Reproducibility of pressure pain threshold and visual analog scale findings in chronic whiplash patients

BACKGROUND: Assessment of pain in patients with whiplash-associated disorders has been previously reported using a variety of instruments. However, the reproducibility of the findings derived from such measurements has not been explored with respect to this particular patients group. OBJECTIVES: To evaluate the intratester and intertester reproducibility of pressure pain threshold (PPT) findings and the intratester reproducibility of visual analog scale (VAS) findings relating to the cervical region of chronic whiplash patients for the determination of smallest real difference values. METHODS: Twenty-one chronic whiplash patients: 13 women and 8 men participated in this study. The intratester paradigm was based on 2 testing sessions over a period of 5 to 11 days (7.95±1.90) and incorporated recording of VAS scores and also PPT scores relating to 3 pairs of right and left homologous cervical sites. The intertester study was conducted within the first testing session and referred to the PPT measurement only. In this session, patients were also asked to fill in the Neck Disability Index questionnaire. RESULTS: The interclass correlation coefficient-derived reproducibility of the PPT scores was good to excellent within and between testers ranging 0.85 to 0.91 and 0.88 to 0.97, respectively. There was, however, a significant difference between the testers. The VAS scores demonstrated lower reproducibility (interclass correlation coefficient=0.67). On the basis of the standard error of measurement, the smallest real difference of PPT ranged 40.2 to 58.9 kPa whereas the corresponding figure for the VAS was 3.76 cm. CONCLUSIONS: On the basis of the current patient sample, this study demonstrates that although PPT findings may generally be applied for monitoring change in chronic whiplash patients, the use of VAS scores should be limited to patients whose initial score is above 4. It is also suggested that if the PPT is to serve as an outcome measure, its measurement should be performed by the same tester.