Neurobiology of Pain

There often exists the pretense that age dulls the sense of pain. Along with this sentiment, there is the belief that old people are less sensitive to the effects of pain. There have been many studies conducted examining the pain threshold responses of the elderly to a variety of noxious stimuli (Gibson and Helme 2001). The results have provided interesting insights on the neurobiology of pain evolution in the aging population.

Psychophysical studies of heat pain thresholds in young and older adults have revealed age-related increases in thermal pain threshold. A 20% increase in radiant pain threshold has been observed for most elderly patients, particularly those greater than 70 years of age.

Additionally, studies have revealed modest increases in pressure and sharp pain thresholds, 15 and 20%, respectively (Gibson and Helme 2001).

Visceral pain thresholds have also been studied in the elderly. There is a significant age-related increase in pressure pain threshold of visceral tissue (Gibson and Helme 2001). For example, gastric and esophageal distension studies (with an inflatable balloon) have shown a 50% increase in reported visceral pain among older individuals (Gibson and Helme 2001). This may partially explain the diminished and atypical pain presentations for common organ system pathology (i.e., myocardial infarction) in this patient population.

Descending neuro-inhibitory pathways have also been studied in the elderly population. Studies directed at activating these endogenous analgesic systems (i.e., repeated ice water immersion) have revealed that post-exposure analgesic responses (measured by postexposure pain threshold responses) are markedly reduced in persons of advanced age. For example, elderly patients were found to have only a 40% increase in pain threshold after repeated ice water immersion as compared to a 150% increase as seen in younger adults (Gibson and Helme 2001). This may explain some of the age variations in reported pain tolerance levels and the ability to cope with severe or chronic persistent pain.

Studies in the elderly have demonstrated clear associations between pain perception and mood disorders. Patients who are anxious or depressed voice more localized and intense pain than do their non-anxious/non-depressed counterparts (Berger 2007). Given the fact that mood disorders are increasingly prevalent in the elderly population (i.e., prevalence of major depressive disorder 1-2% in community-dwelling elderly and 5-6% in older patients in the primary care setting), it is especially important to recognize co-morbid psychiatric disease in this patient population. Sometimes adequate pain control can be achieved from simple psychological or psychiatric interventions.

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