Renal vasculitis in Japan and the UK-are there differences in epidemiology and clinical phenotype ?

Background. The epidemiology of renal vasculitis in different populations is poorly understood. A recent study from Japan suggests that whilst the overall incidence is similar to that reported from Europe, the clinical phenotype is different, with Wegener's granulomatosis being very much less common. The aim of this study was to compare the incidence of renal vasculitis in the UK with recent data from a Japanese population. Methods. Incident patients with renal vasculitis were identified prospectively between 2000 and 2004 from a well-defined UK population. The case notes were reviewed and clinical features extracted. Classification between Wegener's granulomatosis, microscopic polyangiitis and Churg Strauss syndrome was performed using a predetermined algorithm. Inclusion criteria were (i) new patients with vasculitis with or without histological confirmation, (ii) renal involvement and (iii) positive serology for anti-neutrophil cytoplasmic antibody (ANCA). Results. We identified 27 cases of renal vasculitis (Wegener's granulomatosis 13, microscopic polyangiitis 11, Churg Strauss syndrome 3) fulfilling the case definition. The overall average age was 63.5 years which is less than those of the Japanese patients. The overall annual incidence of renal vasculitis was 12.2/million similar to Japan. The annual incidence of Wegener's granulomatosis was 5.8/million, microscopic polyangiitis 4.9/million and Churg Strauss syndrome 1.4/million. ENT and neurological involvement were much less common in Japan. No patients with cANCA/PR3 were seen in Japan. Wegener's granumolatosis seems to be much less common in Japan than the UK. Discussion. Whilst the overall occurrence of renal vasculitis is similar in Japan to the UK, the clinical phenotype is very different with microscopic polyangiitis predominating in Japan.