Seasonal variation in the onset of acute microcrystalline arthritis

Objective. To determine whether acute attacks of uric acid acid calcium pyr ophosphate microcrystalline arthritis show a seasonal variation and, if so, to verify whether the distribution of single episodes shows a rhythmic cir cannual pattern. Method. All suspected cases of microcrystalline acute arthritis observed at the General Hospital of Ferrara during an 8 yr period (January 1990-Decemb er 1997) were: considered; Diagnosis was made on the basis of history, phys ical examination and analysis of synovial fluid by means of polarized light microscopy. Month and day of each event were categorized both into four 3- month periods (by seasons) and 12 monthly intervals. Two different statisti cal methods have been utilized: chi(2) test for goodness of fit and partial Fourier series. Results. During the period considered, 210 episodes of acute gout were obse rved [196 in males (93.3%) and 14 in females (6.7%)] in 179 different subje cts, and 179 episodes of acute pseudogout [58 in males (32.4%) and 121 in F emales (67.6%)] in 165 different subjects. Gout attacks showed a higher fre quency peak in spring [76 cases (36.2%), P <0.001]. Analysis of distributio n of events by gender confirmed the clear spring pattern in males (36.2%), whereas the paucity of cases in females did not allow any valid statistical analysis. Pseudogout attacks showed a higher frequency peak in autumn [52 cases (29.1%)], without reaching a statistically significant level either f or the total sample or for subgroups divided by gender. Analysis of the sea sonal distribution of gout or pseudogout events was significantly different (chi(2) 15.7, P = 0.001). Chronobiological evaluation by means of Fourier analysis showed a circannual pattern for gout attacks, both for the total s ample (P = 0.006) and the male subgroup (P = 0.003), characterized by a pea k in April and a trough in October. Again, as for pseudogout events, no sea sonal variation was found, either for the total sample or subgroups by gend er. Conclusions. The present study gives further confirmation that acute gout a ttacks exhibit a circannual distribution in their occurrence, being more fr equent in April, Whereas pseudogout attacks do not. Moreover, the seasonal distribution of gout and pseudogout acute events is significantly different .