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Measuring disease activity and outcomes in clinical studies.

Untreated systemic vasculitis has an appalling prognosis. The pathogenesis is still being addressed, and we have no clear etiological agents defined in most cases of these uncommon but not rare diseases.1,2 Our lack of understanding of pathogenesis has led to the widespread use of classification systems, which describe groups of patients with different forms of vasculitis in predominantly pathological and clinical terms using vessel size as the dominant classification.3-5 These classification criteria are widely applied as diagnostic criteria, which is inappropriate since they do not serve this purpose well.6 In many ways, however, this distinction between different forms of vasculitis has served as the empirical basis for different forms of therapy.7 Large-vessel vasculitis is predominantly managed with steroid therapy alone, with the use of immunosuppressive drugs such as azathioprine or methotrexate only if there is resistance to steroids. By contrast, the small-vessel vasculitides, such as Wegener’s granulomatosis involving the kidney, or microscopic polyangiitis with kidney and lung involvement, are primarily managed by the use of cyclophosphamide and steroids. Therefore, at the classification or diagnostic stage we are already making a distinction between diseases that we treat more or less aggressively. As a further refinement of this process, within each disease it is becoming increasingly apparent that there is a need to distinguish the pattern of involvement in each individual case and the current level of disease activity, which might require different levels of immunosuppressive treatment at any point in time.8,9 This strategy leads to a more logical framework for addressing the need for appropriate immunosuppression. The concept that vasculitic diseases are a one-shot illness is no longer valid. We recognize that modern management has transformed the outcome for survival to a very high survival probability. However, survival is characterized by frequent episodes of reactivation of the original disease (in up to 50% of cases in some series) or persistent grumbling lowgrade disease.10,11 In addition, the chronic effects of disease scarring and drug toxicity take their toll and result in some cases in significant organ damage.12 Accurate assessment of disease activity is therefore an essential part of the management of these complex diseases. We need to discriminate between appropriate levels of immunosuppression and also distinguish active disease from chronic scarring for therapeutic strategies to be more appropriate. Disease assessment may also offer the opportunity to predict future outcome and is increasingly of use in determining how aggressive to be at disease onset.8 Therefore we must consider not only current levels of disease activity in their immediate context but also what they may be telling us of the likely future outcome. These are difficult tasks to expect any individual assessment to provide.