Introduction
Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis comprises a heterogeneous group of vasculitides characterised by inflammation and necrosis of small and medium-sized vessels, usually associated with autoantibodies directed against neutrophil lysosomal enzymes (1).
Consensus statements on testing methods, clinical indications and interpretation of ANCA tests have been published (2). However, the usefulness of monitoring ANCA levels in the clinical follow-up of AAV is still a matter of debate. Most studies have focused on analysing the sensitivity, specificity, and predictive value of an increase in ANCA levels to predict clinical relapses. The results of these studies vary widely, probably related to the heterogeneity of the vasculitides included, the criteria used to define an increase in ANCA titres, and the criteria used to define a clinical relapse (3). At present, most clinicians continue to routinely monitor ANCA levels, although several studies have claimed that there is no need to perform such serial measurements since they have a low sensitivity and specificity to predict a clinical relapse (4-7).
Long-term observation of patients with AAV allows the identification of different patterns of ANCA titers during follow-up. Some patients will display a monophasic pattern, with an initial peak of antibodies that later become negative, while others will present persistent low levels, or recurrent peaks, or will remain with persistently high ANCA levels. The present study aimed to characterise these longitudinal patterns and to determine their clinical assocations and possible prognostic impact.