a secondary response to an underlying disease (e.g. hepatitis B infection). We do not know what causes most types of vasculitis, but genetic factors are likely significant. Vasculitis can be a part of other rheumatic diseases, including systemic lupus erythematosus, rheumatoid arthritis and Sjögren’s syndrome. 

Common blood tests used in the diagnosis and management of vasculitis 

• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) – these inflammatory markers are frequently raised at presentation. They are also useful to monitor disease activity in response to treatment.
• Antineutrophil Cytoplasmic Antibodies (ANCA) – are antibodies raised against antigens in the cytoplasm of neutrophil granulocytes. Antigens for p ANCA include myeloperoxidase (MPO) and bacterial permeability-increasing factor. The c-ANCA antigen is specially proteinase 3 (PR3). The presence of PR3 and MPO antibodies are highly important in the diagnosis of ANCA-associated vasculitis. 
• Antinuclear antibody (ANA) – this is an antibody which targets the nuclear components of the cell. It is non-specific and, therefore, not often used for diagnosis of vasculitides but can be an indicator of underlying autoimmune processes.
• Complement levels – the complement cascade is part of the immune system that allows antibodies and phagocytic cells to clear microbes and damaged cells from an organism. In immune-mediated vasculitis, the complement cascade enhances the ability of autoantibodies and phagocytic cells to clear damaged cells. In acute vasculitis, complement C3 and C4 levels are often reduced and normalised as a response to treatment. 

References

• About vasculitis, Vasculitis UK. Available at: https://www.vasculitis.org.uk/about-vasculitis [Accessed 28th January 2022].
• Clunie, G. P. R., Wilkinson, N., Nikiphorou, E., Jadon, D. (2018) Oxford Handbook of Rheumatology 4th edition. Oxford University Press
• Sofat, N., Rutter-Locher, Z., Oakley, H. (2021) Rheumatology – a case based approach to management. Scion Publishing limited 
• Vasculitides, Amboss. Available at: https://www.amboss.com/us/knowledge/Vasculitides/ [Accessed 17th January 2022].Vasculitis, American College of Rheumaology. Available at: https://www.rheumatology.org/I-Am-A/Patient-Caregiver/Diseases-Conditions/Vasculitis [Accessed 17th January 2022].
• Vasculitis, Versus Arthritis. Available at: https://www.versusarthritis.org/about-arthritis/conditions/vasculitis/[Accessed 15th January 2022].
• What is Vasculitis? Johns Hopkins Vasculitis Center. Available at: https://www.hopkinsvasculitis.org/vasculitis/  [Accessed 16th January]