Cortical inhibition is reduced in chronic and episodic migraine and demonstrates a spectrum of illness.

BACKGROUND The pathophysiological relationship between episodic migraine and chronic migraine is not fully understood. We aimed to examine transcranial magnetic stimulation (TMS) indices of cortical excitability in patients with episodic migraine (EM) and probable chronic migraine (PCM), and matched controls. METHODS Cortical excitability was assessed at baseline with two well-established methods: phosphene thresholds (PT) and magnetic suppression of perceptual accuracy (MSPA) profiles. Five EM patients, five PCM patients, and five normal controls participated in the main study. In addition, two patients were reassessed after 30 days of treatment with topiramate. RESULTS Both PT and MPSA measures were consistent in indicating a continuum of excitability across the three groups: PCM patients had the highest excitability, followed by EM, then controls. In the two treated patients MPSA profiles appeared to normalize at a 100 mg dosage. CONCLUSIONS Patients with PCM appear to be characterized by very high cortical excitability. This may contribute to their greatly increased attack frequency. TMS-based methods will be important for future research examining the evolution of chronic migraine from episodic migraine over time.