Benefits of anaemia treatment on cognitive function

The role of anaemia in the pathogenesis of abnormal cognitive function in h aemodialysis patients is only partly understood. Several contemporary studi es have assessed cognitive function in haemodialysis patients using neurops ychological and neurophysiological tests, comparing the results obtained ov er a wide range of haematocrits before and after treatment with epoetin. Of the neurophysiological tests, which measure electrical impulses from the b rain in the presence or absence of specific stimuli, the cognitive event-re lated potential (ERP) has been particularly useful in evaluating this issue . Changes in amplitude (increase) and latency (decrease) of a specific wave form (P300) seen in the ERP correlate with improved cognitive function in haemodialysis patients following initiation of dialysis therapy. Similar ef fects are also evident when haematocrit is increased. Marsh et al. (Kidney Int 1991; 39: 155-163) examined the effect of increasing haematocrit with e poetin therapy on the P300 amplitude and latency, and noted that after incr easing haematocrit to 23.7-36% over 12 months with epoetin, P300 amplitude increased (P<0.025), and several neuropsychological test scores were signif icantly improved. Grimm et al. (Kidney Int 1990, 38: 480-486) found a signi ficant decrease in P300 latency and statistically nonsignificant improvemen ts in P300 amplitude when haematocrit was increased to 22.7-30.6%. Improvem ent in the electroencephalogram (EEG) and P300 latency has also been report ed by others, including Sagales et al. (Kidney Int 1993; 44. 1109-1115). Th e effect of complete reversal of anaemia (haematocrits 31.6-42.9%) on cogni tive function was recently revealed by Pickett et al. (Am J Kidney Dis 1999 ; 33: 1122-1130), who found improvement in several cognitive ERP manoeuvres and a significant decrease in EEG slowing (P<0.02) at higher haematocrits. Taken together, these various studies suggest that graded increments in ha ematocrit following epoetin therapy have a progressive effect on improving cognitive function in haemodialysis patients.