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Electrophysiological Motor Unit Number Estimation MUNE Measuring Compound Muscle Action Potential CMAP in Mouse Hindlimb Muscles

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Published on: September 25, 2015

Assessment of motor unit loss in patients with spinal muscular atrophy

Boudewijn T H M Sleutjes¹, Camiel A Wijngaarde¹, Renske I Wadman¹

¹Department of Neurology, UMC Utrecht Brain Center, University Medical Center Utrecht, Utrecht University, the Netherlands.

Clinical Neurophysiology : Official Journal of the International Federation of Clinical Neurophysiology

|April 20, 2020

Abstract

Objective:

To assess motor unit (MU) changes in patients with spinal muscular atrophy (SMA) using compound muscle action potential (CMAP) scans.

Methods:

We performed CMAP scan recordings in median nerves of 24 treatment-naïve patients (median age 39; range 12-75 years) with SMA types 2-4. From each scan, we determined maximum CMAP amplitude (CMAP_max), a motor unit number estimate (MUNE), and D50 which quantifies the largest discontinuities within CMAP scans.

Results:

Median CMAP_max was 8.1 mV (range 0.9-14.6 mV), MUNE was 29 (range 6-131), and D50 was 25 (range 2-57). We found a reduced D50 (<25) in patients with normal CMAP_max (n = 12), indicating MU loss and enlarged MUs due to reinnervation. Lower D50 values were associated with decreased MUNE (P < 0.001, r = 0.68, n = 43). CMAP_max, MUNE and D50 values differed between SMA types (P < 0.001). Lower motor function scores were related to patients with lower CMAP_max, MUNE and D50 values (P < 0.001).

Conclusions:

The CMAP scan is an easily applicable technique that is superior to routine assessment of CMAP_max in SMA.

Significance:

The detection of pathological MU changes across the spectrum of SMA may provide important biomarkers for evaluating disease course and monitoring treatment efficacy.

Keywords:

CMAP scan Motor unit loss Spinal muscular atrophy Surface-EMG

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