Higher Variability of Phosphene Thresholds in Migraineurs Than in Controls: A Consecutive Transcranial Magnetic Stimulation Study

Abstract

The aim of this study was to characterize the temporal course of phosphene thresholds (PT) using transcranial magnetic stimulation (TMS) in control subjects and in subjects with migraine and to observe whether changes in PT over time can predict a subsequent migraine attack. PTs were measured in 16 migraineurs [nine with aura (MA) and seven without aura (MoA)] and nine controls five times over an approximately 10-week period. Mean PTs were not significantly different between migraineurs and controls; however, there was a trend in MA showing lower thresholds. The minimum threshold values were also smaller in MA subjects than in MoA or control subjects. Generally, PTs had higher variance in migraineurs than in controls, revealing a significant increase in standard deviation of PTs in MA subjects. There was no significant difference of thresholds from the first to the last stimulation in controls and in MoA subjects, but the 3rd, 4th and 5th measurements of MA subjects were significantly lower than their first measurements. Four migraineurs experienced headache within 1 day after one of the measurements. They had either very low or very high PTs compared with the PT values which were not followed by a migraine attack. Our results imply that migraineurs show a higher variability among PT measurements over time than controls, revealing unstable excitability levels in these patients. Additionally, both particularly high and low PTs might predict a subsequent headache in some individuals.

Correlation between habituation of visual-evoked potentials and magnetophosphene thresholds in migraine: A case-control study

“…Finally, PTs in migraine patients were not different from those of normal participants. This finding was similar to that reported by several authors (23)(24)(25)(26) but at variance with several others (15,17,(19)(20)(21)(22), we found no significant decrease of PT in migraineurs.…”

“…By contrast, several authors reported opposite results (23)(24)(25)(26): lower phosphene prevalence in MA but no difference between controls and MO patients, and similar mean PT in individuals reporting phosphenes, which was confirmed in the present investigation. In a study measuring PT over a 10-week period, Antal et al (23) found no significant difference between migraineurs and HVs; however, they noticed a high variability of PT over time in migraine patients, favoring instability of cortical excitability instead of hyperexcitability.…”

“…Conversely, several other studies found no differences in PT between migraineurs and controls (23)(24)(25)(26).…”

Electrophysiological response patterns of primary sensory cortices in migraine

“…→ excitability of the visual cortex. This was confirmed in a recent study by Antal et al [95], who measured PT in different sessions over a long time period and found that controls showed PT stability over time, whereas there were great variations of PT values in migraine patients. This study suggests that more objective and reliable methods to assess cortical excitability are preferable.…”

Altered processing of sensory stimuli in patients with migraine

“…Thalamocortical dysrhythmia might also explain the phenomena observed in patients with migraine who are treated with transcranial neuromodulation techniquesfor instance, the increased variability of dynamic changes in excitability 135 or the paradoxical homeostatic cer ebral plasticity. [136][137][138] In a proof of concept study, the plastic cortical changes induced by rTMS were found to be inversely related to thalamocortical activation.…”