Objective: To assess the usefulness of repeat anal sphincter EMG for prognostication of MSA
Background: External anal sphincter (EAS) electromyography (EMG) is an established method for detecting neurogenic change of motor unit potentials (MUP), which reflects pathology of the Onuf’s nucleus. The value of EAS-EMG in the differential diagnosis of parkinsonism and diagnosis of MSA has been debated. In recent times, quantification of EMG abnormalities using a standard score and understanding of the associated features has allowed wider clinical application of EAS-EMG. Diagnostic yield improves with longer duration of symptoms, but there is no clear evidence that changes in EAS-EMG can progress over time or correlate with clinical course. The duration, areas and turns are variably used in the literature with no clear standardisation protocol.
Method: EAS-EMG was conducted at the Uroneurology department at Queen Square, London based on clinical indication. A standard concentric EMG needle – 26G/30G was used to examine the subcutaneous EAS muscle. A minimum of 20 MUPs were sampled using auto multi-MUP technique. All patients had clinical assessment of MSA using standardised scores and questionnaires. Data of EAS-EMG in the patients referred with a diagnosis of MSA to evaluate if progression of quantified scores were correlated with clinical progression.
Results: Of the 109 patients who had the EAS-EMG between January 2020 and February 2025, six (5.5%)had a repeat study based on clinical indications. Five (83.3%) patients showed abnormal results on first and second study. Four showed progression of EMG abnormalities that correlated with clinical deterioration over 1-2 years. One(16.7%) had a normal first and second study and had initially been diagnosed as Parkinson’s disease, that progressed to have autonomic and speech impairment after 10 years.
Conclusion: Abnormalities in EAS EMG can progress with time, and a follow up study especially in borderline cases can help improve the diagnosis. Progressive EAS EMG abnormalities can be explored as a potential biomarker for progression in early and prodromal MSA.
To cite this abstract in AMA style:
L. Lei, J. Bermejillo, P. Malladi, J. Panicker, A. Batla. Anal Sphincter EMG changes can Progress over Time and can be considered as a Prognostic Marker in MSA [abstract]. Mov Disord. 2025; 40 (suppl 1). https://www.mdsabstracts.org/abstract/anal-sphincter-emg-changes-can-progress-over-time-and-can-be-considered-as-a-prognostic-marker-in-msa/. Accessed October 5, 2025.« Back to 2025 International Congress
MDS Abstracts - https://www.mdsabstracts.org/abstract/anal-sphincter-emg-changes-can-progress-over-time-and-can-be-considered-as-a-prognostic-marker-in-msa/