The Second Exteroceptive Suppression Period of the Temporalis Muscle Is Altered in Migraine Patients with Allodynia.

Background/Objectives: Studying the second exteroceptive suppression period (ES2) of the temporalis muscle may well shed some light on the brainstem neural circuits involved in migraine pathophysiology. It is known that allodynia is related to an increased sensitization of second-/third-order neurons both in the trigeminal nucleus caudalis and sensory thalamus. This pilot, observational study was carried out in the interictal period on female migraineurs with/without allodynia to assess the ES2 of the temporalis muscle compared to controls. Methods: Forty-nine non-consecutive female patients were enrolled, as they met the diagnostic criteria for migraine (26 episodic and 23 chronic), alongside 23 healthy controls. The inclusion criteria encompassed no ongoing pharmacological prophylactic treatment, and the exclusion criteria included any relevant comorbidities. In line with international standards, the exteroceptive suppression of the temporalis muscle activity was registered on the left side, assessing ES2 latency and duration in the interictal period. Results: Allodynia was observed in 24 patients (50%), and 16/24 (67%) were chronic migraineurs. No statistically significant differences in ES2 latency or its duration between the migraine patients and controls were detected. However, there was a significantly longer ES2 duration in allodynic migraineurs than in the controls (p = 0.04; effect size: 0.71) and in allodynic compared to non-allodynic migraineurs (p = 0.04; effect size: 0.63). Conclusions: The increased duration of ES2 observed in allodynic migraineurs might be related to the impaired activity of brainstem circuits and, in our opinion, it seems reasonable to hypothesize that this change may be a neurophysiological correlate of central sensitization in migraine allodynic patients.