Red blood cell/plasma choline ratio in elderly depressed and demented patients

In further study of red blood cell (RBC) and plasma choline concentrations in 160 elderly subjects, we found no significant differences in RBC/plasma choline ratios among depressed, demented, and healthy subjects. On the basis of a smaller sample, we had earlier reported that a significantly higher proportion of Alzheimer patients had RBC/plasma choline ratios greater than 1.9. Thus, it now appears that static RBC choline levels cannot be recommended as a specific marker of Alzheimer's dementia. However, within subgroups of these diagnostic categories, determined by RBC/plasma choline ratios less than or equal to 1.9 or greater than 1.9, consistent differences in electroencephalographic (EEG) sleep measures were found. The subgroup of demented patients with a RBC/plasma choline ratio greater than 1.9 was more impaired on the Blessed Dementia Rating Scale and had less rapid eye movement (REM) sleep than the subgroup with a choline ratio less than or equal to 1.9. Similarly, depressives with a choline ratio less than or equal to 1.9 had a lower REM latency than depressives with a choline ratio greater than 1.9. Finally, depressed-demented (i.e., mixed-symptom) patients with a choline ratio greater than 1.9 showed less sleep continuity disturbance but more indeterminate non-REM sleep (reflecting loss of spindles and K-complexes) than those with lower choline ratios. These differences parallel those previously reported for diagnostically "pure" depressed and demented patients, and they suggest a possible link between peripheral RBC/plasma choline measures and central nervous system function as reflected in sleep physiological alterations.