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.