Background: Fibromyalgia (FMS) and high frequency episodic/chronic migraine (M) very frequently co-occur, suggesting common pathophysiological mechanisms; both conditions display generalized somatic hyperalgesia. In FMS-M comorbidity we assessed if: a different level of hyperalgesia is present compared to one condition only; hyperalgesia is a function of migraine frequency; migraine attacks trigger FMS symptoms.
Methods: Female patients with fibromyalgia (FMS)(n.40), high frequency episodic migraine (M1)(n.41), chronic migraine (M2)(n.40), FMS + M1 (n.42) and FMS + M2 (n.40) underwent recording of: -electrical pain thresholds in skin, subcutis and muscle and pressure pain thresholds in control sites, -pressure pain thresholds in tender points (TePs), -number of monthly migraine attacks and fibromyalgia flares (3-month diary). Migraine and FMS parameters were evaluated before and after migraine prophylaxis, or no prophylaxis, for 3 months with calcium-channel blockers, in two further FMS + H1 groups (n.49, n.39). 1-way ANOVA was applied to test trends among groups, Student's t-test for paired samples was used to compare pre and post-treatment values.
Results: The lowest electrical and pressure thresholds at all sites and tissues were found in FMS + M2, followed by FMS + H1, FMS, M2 and M1 (trend: p < 0.0001). FMS monthly flares were progressively higher in FMS, FMS + M1 and FMS + M2 (p < 0.0001); most flares (86-87 %) occurred within 12 h from a migraine attack in co-morbid patients (p < 0.0001). Effective migraine prophylaxis vs no prophylaxis also produced a significant improvement of FMS symptoms (decreased monthly flares, increased pain thresholds)(0.0001 < p < 0.003).
Conclusions: Co-morbidity between fibromyalgia and migraine involves heightened somatic hyperalgesia compared to one condition only. Increased migraine frequency - with shift towards chronicity - enhances both hyperalgesia and spontaneous FMS pain, which is reversed by effective migraine prophylaxis. These results suggest different levels of central sensitization in patients with migraine, fibromyalgia or both conditions and a role for migraine as a triggering factor for FMS.
Keywords: Central sensitization; Fibromyalgia; Hyperalgesia; Migraine; Pain thresholds; Tender points.