Nociceptive and Neuropathic Pain
Historically, almost all chronic non-cancer pain (CNCP) was thought to be either nociceptive or neuropathic. In this model of CNCP, the underlying cause of pain was believed to result from stimulation of peripheral pain or sensory nerve fibers located within the painful anatomic region. In this pain schema, peripherally directed therapies such as topical treatments, injections, opioids, and surgery are believed to be helpful. Examples of peripheral nociceptive pain include osteoarthritis, rheumatoid arthritis, and cancer pain. While examples of peripheral neuropathic pain include diabetic neuropathic pain and post-herpetic neuralgia.
However, over the past decade, a body of evidence has accumulated to suggest that a third type of pain, centralized pain, is likely to be much more prevalent than either nociceptive or neuropathic pain amongst working-age adults with CNCP. This distinction is very important to make as centralized pain, unlike nociceptive and neuropathic pain, is not responsive to peripherally directed therapies or opioids.16
Central Pain or Central Sensitization (CS)
The prototypical central pain state is fibromyalgia syndrome. But current research suggests that centralized pain is a spectrum disorder, which includes a large family of common chronic non-cancer pain diagnoses. Chronic low back pain, chronic headaches, and fibromyalgia are highly associated with CS.16,17,18
Screening for centralized pain syndromes is essential both for successful treatment and to avoid the unnecessary harms of over-medicalization with repeated scans, injections, surgeries, and opioids. Because the examination, imaging, and labs are often unremarkable in centralized pain syndromes, diagnosis rests upon a careful history, review of symptoms, and the use of validated CS screening instruments. Moreover, given the high co-occurrence of depression, anxiety, PTSD, and addictive disorders within individuals with CS, it is recommended that screening for these co-morbidities is also included in the initial evaluation.
If we treat centralized pain syndromes with drugs alone, we will fail. This is akin to treating diabetes with insulin or drugs alone, without any corresponding attempt to modify diet or weight.
Additional Concerns
- Secondary Gain: Disability payments, legal actions, and illicit financial incentives can complicate the treatment of pain. Practicing safe and appropriate medicine, with thorough documentation, will serve as a starting point, with specialty referral being necessary at times.
- Suicidality: Individuals whose lives have revolved around opioids for decades may have significant and legitimate concerns about dose reduction. These individuals need patience and behavioral support. Be sure to ask about suicidal thoughts and provide referrals to counseling when needed.
- Addiction (opioid-use disorder): It is sometimes hard to distinguish between patients who take opioids to relieve pain and those who are taking medication obsessively to relieve cravings or to achieve a pleasurable effect. Individuals who have an unnatural focus on their medications and respond poorly to opioid treatment may be identified as either having ineffectively treated pain or having an opioid-use disorder.
You may have patients to whom you were prescribing opioids for the treatment of pain, but who over time showed evidence of addiction. Ideally, if you prescribe opioids for chronic pain, you also have the capability to prescribe buprenorphine (or refer to others with that capability) for your patients who you feel have a substance-use disorder. Regardless of the terminology you use, some patients would be safer being prescribed buprenorphine rather than pure mu agonists.
An in-depth knowledge of your community addiction services is an important component of chronic pain treatment.
