Pain Medications – Are They Making Things Worse?
Pain is the most common cause of visits to the physician and millions of people suffer from daily pain, including neck pain and back pain. To treat such pain it is common to use NSAIDs, analgesics, and other conservative neck pain therapies before looking at more invasive options such as neck surgery or spine surgery. Many patients self-medicate, creating potential problems including liver dysfunction and emotional dependency on analgesics. Using analgesics to numb neck pain indefinitely also increases the likelihood of a problem becoming worse through repeated overuse and trauma of spinal structures. A correctable minor spinal issue can then progress unchecked to become a full-blown degenerative spine disease requiring surgery. Adding in this newly highlighted possibility of opioid-induced hyperalgesia (OIH) may make many more physicians think twice before prescribing pain medications long-term.
Opioid-Induced Hyperalgesia Not the Same as Tolerance
Opioid can be very helpful in pain management but chronic pain can continue even when such pain medications are used. The paradoxical notion that these very opiates could be worsening and prolonging neck pain is worrying but it appears that the phenomenon exists independently of tolerance, addiction, dependence, and the progression of any underlying spine disease. OIH is an increased nociceptive sensitization caused by opioid exposure. This is not the same as increased tolerance to opioids which is common and is one of the reasons these pain-relief drugs tend to be prescribed for short periods only. The incidence of OIH is unknown and could be a significant, and under-appreciated issue.
Do Opioids Make Neck Pain Worse?
Unlike increased opioid tolerance, opioid-induced hyperalgesia is thought to occur quickly and result in worse pain when a higher dose of opioids is given. Those who have developed an increased tolerance for opioids do so over time and will usually experience pain relief when their dosage is increased. OIH sufferers also appear to report higher pain levels than when first seeking medical attention, meaning that neck pain could actually feel worse after taking opioids and developing OIH.
Opioid-induced hyperalgesia may also be mistaken for undermedication for pain but this can usually be distinguished by pain relieving as more opioids are given, rather than becoming worse. Opioid withdrawal is also known to result in hyperalgesia (increased pain), which can make diagnosis of OIH even more confusing. Theoretically, ceasing the use of opioids in cases of opioid-induced hyperalgesia would resolve the pain but the effects of withdrawal could mask this improvement by increasing pain itself.
Sharp Localized Neck Pain vs. Diffuse Pain
Other ways that physicians, and patients, can detect opioid-induced hyperalgesia include symptoms such as pain from noxious stimuli, and pain that is less distinct and more diffuse. Sharp pain centered on specific parts of the neck or spine may, therefore, represent pain from undertreatment with analgesics, rather than a case of OIH. A more widespread pain extending outside the area of trauma or disease is more common in opioid-induced hyperalgesia. Pain may continue in OIH even after the original cause of the pain has been successfully treated. Patients undergoing neck surgery and taking opioids during their recovery may wish to watch for signs of OIH such as increased neck pain despite assertions by their surgeon that the structural defects has been resolved. Some cases of failed back surgery syndrome may even need revising in light of these new findings of OIH.
Causes of Opioid-Induced Hyperalgesia
It remains largely unknown as to what causes opioid-induced hyperalgesia although the leading theory is one of neuroexcitation. This model proposes that some opioids and the products created during their breakdown in the body have adverse effects on the N-methyl-D-aspartate (NMDA) receptor. This triggers an influx of calcium and subsequently enhances neuron’s excitability to a significant degree. This hyperactivation of the neurons means that pain signals are more readily transmitted when initiated by substance P, such as in fibromyalgia, or other stimulus.
Ketamine and OpioidsThis theory is supported by evidence that blocking NMDA receptors in cases of OIH successfully relieves the pain. One such drug to do this is ketamine as this prevents the influx of calcium that sensitizes the neurons. Patients taking codeine, hydromorphone, or morphine have different rates of glucuronidation or other pathways of metabolism of these opioids. Even the foods we eat can affect the breakdown and excretion of such drugs as these influence glucuronidation and other metabolic processes.
Worse Neck Pain May Not Mean Spinal Degeneration
Information on OIH in humans is scarce and animal models are still being used in an effort to understand the possible processes involved in this experience of worsened pain after treatment. In the meantime, strategies such as immediate cessation of opioid drugs mean that patients may be left with severe neck pain and other pain conditions and little choice regarding treatment. Some studies looking at the use of NMDA receptor antagonists are planned or underway and these may help elucidate the issue of opioid-induced hyperalgesia. Understanding which patients are more likely to develop OIH will then help focus clinical research on helping such sufferers. Sadly, those experiencing chronic neck pain and opioid-induced hyperalgesia may not realize that the reason for their worsening pain is not spinal degeneration but the very pain medications they take to treat it.