345 ‒ Chronic pain: pathways, treatment, and the path to physical and psychological recovery

KEYPOINTS

• 01

  Pain is a biopsychosocial experience, not a simple wire to the brain.

  Mackey, chief of pain medicine at Stanford, says Descartes' 17th-century model—injury sends a signal straight to the brain—stuck for centuries and lingers today. Only in the last 20 years or so have surgeons widely accepted that what patients bring to the operating table, including early-life experiences, shapes how much pain they feel.

• 02

  Different nerve fibers carry different pain, and referral explains odd symptoms.

  Myelinated A-delta fibers transmit at about 10 m/s—roughly 10 times faster than unmyelinated C fibers—giving the sharp first pain before the dull ache. Bowel biopsies often don't hurt because those nociceptors don't respond to cutting; diaphragm irritation shows up as shoulder pain because both are served by C3–C5 ('C3, 4, 5 keeps the diaphragm alive').

• 03

  The spinal cord gates pain, so identical injuries feel different.

  Melzack and Wall's 1965 gate control theory explains why ten people with the same injury report different pain, and why TENS and other neuromodulation can work. In a study applying a 48°C stimulus to about 500 people, ratings ranged from 0 to 10; Mackey's ice-water demo with medical students shows the same spread.

• 04

  Emotion, beliefs and sleep turn the volume up or down.

  Mackey likens pain processing to a stereo amplifier set differently in each person. Peter notes his 42°F cold plunge sometimes feels like nothing for 10 minutes and sometimes makes his ankles scream after 30 seconds. Catastrophizing, a concept introduced by Albert Ellis in 1962, is a strong amplifier.

• 05

  Pain is evolutionarily essential.

  People who can't feel pain make dangerous decisions and historically didn't pass on genes; Peter jokes he doesn't understand why more young males didn't die before 20. Cultural norms also reward stoicism—Mackey's father, one of 13 children, brought that ethic home.

• 06

  NSAIDs and acetaminophen work best thoughtfully combined.

  NSAIDs and COX-2 inhibitors reduce the 'inflammatory soup' of swelling, redness and heat; Vioxx was withdrawn after FDA concerns. A combination of 400 mg ibuprofen and 500 mg acetaminophen three times daily worked well for Peter; naproxen at 500 mg twice daily is easier to line up. These are personal regimens discussed, not general prescriptions.

• 07

  Muscle relaxants and gabapentinoids have specific roles and side effects.

  Peter uses 2–3 days of baclofen 20 mg with a little NSAID to abort back flares; Mackey generally goes up to 20 mg three times daily orally, with intrathecal pumps for severe spasticity. Gabapentin and pregabalin act on the alpha-2-delta calcium-channel subunit; gabapentin absorption saturates around 900–1,000 mg per dose, so he doses lower by day and higher at night (e.g., 300/300/600), and warns elderly patients about falls. Pregabalin can cause weight gain.

• 08

  Chronic pain is enormous in scale.

  Mackey estimates 50–100 million Americans have chronic pain, about 8% (20+ million) with high-impact chronic pain; low back pain is the most common at about 28%.

• 09

  Opioids have a nuanced role, and the crisis had many parents.

  Mackey criticizes how a brief letter to the New England Journal claiming little addiction was amplified by Purdue and others. Peter compares the crisis to the 2006–08 mortgage crisis: easy to blame one actor, but many contributed. Mackey's 2010 Institute of Medicine panel flagged the long-term effectiveness and safety of opioids for chronic pain as a top unanswered question.

• 10

  Low-dose naltrexone is a promising, cheap option for fibromyalgia and beyond.

  At 50 mg naltrexone blocks opioid receptors; at about 4.5 mg it appears to block toll-like receptor 4 on microglia, calming neuroinflammation. Mackey has gone up to 13.5 mg in some patients. About 20–30% get vivid 'technicolor' dreams; if it's activating, take it in the morning. It must usually be compounded.

• 11

  Peter recovered from 320 mg/day of OxyContin to full function.

  A 5 cm disc fragment sat on his S1 nerve root; he was taking about 320 mg of OxyContin daily—enough, he says, to kill two people today—to blunt emotional as well as physical pain. Mackey later gave him 400 mg of IV lidocaine over 20 minutes under EKG monitoring, followed by precise injections at T12–L1 facets over 3–4 months, and gabapentin he tapered off within 18 months.