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γ-Aminobutyric acid (GABA) has been implicated in several pain conditions, yet no study has systematically evaluated GABA levels in migraine using (1) H-MRS. The accurate detection, separation and quantification of GABA in individuals with migraine could elucidate the role of this neurotransmitter in migraine pathophysiology. Such information may eventually be useful in the diagnosis and development of more effective treatments for migraine. The aims of this study were therefore to compare the concentration of GABA+ in individuals with migraine with that in asymptomatic individuals, and to determine the diagnostic potential of GABA+ in the classification of those with or without migraine. In this case-control study, GABA+ levels in the brain were determined in 19 participants with migraine and 19 matched controls by (1) H-MRS using Mescher-Garwood point-resolved spectroscopy (MEGA-PRESS) sequence. The diagnostic accuracy of GABA+ for the detection of migraine and the optimal cut-off value were determined by receiver operating characteristic analysis. GABA+ levels were significantly higher (p = 0.002) in those with migraine [median, 1.41 institutional units (IU); interquartile range, 1.31-1.50 IU] than in controls (median, 1.18 IU; interquartile range, 1.12-1.35 IU). The GABA+ concentration appears to have good accuracy for the classification of individuals with or without migraine [area under the curve (95% confidence interval), 0.837 (0.71-0.96); p < 0.001]. The optimal GABA+ cut-off value for migraine was 1.30 IU, with a sensitivity of 84.2%, specificity of 68.4% and positive likelihood ratio of +2.67. The outcomes of this study suggest altered GABA metabolism in migraine. These results add to the scarce evidence on the putative role of GABA in migraine and provide a basis to further explore the causal relationship between GABA+ and the pathophysiology of migraine. This study also demonstrates that GABA+ concentration has good diagnostic accuracy for migraine. These findings offer new research and practice directions for migraine diagnosis.

Background Clear definitions of study populations in clinical trials may facilitate application of evidence to clinical populations. This review aimed to explore definitions of study populations in clinical trials on migraine, tension-type headache, cluster headache, and cervicogenic headache. Methods We performed a systematic review of clinical trials investigating treatment efficacy for migraine, tension-type headache, cluster headache, and cervicogenic headache. We extracted data on diagnosis, inclusion criteria and baseline headache characteristics. Results Of the 229 studies reviewed, 205 studies (89.5%) defined their populations in adherence to the International Classification of Headache Disorders (ICHD) criteria. Some studies ( n = 127, 55.5%) specified diagnosing through interview, clinical examination and diary entry. The most commonly reported inclusion criteria were pain intensity for migraine and tension-type headache studies ( n = 123, 66.1% and n = 21, 67.7%, respectively), episode frequency ( n = 5, 71.4%) for cluster headache studies, and neck-related pain for cervicogenic headache studies ( n = 3, 60%). Few studies reported details on the extent to which diagnostic criteria were present at baseline. Conclusions ICHD is routinely used in defining populations in headache studies. Details of baseline headache characteristics were not as consistently reported.