Evidence-Based Reviews

Does chronic pain shrink the brain?

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Chronic pain—particularly lower back pain—is frustrating to both patient and clinician. Because most cases lack an obvious physical explanation, the doctor may wonder if the patient is faking or exaggerating—that the pain is “in the patient’s head.” Studies suggest this cerebral component may exist—but not in ways you might expect.

How the brain processes pain

According to traditional belief, the brain passively receives noxious signals from injured tissue (nociceptive) or damaged nerve (neuropathic). Extensive—some would say excessive—tests are often conducted in search of a bone or muscle injury that might explain the pain.

Functional imaging studies across 15 years have shown activity in various brain regions when subjects feel pain. In addition to the somatosensory cortex, pain also activates brain areas involved with mood, attention, and anxiety. More important, the brain does not passively receive signals from the periphery but can inhibit ascending signals with endogenous opioids, such as endorphins and enkephalins.

Apkarian et alPosttraumatic stress disorder: Nature and nurture?, May 2004.)

Drugs. Medications and other substances taken to alleviate pain might also reduce gray matter. Excessive alcohol and opioid use have long-term adverse effects on the CNS.3 Is treatment or self-medication mildly toxic to the brain?

Overuse atrophy. Apkarian et al1 propose that cortical loss may be secondary to overuse. They suggest that persistent pain perception— and the resultant negative affect and stress—causes an excitotoxic and inflammatory state that wears out portions of the brain circuitry. If this is true, then chronic pain itself causes cerebral atrophy.

Whatever the explanation, this study indicates that chronic lower back pain pathology extends beyond the lower back.

Related resources

  • Deyo RA, Weinstein JN. Low back pain. N Engl J Med 2001;344:363-70.
  • International Association for the Study of Pain. www.iasp-pain.org.

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