4.1.2 Numeric Rating Scale
The Numeric Rating Scale (NRS), first described by Downie and colleagues109, is a numeric version of the VAS that asks individuals to choose a number from zero to 10 (or 20 or 100) to communicate their pain severity, with zero representing “no pain” and the higher number representing the “worst pain imaginable”110. Much like the VAS, the NRS is broadly utilized in both clinical and research settings due to its simplicity, and is a unidimensional operationalization of pain. Notably, as it only accepts discrete numerical responses, the NRS offers a less detailed pain gradation in comparison to the VAS111. In short, while the NRS, due to its simplicity, has demonstrated ease of application in some studies112, its inherent limitations necessitate careful interpretation in persons with chronic pain and OUD.
Despite its widespread use, literature supporting the use of NRS for patients with comorbid OUD and chronic pain is sparse. Much like the VAS, the NRS relies on self-report, which must be appreciated in patients with OUD while also considering the potential for altered pain perception and tolerance due to neurobiological changes from long-term opioid use113. Opioid-induced hyperalgesia and the overlap between pain and withdrawal can also complicate assessment87.
In an example of using the NRS for assessing pain in patients with OUD, Latif and colleagues conducted a cross-sectional study to assess the prevalence and characteristics of chronic pain among 560 persons with OUD receiving buprenorphine or methadone therapy in Norway114. An 11-point NRS was used to assess pain intensity in addition to a survey that captured pain duration, onset, triggers, sites, persistence, radiation, migration, triggers and medication effects. Chronic pain was reported by 55% of patients, and those with higher NRS pain scores were more likely to describe their pain as constant, migrating, not improved with analgesics, and triggered by stress and exercise. The study supports evidence that chronic pain is highly prevalent in persons with OUD and that the NRS has been used to successfully measure the severity of their pain.