Can pain experience indicate one’s risk for Alzheimer’s disease?
What is Alzheimer's disease?
Alzheimer's disease is a neurodegenerative disorder, the most common cause of dementia. It causes brain atrophy and results in loss of memory and cognitive decline. The prevalence of dementia is expected to close to triple in the next three decades and early detection is important as it can contribute to better patient outcomes.
Connecting Alzheimer's disease with experimental pain
Several publications point to changes of the sensory system due to Alzheimers, from vision, olfactory, to sensory changes. In a recent paper (2021), Romano and colleagues aimed to investigate if one's response to experimental pain could serve as a non-invasive biomarker for Alzheimer's disease (AD) risk.
Forty-nine cognitively healthy subjects participated in the study. They were divided to subgroups by their apolipoprotein (APOE) allele genotype. Those who carry ε4 allele (APOE4) are considered to be at higher risk of late-onset AD. Twelve participants with APOE4 and thirty seven without this genetic marker performed the following thermal stimulation protocol: thermal stimulation was applied to their right hand and they were asked to press the button at either when they feel 'just noticeable pain', 'weak pain' or 'moderate pain', each perception assessed in a separate test. They were also asked to rate their unpleasantness at each of the above pain levels. The thermal stimulation was conducted using Medoc’s quantitative sensory testing (QST) device - Q-Sense.
Alzheimer's disease and pain sensitivity
The study results demonstrated that healthy individuals at a higher risk of late-onset AD (APOE4 positive genotype), are less sensitive to pain overall, but rated their pain to be more unpleasant, compared with APOE4 negative subjects.
The study results suggest that thermal pain testing may serve as a non-invasive phenotyping biomarker of increased risk for Alzheimer's disease in cognitively healthy individuals. Further investigation is warranted to confirm this finding and identify a specific pain pattern pointing to this genetic marker.