Unilateral Mu Rhythm and Associated Cortical Lesions on Brain MRI

Purpose:The purpose of this study was to assess the frequency of occurrence of a unilateral mu rhythm and the associated neuroimaging findings on dedicated epilepsy protocol brain MRI.Methods:We retrospectively reviewed the EEG reports database at the American University of Beirut Medical Center between 2011 and 2014 searching for the presence of a unilateral mu rhythm. For patients with a unilateral mu rhythm, we recorded the patients' demographics, number of EEGs performed, characteristics of the mu activity, and the findings on the epilepsy protocol brain MRIs.Results:A total of 7986 patients underwent 9,509 EEG between 2011 and 2014. Four patients (0.05%) aged between 19 and 55 years had evidence of a unilateral mu rhythm. Three patients were diagnosed with localization-related epilepsy and one with syncope. The brain MRIs showed cortical lesions involving the parietal cortex, ipsilateral to the unilateral mu rhythm in the three patients with epilepsy.Conclusions:A unilateral mu rhythm is a rare phenomenon on the scalp EEG that should prompt a search for an ipsilateral lesion, even in the absence of additional EEG abnormalities.