Uric acid and cognition in Parkinson's disease: a follow-up study.

Cognitive changes are common in Parkinson's disease (PD). Low plasma uric acid (UA) level is associated with risk of PD and predicts faster progression of motor symptoms in established disease. Whether UA levels predict cognitive changes has not been studied. In a crossectional study, our group has previously shown an association of plasma and urine UA levels with cognition in PD. The aim of the present controlled longitudinal study was to examine the evolution of cognitive changes and the prognostic value of the UA levels on cognition in the previously reported PD-patient cohort. Of the original 40 patients, 31 were available for follow-up after three years. Both plasma and daily urine UA levels were measured, nutrition was evaluated using 4-day dietary recall diary and cognition was assessed by a thorough neuropsychological examination including computerized tasks with Cognispeed©. The plasma and urine UA levels of the patients remained stable during the follow-up. At the same time, the rate of cognitive decline was unexpectedly slow. A statistically significant deterioration was noted in verbal fluency (p=0.04) and in Cognispeed©'s vigilance task (p=0.0001). In forward linear regression analysis only the baseline daily urine UA level contributed to verbal fluency (p=0.01), picture completion (p=0.001), block design (p=0.006), vigilance (p=0.006), subtraction (p=0.01) and statement verification (p=0.04) tasks. The implications of the study results are discussed.