Migraine patients experience heightened resting cranial and proximal cervical muscle activity, according to a new study published in Clinical Neurophysiology.
Beginning in the 1970s, several researchers have looked at the role of muscle in migraine headaches, as well as tension headaches. Most of these studies have been qualitative and have demonstrated mixed results. Nevertheless, many of these studies have suggested a link between muscle activation and migraine.
“The International Classification of Headache Disorders (ICHD) considers muscle to be relevant in tension-type headache, but does not address its relevance in migraine,” wrote authors of the new study, led by John O. Willoughby, MBBS, PhD, emeritus professor, Centre for Neuroscience, College of Medicine and Public Health, Flinders University, Adelaide, Australia.
Quantitative studies of muscle activity have usually focused on tension headaches, with migraines serving as comparison. These studies have also yielded mixed results, and involved different methods of muscle activity quantitation, making the drawing of either comparisons or conclusions difficult.
In the current topographic quantitative study, researchers used whole-head high-density scalp electrical recordings, independent component analysis (ICA), and spectral slope of the derived components to establish electromyogram-containing components representing muscle activity. The team quantified scalp spectral power representing muscle activation in the range of 52-98 Hz. Notably, advances in signal analysis have allowed experts to extract electromyogram (EMG) activity from scalp electrical recordings.
The researchers mined data used in the current study from an extant dataset obtained from a wide gamut of patients with neurological and psychiatric disorders and from controls. The purpose of this dataset was to probe changes in brain rhythms associated with different conditions. The team analyzed data from 65 healthy controls and 26 migraine patients.
Migraine patients exhibited more spectral power secondary to migraine (-13.61 dB) than did controls (-14.73 dB; P=0.028). Furthermore, more power was observed in the eye-open vs eyes-closed state (-13.42 vs -14.9 dB, respectively; P=0.001). On linear regression, the team observed no association between headache prevalence and muscle activity as accorded by any combination of region or task.
“The differences between this and previous studies are that our migraine participants were not selected for severity and, therefore, mostly had a frequency of headache less than two per month, and that they were recorded in their non-headache phase,” the authors wrote. “These differences strengthen the finding because it is not confounded either by the complicating intra-individual reactions to acute headache pain, nor to the selection of an atypical sub-group of migraineurs.”
Because researchers did not assess the timing of subsequent migraines, they conceded that some patients could have been pre-ictal at analysis. These pre-ictal cases could bias study results, although this unlikely due to the infrequency of migraine in many subjects, as well as the absence of a relationship between muscle activity and migraine frequency.
“Our study does not address muscle activity during an acute headache but, given others’ work, it would be surprising to find a reduced level during headache than that recorded in the headache-free period,” the authors wrote.
Dr. Willoughby and colleagues suggested that their findings of heightened muscle activity could be a clinical marker of migraine.
Of interest, the team found that men and women experienced no difference in resting muscle activity—whether or not experiencing migraines—despite the frequency of migraine being higher in women and more women taking botulinum toxin for relief of migraine symptoms.
“There is an increase in cranial and upper cervical muscle activity in non-ictal migraineurs versus controls,” concluded the authors. “This raises questions of the role of muscle in migraine, and the possible differentiation of non-ictal phases.”
This work was supported by the National Health and Medical Research Council, the Flinders Medical Centre Foundation, the Clinician’s Special Purpose Fund of the Flinders Medical Centre, and an equipment grant from the Wellcome Trust, London, UK.