Background : Chronic migraine (CM) is a disabling headache disorder. Autonomic nervous system (ANS) disturbance, as evidenced from heart rate variability (HRV) studies, has been documented in patients with episodic migraine and other pain disorders but not specifically in patients with CM. This study aimed to explore whether the HRV in patients with CM was impaired and whether it could be used to predict treatment outcomes.
Methods : Patients with CM were recruited, along with age- and gender-matched healthy controls (CTLs). The time-domain, frequency-domain, and nonlinear metrics of HRV were calculated to evaluate the sympathetic and parasympathetic aspects of ANS function in patients with CM before and after 3-month (12 weeks) treatment with flunarizine as well as in CTLs. The patients were asked to keep a headache diary throughout the study period to determine the treatment efficacy.
Results : A total of 81 patients with CM and 58 CTLs completed the study. Most HRV values in patients with CM were significantly lower than those in CTLs, suggesting decreased overall autonomic modulation and parasympathetic hypofunction but not sympathetic dysfunction. By unsupervised clustering analysis, patients with CM were divided into two cluster groups with high and low HRV at baseline. Patients with high baseline HRV, which was comparable to that of CTLs, showed significantly higher absolute and relative reductions in averaged monthly headache days across a 3-month preventive treatment compared with patients with low baseline HRV (-9.1 days vs. -6.4 days or -43.2% vs. -30.1%, both p < 0.05). The HRV increased after preventive treatment in the low-HRV group but not in the high-HRV group.
Conclusions : HRV could distinguish patients with CM from CTLs, indicating the involvement of ANS dysfunction. Moreover, patients with CM having a near-normal baseline HRV, indicating a preserved parasympathetic function and overall ANS modulation reservoir, predicted a better outcome to preventive treatment with flunarizine than those with low HRV.
Trial registration: Neurologic Signatures of Chronic Pain Disorders, NCT02747940.
Registered 22 April 2016, https://clinicaltrials.gov/ct2/show/NCT02747940