Pain threshold and tolerance in Alzheimer's disease

We tested both pain thresholds and pain tolerance in patients with Alzheimer'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 ischemia was studied. By comparing AD patients with normal subjects of the same age, we found no differences in stimulus detection and pain thresholds, whereas 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). There was a straightforward correlation between MMSE scores and pain tolerance such that the more severe the cognitive impairment the higher the tolerance to pain. In addition, analysis of the EEG power spectra indicated that patients with low alpha and high delta peaks showed an increase in pain tolerance to both electrical stimulation and ischemia. These findings show that, whereas the sensory-discriminative component of pain 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 disease according to the rule, 'the more severe the MMSE and EEG changes, the higher the tolerance to pain'.