Chronic pain, depression link presents 'chicken or the egg' puzzle
SAN DIEGO — Although chronic pain impacts more than 100 million patients in the United States, contributing significantly to national medical costs, clinicians continue to struggle with whether pain represents a symptom or the disease itself, according to a presenter at the 2019 Congress of Clinical Rheumatology West.
“One of the concepts that I want to get across is that chronic pain is different from acute pain,” Robert W. Hurley, MD, PhD, director of the division of pain medicine at the Wake Forest Baptist Medical Center, told attendees. “Acute pain is the result of a specific injury, which, part of the definition is that the injury heals and goes away. Chronic pain is different in that it is persistent — it can last more than 3 months or it can last 25 years.”
In the U.S. alone, Hurley noted, chronic pain generates approximately $293 billion in direct medical costs; management for back pain represented 72% of these costs. Additionally, chronic pain also represents the top causes for “years lived with disability” and “disability-adjusted life years” among patients in the U.S., he said.
“Part of the question about chronic pain is how does this occur?” he said. “What are the actual differences between types of pain? One of the key differences may be that chronic pain is, in and of itself, a disease. If you look at the Merriam Webster dictionary definition of disease, chronic pain falls within the definition; its maladaptive with anatomical, physiological, pharmacological and psychological changes.”
In fact, Hurley noted, these very changes may be the reason “why a medication like duloxetine or [tricyclic antidepressants] can actually relieve chronic pain, while doing absolutely nothing for acute pain.”
However, Hurley emphasized that a key challenge is that clinicians are often unable to establish that these changes actually occur in their patients with chronic pain. The first instinct is to correlate observations and “we may incorrectly correlate or associate causes and effects.”
“For chronic pain, we are stuck looking at patients, doing functional studies, such as fMRI, and trying to subtract out all those other things that pain also causes when it is experienced for long periods of time,” Hurley said. “This is really a ‘chicken or the egg’ puzzle, trying to tease out what was preexisting. Did their depression cause the pain or did the pain cause the depression? Did the depression cause the changes in the fMRI signals or was it the pain?”
He noted, “Rarely am I a lumper vs. a splitter, but this is one of those cases it is much more a lumping. It is very hard to dissociate the psychological impact resulting in physiologic, pharmacologic or anatomic change from the pain itself.”– by Robert Stott
Hurley RW. Centralized pain in the rheumatologic patient. Presented at: Congress of Clinical Rheumatology West; September 26-29, 2019; San Diego.
Disclosure: Hurley reports no relevant financial disclosures.