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Seasonal Variations in Onset of Wegener's Granulomatosis: Increased in Summer? To the Editor: We read with interest the article by Mahr, et al reporting an excess of Wegener's granulomatosis (WG) presenting in summer months1. This contrasts with several previous reports of a winter predominance. The preponderance of onset of WG in the winter and reported cyclical fluctuations in incidence has led to the hypothesis that an infection may trigger disease. Possible explanations for the observed differences between studies include: a real heterogeneity in trigger factors between geographical areas; methodological discrepancies including case ascertainment; and the uncertainty in establishing an accurate date of onset of the disease process. As part of an epidemiological study of primary systemic vasculitis, investigating possible environmental factors involved in pathogenesis, we reviewed all patients diagnosed with WG (American College of Rheumatology 1990 criteria) within a well-defined population2,3. The date of the first symptom of WG and the date of diagnosis were established for 55 patients with WG diagnosed between January 1989 and July 2000 by case-note review and interview of 47 surviving patients. Details of the 51 patients whose symptoms of vasculitis began between January 1989 and December 1998 only were included in analysis to optimize case ascertainment, which could otherwise be underestimated due to delay between first symptom and diagnosis. Details of the annual fluctuation of influenza, mycoplasma pneumonia, parvovirus, and chlamydia for the Eastern Region of the UK were obtained from the public health laboratory services. Annual fluctuations in each infection were compared to annual fluctuations in the onset of WG using the Poisson distribution. Seasonal fluctuations were assessed by the chi-square test where seasons were defined as winter (December–February), spring (March–May), summer (June– August), and autumn (September–November). There was a nonsignificant trend (p < 0.5) towards a higher onset of WG in autumn (35.3% cases), winter (25.5%), and spring (23.5%), with a trough in summer (15.7%). Findings were similar for 37 patients diagnosed with microscopic polyangiitis (p < 0.1) or Churg-Strauss syndrome (p > 0.5). We also failed to find any significant associations between the first symptom of vasculitis and season of onset, although it was interesting to note a high number of patients whose first manifestation of vasculitis were ear, nose, and throat symptoms presented in November, December, and January. There were also no significant annual peaks or troughs in the onset of WG, microscopic polyangiitis, or Churg-Strauss syndrome, and annual fluctuations in infection rates did not correspond with nonsignificant fluctuations in vasculitis. Thus, in a well-defined population we have been unable to confirm the occurrence of a seasonal onset for WG or other types of primary systemic vasculitis. Unfortunately, although analysis of temporal variations in the onset of vasculitis offers a tantalizing insight into potential pathogenic trigger factors, studies are limited by methodological problems, especially full case ascertainment within well-defined populations, difficulty in establishing the actual onset of vasculitis, and small numbers of cases. SUZANNE E. LANE, MD, MRCP, Consultant Rheumatologist, Ipswich Hospital NHS Trust; RICHARD A. WATTS, DM, FRCP, Senior Lecturer, School of Medicine, Health Policy and Practice, University of East Anglia, Consultant Rheumatologist, Ipswich Hospital NHS Trust; DAVID G.I. SCOTT, MD, FRCP, Honorary Professor, School of Medicine, Health Policy and Practice, University of East Anglia, Consultant Rheumatologist, Norfolk and Norwich University Hospital Trust, Ipswich, UK. Address reprint requests to Dr. S. Lane, Ipswich Hospital, Rheumatology, Heath Road, Ipswich IP4 5PD, UK. E-mail: suzanne.lane@ipswichhospital.nhs.uk 2. Watts RA, Lane SE, Bentham G, Scott DGI. Epidemiology of systemic vasculitis — a 10 year study in the United Kingdom. Arthritis Rheum 2000;43:422-7. 3. Lane SE, Watts RA, Bentham G, Innes N, Scott DGI. Are environmental factors important in primary systemic vasculitis? A case-control study. Arthritis Rheum 2003;48:814-23. |