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Updated: Mar 16, 2026
EEG Mu Rhythm in Typical and Atypical Development
Published on: April 9, 2014
Unilateral Mu Rhythm and Associated Cortical Lesions on Brain MRI
Wissam R Yamak1, Ahmad A Beydoun, Maya M Dirani
1*Department of Neurology, American University of Beirut Medical Center, Beirut, Lebanon; †Division of Neurology, Labib Medical Center, Saida, Lebanon; and ‡Division of Neurology, Rafic Hariri University Hospital, Beirut, Lebanon.
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.
Insights
A unilateral mu rhythm on electroencephalogram (EEG) is rare, occurring in 0.05% of patients. This finding suggests searching for an ipsilateral brain lesion, even without other EEG abnormalities.
Area of Science:
- Neuroscience
- Epileptology
- Radiology
Background:
- The mu rhythm is a common EEG pattern observed over the sensorimotor cortex.
- Unilateral abnormalities in EEG can indicate underlying focal brain pathology.
Purpose of the Study:
- To determine the frequency of unilateral mu rhythm on scalp EEG.
- To investigate associated neuroimaging findings using dedicated epilepsy protocol brain MRI.
Main Methods:
- Retrospective review of EEG reports from 2011-2014 at a major medical center.
- Identification of patients with unilateral mu rhythm and analysis of their demographics, EEG data, and MRI findings.
Main Results:
- A unilateral mu rhythm was identified in 4 out of 7986 patients (0.05%).
- Three patients with unilateral mu rhythm were diagnosed with localization-related epilepsy.
- Brain MRIs revealed ipsilateral cortical lesions in the parietal lobe for the epilepsy patients.
Conclusions:
- Unilateral mu rhythm is a rare EEG phenomenon.
- Its presence warrants investigation for an ipsilateral brain lesion, particularly cortical lesions.
- This finding is significant even if other EEG abnormalities are absent.
