Pain threshold and tolerance in Alzheimer's disease

We tested both pain thresholds and pain tolerance in patients with Alzheime r's disease (AD) by means of phasic and tonic noxious stimuli. In the first case, electrical stimulation was used, whereas in the second case arm isch emia was studied. By comparing AD patients with normal subjects of the same age, we found no differences in stimulus detection and pain thresholds, wh ereas a clearcut increase in pain tolerance was present in AD patients. The severity of AD was assessed by means of the Mini Mental State Examination test (MMSE) and the spectral analysis of the electroencephalogram (EEG). Th ere was a straightforward correlation between MMSE scores and pain toleranc e such that the more severe the cognitive impairment the higher the toleran ce to pain. In addition, analysis of the EEG power spectra indicated that p atients with low alpha and high delta peaks showed an increase in pain tole rance to both electrical stimulation and ischemia. These findings show that , whereas the sensory-discriminative component of gain is maintained in AD patients, pain tolerance is altered and depends on cognitive and affective factors. Thus, pain tolerance is tightly related to the severity of the dis ease according to the rule, 'the more severe the MMSE and EEG changes, the higher the tolerance to pain'. (C) 1999 International Association for the S tudy of Pain. Published by Elsevier Science B.V.