Association between urine protein/creatinine ratio and cognitive dysfunction in Lewy body disorders

Background Impaired renal function and proteinuria have been associated with cognitive impairment and dementia. Chronic kidney disease is considered to be an independent risk factor for Lewy body spectrum disorders (LBD). However, few studies have mentioned an association between proteinuria and cognition in LBD. We investigated the relationship between proteinuria and cognitive dysfunction in patients with Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Methods Among 186 patients with LBD, 53 had PD-normal cognition (PD-NC), 76 had PD-mild cognitive impairment (PD-MCI), 43 had PD-dementia (PDD) and 14 had DLB. The urine protein/creatinine ratio was calculated using the spot urine test and brain magnetic resonance scans was obtained in all patients. Results The urine protein/creatinine ratio was significantly higher in patients with PDD and DLB than in those with PD-MCI, PD-NC patients and healthy controls, and was correlated with white matter hyperintensities on magnetic resonance imaging. All abnormal neuropsychological test results were associated with increased urine protein/creatinine ratio. After controlling for age, education, symptom duration, diabetes mellitus, hypertension, and parkinsonian motor severity, the urine protein/creatinine ratio was significantly associated with decreased cognition. Conclusion The urine protein/creatinine ratio was associated with cognitive status in LBD. These finding suggests that increased protein excretion is associated with cognitive dysfunction in patients with LBD.