Cognitive impairment in chronic kidney disease

BACKGROUND: Although end-stage renal disease (ESRD) has been associated with cognitive impairment, the relation between lesser degrees of chronic kidney disease (CKD) and cognitive impairment is less well understood. The objective of this study was to assess the cognitive function in patients with varying severity of CKD using P3 event-related potentials (P3ERPs). METHODS: In this cross-sectional study, 15 neurologically asymptomatic (Mini Mental State Examination >24) patients each of CKD stage 3, 4 and 5 (undialysed) were enrolled. Besides this, 15 healthy controls were also studied. All groups were age and sex matched. Glomerular filtration rate (GFR) was estimated using the Modification of Diet in Renal Disease equation. The P300 was studied in all subjects by using standard auditory 'odd-ball' paradigm and the data obtained were statistically analysed. RESULTS: We noted significant prolongation of P300 latencies as severity of CKD increased from stage 3 (318.8 +/- 28.98 ms) to stage 4 (357 +/- 24.65 ms) (P < 0.002) and from stage 4 to 5 (388.47 +/- 31.67 ms) (P < 0.01). P300 latency in CKD stage 3 was not found to be significantly different from controls (308.4 +/- 13.73 ms). Significant positive correlation was noted between serum creatinine, blood urea and uric acid with P3 latency. Significant negative correlation was noted between GFR, serum calcium and haemoglobin with P3 latency. CONCLUSIONS: Increasing severity of CKD is associated with progressive cognitive decline and this may have important clinical consequences.