What is chronic pain and why does it occur?
Chronic pain, generally described as pain lasting for more than 3 months, is one of the leading causes of disability in Europe and around the world. In Spain alone, the Spanish Society of Neurology (SEN) estimates that 32% of the population suffers from some type of pain and 11% of these suffer from chronic pain. The physical and mental distress this causes in a person’s day to day life inevitably has a serious negative impact on their quality of life.
There are many types of chronic pain. According to the World Health Organization (WHO), it can be classified into seven categories:
1. Primary chronic pain, which includes functional or psychological alterations of multifactorial origin, not caused by any underlying disease.
2. Chronic cancer pain, which as its name suggests is caused by the disease and its respective treatment.
3. Chronic post-surgical or post-traumatic pain, pain from injury or surgical procedures that persists after the healing period.
4. Chronic neuropathic pain, caused by a lesion or disease of the nervous system.
5. Chronic orofacial pain and headache, caused by lesions of the mouth and/or face and by headache.
6. Chronic visceral pain, internal organ pain.
7. Chronic musculoskeletal pain, arising from the bones, joints, muscles, spine, tendons, or soft tissue.
Although these classifications help distinguish certain types of pain, it is important to know that they are not exclusive categories, that is, there may be a diagnosis that fits into several categories. One of the biggest difficulties with chronic pain, however, is the path to this diagnosis, since doctors are often unable to detect a specific cause of the pain. This can lead to an arduous process both physically and mentally, during which the patient very often feels invalidated and stigmatized. Fortunately, during the last decades, the study of pain has increased significantly, with professionals who are better trained and informed about complications in etiology and detection.
Additionally, although treatment for chronic pain has improved a lot in the last years, it is still an extremely complex area. Certain conditions can be improved by simple anti-inflammatories such as ibuprofen (neck injuries, sprains, etc.). However, these drugs have a ceiling effect, that is, a limit to how much pain they can control. For more severe pain, opioids are also prescribed, but the risk of addiction and adverse effects is much higher with these types of medications. Among the most commonly prescribed medications for chronic pain are antidepressants, such as SSRIs and others. It is important to point out the use of antidepressants here, since many see pain as something purely physical. The evidence, however, points to a much more complex concept of pain, with a great impact of psychological and social factors. This implies that pain management needs a multidisciplinary approach, combining interventions which include exercise and physical therapy, drugs, diet, and psychological therapy.
In recent years, an exponential number of studies have been published on the use of ketamine for the treatment of chronic pain. Due to its use in medicine as a general anesthetic, it is a drug for which there is ample evidence of its safe use, as well as having a lower addictive risk than other drugs such as opioids. Its possible side effects are also minimal and do not usually last, with nausea and vomiting being the most commonly seen, as is the case with the use of ketamine for depression.
The evidence
There are many publications on the use of ketamine for chronic pain. A study published in 2019 by Orhuru and colleagues conducted a systematic review and meta-analysis of studies investigating the efficacy of intravenous ketamine in reducing chronic pain, compared to placebo. These studies included a wide variety of pain etiologies, such as neuropathic pain, cancer pain, and nociceptive pain (caused by external or internal injury). They included a total of seven studies in which patients suffered from moderate to severe pain. They found that there was a significant reduction in pain up to 4 weeks after the initial treatment. This reduction was found equally in all types of pain studied.
Another study by Zhao and colleagues (2018) investigated the impact of ketamine in the treatment of complex regional pain syndrome. This is a poorly understood syndrome that often occurs after injury or surgery, causing chronic pain out of proportion to the injury. In this meta-analysis, the researchers found a significant reduction in pain that was maintained up to 3 months after the initial treatment. These results show great promise for the future of chronic pain treatment, and reveal a great potential for ketamine to treat several types of pain.
As we have mentioned before, the best way to deal with chronic pain is through a multidisciplinary approach. Ketamine offers a significant and vital relief that, through the reduction of the pain symptomatology, allows the patients to make use of therapeutic techniques such as mindfulness and deep breathing. Nowadays, the use of technology has also opened many new lines of research. Virtual reality has already been used in many centers to offer treatments, such as meditation and psychoeducation. In dealing with a problem so debilitating as is chronic pain, it is absolutely necessary to keep on studying and researching to make advances in the field and to offer treatments that are more efficient and personalized.
