Idiopathic uric acid lithiasis: epidemiologic and metabolic aspects.

Of 264 patients with urolithiasis those with pure uric acid or urate stones were compared to those with other types of calculi for differences in epidemiologic factors and uric acid, calcium and phosphate metabolism. Patients with uric acid stones were predominantly older men. These patients had comparatively lower incomes and spent less money on food but consumed more alcohol. The urinary pH was lower than in the other groups. The absence of abnormally elevated serum uric acid levels and elevated 24-hour urinary uric acid excretion suggests this variety of uric acid lithiasis to be idiopathic in nature. This finding is supported by the results of standardized oral purine loading, which showed no post-loading differences in serum levels and revealed urinary concentrations in 12 patients with pure uric acid stones and 10 normal subjects. However, there is evidence to suggest that this condition may be a precursor of primary gout. Hereditary mechanisms are absent and the relapse rate is the same as in patients with other stones. Therefore, our results suggest the existence of an idiopathic variety of uric acid lithiasis that, at least in central Europe, occurs more frequently than previously assumed. The condition is not inherited, alcohol consumption is a major etiologic factor and there is no evidence of a causative role of abnormalities in purine metabolism.