Seasonal variation in the onset of acute microcrystalline arthritis.

OBJECTIVE: To determine whether acute attacks of uric acid and calcium pyrophosphate microcrystalline arthritis show a seasonal variation and, if so, to verify whether the distribution of single episodes shows a rhythmic circannual pattern.
METHOD: All suspected cases of microcrystalline acute arthritis observed at the General Hospital of Ferrara during an 8 yr period (January 1990-December 1997) were considered. Diagnosis was made on the basis of history, physical 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 statistical 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 observed [196 in males (93.3%) and 14 in females (6.7%)] in 179 different subjects, and 179 episodes of acute pseudogout [58 in males (32.4%) and 121 in females (67.6%)] in 165 different subjects. Gout attacks showed a higher frequency peak in spring [76 cases (36. 2%), P<0.001]. Analysis of distribution 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 for the total sample or for subgroups divided by gender. Analysis of the seasonal 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 sample (P=0.006) and the male subgroup (P=0.003), characterized by a peak in April and a trough in October. Again, as for pseudogout events, no seasonal variation was found, either for the total sample or subgroups by gender.
CONCLUSIONS: The present study gives further confirmation that acute gout attacks exhibit a circannual distribution in their occurrence, being more frequent in April, whereas pseudogout attacks do not. Moreover, the seasonal distribution of gout and pseudogout acute events is significantly different.