Side-to-side differences in pressure pain thresholds and pericranial muscle tenderness in strictly unilateral migraine

Previous studies dealing with pressure pain sensitivity or muscle tenderness in migraine have shown conflicting results. Our aim was to explore the differences in mechanical pain sensitivity and pericranial muscle tenderness between patients with unilateral migraine and healthy controls, and to analyse side-to-side differences in both study groups. Pressure pain thresholds (PPT) at cephalic and neck points, plus local and total tenderness scores were blindly assessed in 25 patients with strictly unilateral migraine and 25 healthy subjects. For PPT in the neck there were significant differences between groups (F = 47.029; P < 0.001) and sides (F = 6.363; P < 0.01), and a significant interaction between group and side (F = 5.201; P = 0.02), while PPT in the cephalic point showed differences between groups (F = 11.774; P < 0.001), but not sides (F = 2.838; P = 0.1). The total tenderness score showed significant differences between groups (F = 6.800; P < 0.01) and sides (F = 17.699; P < 0.001), along with a significant interaction between group and side (F = 14.420; P < 0.001). Patients had lower PPT and increased pericranial tenderness on the symptomatic side as compared with the non-symptomatic side and to either side in controls (P < 0.001), whereas no significant differences were identified between the non-symptomatic side and controls (P > 0.9). In migraine patients, PPT levels and muscle tenderness scores were negatively correlated (P < 0.001). The enhancement of local tenderness scores was related to hyperesthesia of specific muscles (sternocleidomastoid, suboccipital, and temporalis) rather than a generalized pericranial tenderness. Future studies should investigate the neuro-physiological basis for the laterality of allodynic and hyperalgesic responses in unilateral migraine.