Contact heat sensitivity and reports of unpleasantness in communicative people with mild to moderate cognitive impairment in Alzheimer’s disease: a cross-sectional study

BACKGROUND Compared to healthy controls, people with Alzheimer's disease (AD) have been shown to receive less pain medication and report pain less frequently. It is unknown if these findings reflect less perceived pain in AD, an inability to recognize pain, or an inability to communicate pain. METHODS To further examine aspects of pain processing in AD, we conducted a cross-sectional study of sex-matched adults ≥65 years old with and without AD (AD: n = 40, female = 20, median age = 75; control: n = 40, female = 20, median age = 70) to compare the psychophysical response to contact-evoked perceptual heat thresholds of warmth, mild pain, and moderate pain, and self-reported unpleasantness for each percept. RESULTS When compared to controls, participants with AD required higher temperatures to report sensing warmth (Cohen's d = 0.64, p = 0.002), mild pain (Cohen's d = 0.51, p = 0.016), and moderate pain (Cohen's d = 0.45, p = 0.043). Conversely, there were no significant between-group differences in unpleasantness ratings (p > 0.05). CONCLUSIONS The between-group findings demonstrate that when compared to controls, people with AD are less sensitive to the detection of thermal pain but do not differ in affective response to the unpleasant aspects of thermal pain. These findings suggest that people with AD may experience greater levels of pain and potentially greater levels of tissue or organ damage prior to identifying and reporting injury. This finding may help to explain the decreased frequency of pain reports and consequently a lower administration of analgesics in AD.