Comparison of numerical and verbal rating scales to measure pain exacerbations in patients with chronic cancer pain

Background: Numerical rating scales (NRS), and verbal rating scales (VRS) showed to be reliable and valid tools for subjective cancer pain measurement, but no one of them consistently proved to be superior to the other. Aim of the present study is to compare NRS and VRS performance in assessing breakthrough or episodic pain (BP-EP) exacerbations. Methods: In a cross sectional multicentre study carried out on a sample of 240 advanced cancer patients with pain, background pain and BP-EP intensity in the last 24 hours were measured using both a 6-point VRS and a 0-10 NRS. In order to evaluate the reproducibility of the two scales, a subsample of 60 patients was randomly selected and the questionnaire was administered for a second time three to four hours later. The proportion of "inconsistent" (background pain intensity higher than or equal to peak pain intensity) evaluations was calculated to compare the two scales capability in discriminating between background and peak pain intensity and Cohen's K was calculated to compare their reproducibility. Results: NRS revealed higher discriminatory capability than VRS in distinguishing between background and peak pain intensity with a lower proportion of patients giving inconsistent evaluations (14% vs. 25%). NRS also showed higher reproducibility when measuring pain exacerbations (Cohen's K of 0.86 for NRS vs. 0.53 for VRS) while the reproducibility of the two scales in evaluating background pain was similar (Cohen's K of 0.80 vs. 0.77). Conclusions: Our results suggest that, in the measurement of cancer pain exacerbations, patients use NRS more appropriately than VRS and as such NRS should be preferred to VRS in this patient's population.