Effects of Divalproex sodium for Visual Cortex Excitability in Migraine: A Study Using Transcranial Magnetic Stimulation

ABSTRACT

BACKGROUND: The pathophysiology of migraine has not been fully understood. One of the hypotheses is cortical hyperexcitability. Transcranial magnetic stimulation (TMS) is a noninvasive electrophysiologic tool for the investigation of cortical excitability. Divalproex sodium may prevent migraine attacks by increasing the GABA-ergic tone. We examined the phosphene generation using TMS in migraine patients in order to investigate the cortical excitability and its response by valproate prophylaxis. METHODS: We applied TMS to 27 migraineurs and 27 control subjects. TMS was performed by a Magstim Rapid Stimulator connected to a 70 mm figure-of-eight coil to examine the phosphene threshold between migraineurs and controls on primary (V1) and bilateral secondary (V5) visual cortices. Twelve migraine patients completed a one month administration of divalproex sodium 500 mg/day. We compared the phosphene threshold between pre- and post-treatment with devalproex sodium in these patients. RESULTS: The prevalence of the phosphene generation was significantly higher in migraineurs compared with controls in V1 and V5. The phosphene average thresholds were significantly lower in migraineurs compared with controls in V1 and V5. The phosphene average thresholds in the same areas were significantly higher in post-treatment compared with pre-treatment in migraineurs. CONCLUSIONS: The differences of the phosphene threshold in the visual cortex between migraineurs and controls comply with the theory of cortical hyperexcitability for the pathophysiology of migraine. Valproate might play a significant role in the prophylaxis of migraine by decreasing cortical hyperexcitability.