Posterior Auricular Muscle Response: Observations in Brainstem Lesions

Objective: Posterior auricular muscle response (PAMR) is a myogenic potential recorded over PAM after auditory stimulation. Its circuit is formed by cochlear and facial nerves with the generator in the brainstem. Here, we investigated whether the addition of a PAMR examination would add additional use in determining or localizing isolated brainstem lesions given that the importance of blink reflex (BR) in determining or localizing brainstem lesions is known. Our hypothesis was that examination of both reflexes would increase clinical utility. Materials and Methods: We included 34 patients with isolated brainstem lesions (multiple sclerosis, ischemic stroke and cerebellopontine angle schwannoma) and 41 healthy subjects. PAMRs were recorded over the PAM after auditory stimulation. BR was elicited by the electrical stimulation of the supraorbital nerve. Results: PAMR was present in 82.9% of healthy subjects, whereas the presence was quite low in the patient group (38.2%, p=0.001). The mean latency of PAMR was delayed in patients compared with healthy subjects (p=0.001). BR was obtained in all healthy subjects, whereas prolonged latencies or absence of BR was observed in the patient group. There were no differences according to the different etiologies or localization. Conclusion: Although the presence of PAMR is quite high, its absence does not always indicate a pathology. However, prolonged latencies almost always suggest an involvement of the PAMR pathway. Likewise, absent PAMR with an abnormal BR provides information for the involvement of brainstem facial nucleus or the proximal part of the facial nerve