Cortical silent period in facial muscles of patients with medication overuse headache

Objectives: We intend to study motor cortical inhibition in chronic daily headache with medication overuse headache (MOH) patients, and compared them with a group of healthy volunteers (HV) and migraine patients recorded interictally (MO). Background: Recently, in a transcranial magnetic stimulation (TMS) study we showed that episodic migraneurs with and without aura have shortened silent period (SP) in perioral muscles, as a result of reduced activation of Gaba-B ergic circuits in the motor cortex. This finding observed during the interictal phase has been interpreted as the motor counterpart of the reduced preactivation excitability level in the sensory cortices purported to explain why cortical evoked responses habituate poorly in patients with migraine. A percentage of migraine patients experience clinical evolution from initial episodic to chronic daily headache with medication overuse, which give us the opportunity to assess cortical excitability during a condition of persistent ictal phase. Methods: We recorded SP from perioral muscle by means of TMS in 15 MOH patients and 12 migraine without aura patients recorded interictally, and we compared them with 13 HV. Silent period was induced using a figure of eight TMS coil centered over the hot-spot for perioral muscles that delivered high intensity magnetic stimuli during a maximal muscle contraction. Electromyographic responses were recorded from surface electrodes placed over the subjects’ perioral muscles bilaterally. Results: Mean SP duration in MOH patients was similar to that of HV (respectively 107.12 ± 48.82 and 108.11 ± 30.11), while in MO patients interictally was significantly shortened. (59.99 ± 30.44; P = 0.009). In MOH patients SP duration correlated positively with monthly tablets intake (r = 0.679, P = 0.005). Conclusions: These findings provide neurophysiological evidence showing that excessive medication overconsumption induces normalization of the cortical motor inhibitory neurons underactivation found in episodic migraine interictally.