Primary visual cortex excitability in migraine: a systematic review with meta-analysis

The objective is to update and extend previous results of a systematic review of the literature with meta-analysis performed to determine the prevalence of phosphenes and the phosphene threshold (PT) values obtained during single-pulse transcranial magnetic stimulation (TMS) in adults with migraine. Both published and unpublished controlled studies measuring PT by single-pulse TMS in adults with migraine with or without aura (MA, MwA) were systematically reviewed. Prevalence of phosphenes and PT values were assessed calculating mean difference (MD) and odds ratio (OR) with 95 % confidence intervals (CI). Fifteen trials (369 migraine patients and 269 controls), were included. Patients with MA had a statistically significant lower PT compared with controls when a circular coil was used (MD: −22.27, 95 % CI −33.44 to −11.10); with a figure-of-eight coil the difference was not statistically significant. There was a significant higher phosphene prevalence in MA compared with controls (OR: 3.57, 95 % CI 1.16–10.94). No significant differences were found either in phosphene reporting between patients with MwA and controls, or in PT values obtained by figure-of-eight coil in subjects with MwA versus controls. In general, these results slightly support the hypothesis of a primary visual cortex hyper-excitability in MA, providing not enough evidence for MwA. A significant heterogeneity across studies probably reflects relevant clinical and methodological heterogeneity.