Pain and cognitive impairment: from sensory indifference to neurodegenerative phenotype

OBJECTIVE: To systematize and analyze modern scientific data on pain sensitivity in patients with cognitive impairment, focused on its potential value as a neurophysiological biomarker of neurodegeneration. MATERIAL AND METHODS: A targeted review of peer-reviewed papers available in the PubMed, Scopus, Web of Science, and Google Scholar databases was conducted, mainly since 2015. The review includes original studies, systematic reviews, and meta-analyses on pain sensitivity in dementia, neurophysiological aspects of pain perception, and pathophysiological mechanisms linking chronic pain to neurodegenerative processes. RESULTS: The review revealed a paradoxical dissociation between a decrease in complaints of pain and a persistent or enhanced neuronal response to pain stimuli in patients with dementia. Major mechanisms include prefrontal cortex dysfunction, impaired downward pain modulation, neuroinflammation, and glial activation. Clinically, they manifest as an increase in pain thresholds along with an increase in the affective component of pain, leading to underdiagnosis and inadequate therapy. CONCLUSION: The change in pain sensitivity in patients with cognitive impairment is not a quantitative reduction, but a qualitative dysregulation of pain perception. This phenomenon reflects the neurodegeneration severity and may serve as a promising biomarker for dementia. Longitudinal studies and the development of standardized assessment methods are required for its clinical validation.