Migraine-linked characteristics of transcranial magnetic stimulation-induced phosphenes

Transcranial magnetic stimulation is used to explore visual cortex hyperexcitability in migraine. We hypothesized that the phosphene threshold in subjects suffering from migraines with and without aura would be lower than in controls, and this phenomenon could be linked to higher pain and disability levels. We also implied that subjects with lower phosphene threshold could see more phosphenes of different colors and shapes. Our primary objective was to compare the phosphene threshold between migraine without aura, migraine with aura, and control groups and investigate which factors contribute to different phosphene parameters in migraineurs. Secondary objectives were to compare color, shape, and number of phosphenes between groups and assess pain and disability level correlation with the phosphene characteristics. Phosphene threshold in migraine without aura, migraine with aura, and control groups were 68 +/- 9.5% vs. 75 +/- 12%, vs. 80 +/- 11%, respectively. Other phosphene parameters (number, color and shape) did not differ between groups. Average pain level during the attack did not correlate with phosphene threshold significantly, though the non-significant trend for negative correlation of migraine disability assessment scale score and a phosphene threshold has been found the higher was migraine disability assessment scale value, the lower was phosphene threshold (beta = -0.255; P = 0.139). Other variables: gender, age, migraine subtype, migraine duration and use of hormone contraceptives - were not related to the phosphene threshold value. Our study provides additional data on visual cortex hyperexcitability in migraineurs, regarding transcranial magnetic stimulation with a figure-of-eight coil. Visual cortex excitability might be linked to higher disability.