Upper cervical two-point discrimination thresholds in migraine patients and headache-free controls

Background: Chronic pain including migraine is associated with structural and functional changes in the somatosensory cortex. Previous reports proposed two-point discrimination (TPD) as a measurement for cortical alterations. Limited evidence exists for tactile acuity in the neck and no data is available for migraine. Methods: To introduce a standardized protocol for the measurement of TPD in the upper cervical spine, 51 healthy participants were investigated with a newly developed paradigm which was evaluated for intra-rater reliability. The same protocol was applied by two further examiners to 28 migraine patients and 21 age-, and gender-matched healthy controls to investigate inter-rater reliability and between group differences. Results: Results indicated excellent intra-rater (right ICC(2,4) = 0.82, left ICC(2,4) = 0.83) and good inter-rater reliability (right ICC(2,4) = 0.70, left ICC(2,4) = 0.75). Migraine patients had larger TPD thresholds (26.86 +/- 7.21) than healthy controls (23.30 +/- 6.17) but these became only statistically significant for the right side of the neck (p = 0.02). There was a significant, moderate association with age for the right side (r = 0.42 p = 0.002, n = 51), and less strong association for the left side (r = 0.34, p = 0.14) in healthy individuals. TPD did not correlate with headache days per month or the dominant headache side in migraine patients. Conclusions: Surprisingly, migraine patients showed increased TPD thresholds in the upper cervical spine interictally. Although a body of evidence supports that hypersensitivity is part of the migraine attack, the current report indicates that interictally, migraine patients showed worse tactile acuity similar to other chronic pain populations. This has been hypothesized to indicate structural and functional re-organisation of the somatosensory cortex.