In Rheumatology, Not all Pain is Created Equal

All pain is not created equal and treating it as if it is all the same may lead doctors to miss the most important reasons why patients are hurting, according to Daniel Clauw, M.D., a rheumatologist and the director of the Chronic Pain and Fatigue Research Center at the University of Michigan.

Dr. Clauw reviewed the status of pain research at the winter symposium of the American College of Rheumatology in Snowmass, Colorado in January. He highlighted the differences between peripheral nociceptive pain, peripheral neuropathic pain and centralized pain - traceable to disturbances in central nervous system pain processing - and the treatment mechanisms that can be used for each. Patients often experienced mixed states of all three pain types, running along of spectrum of mostly nociceptive (acute pain or osteoarthritis) to mostly centralized (fibromyalgia).

Rheumatology Network interviewed Dr. Clauw via email to learn more about these pain states and how to treat them.

1. Why is it important to understand the mechanisms underlying pain?

Historically most chronic pain conditions were named based on their location in the body (e.g. headache, low back pain, TMJ Disorder). We now know that pain in any location in the body can occur because of a problem in that area of the body (this is called nociceptive pain), because there is damage or entrapment of nerves that bring information from that body region (nerve or neuropathic pain), or because the central nervous system (i.e. brain and spinal cord) is amplifying pain and other sensory experiences throughout the body (centralized pain).  It appears as though treating pain based on which of these underlying mechanisms is causing the pain is more effective than thinking that any pain coming from any single body region should be treated the same.   

2. What is centralized pain?  

Centralized pain is pain that is occurring because the central nervous system is turning up the volume control on pain and other sensory experiences throughout the entire body. Thus the primary characteristic of centralized pain is that individuals have pain in multiple body regions at any given time - and over the course of their lifetime.  Individuals with centralized pain also have other symptoms coming from the central nervous system such as fatigue, sleep and memory problems, and sensitivity to other sensory experiences (they find lights to be brighter, noise louder, odors more bothersome).   

3. How does centralized pain present clinically? Does it often overlap with nociceptive pain states? 

It is very common for people to have both nociceptive pain (i.e. pain due to some ongoing inflammation or damage) and superimposed centralized pain. When that occurs, both types of pain mechanisms need to be treated. Nociceptive pain responds well to anti-inflammatory drugs, surgery, injections and even opioids, whereas centralized pain does not respond to any of these treatments.

4. In your talk, you mentioned the possibility that the endogenous opioid system might cause the progression from acute pain to centralized pain - could you discuss a little bit about why this is a concern? 

Opioids do not work for centralized pain, and there is some evidence that the body’s own internal opioid system might be contributing to centralized pain. It seems that many people with centralized pain are actually made worse - slowly and gradually - by taking opioids.

5. Are there promising treatments for centralized pain out there or on the horizon?  

There are many effective drug treatments for centralized pain including tricyclic drugs, serotonin norepinephrine reuptake inhibitors and gabapentinoids. Other promising treatments that have not been as well studied include low dose naltrexone, cannabinoids and gammahydroxybutyrate.

Some of the most effective treatments for centralized pain are non-drug therapies.  Getting more active and low levels of exercise, and getting a good’s night sleep, are critical for people with centralized pain, since sleep and exercise are the body’s most effective analgesics.

If you would like to learn more about these treatments there are several free resources available including a Youtube video (https://www.youtube.com/watch?v=pgCfkA9RLrM ) on this topic, and a website our group developed: www.fibroguide.com. 

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References:

Daniel Clauw, M.D., PubMed published articles.