Reproducibility of motor unit number estimation in individual subjects.
Although the reproducibility of motor unit number estimation (MUNE) for groups of subjects has been studied, there is little such data for individuals. Prediction intervals represent a tool to study individual MUNE reproducibility and represent the range of values expected for a future MUNE if the true number of motor units remains unchanged. MUNE was performed using the statistical method on 48 normal individuals. The prediction interval was found to be a function of the intrasubject coefficient of variation. Using a commercial manufacturer's recommended technique and software, prediction intervals were found to be so broad as to be of uncertain value. We found that by averaging two MUNE observations for each determination, and using the method of weighted averages for calculating the size of an average single motor unit potential, the intrasubject coefficient of variation was reduced from 16.48% to 8.77%, and the 90% prediction interval became sufficiently narrow to be clinically useful. False-negative rates were also lowered substantially using these techniques. Thus, simple modifications of an existing MUNE program improved the clinical utility of this program for the longitudinal study of patients in whom changes in motor unit number over time are of importance, such as those with motor neuron diseases.
Division of Neurology, Pennsylvania State University College of Medicine, Hershey Medical Center, 500 University Drive, Hershey, Pennsylvania 17033-0850, USA. zsimmons@psu.edu
Z
Z
Simmons
D K
DK
Epstein
B
B
Borg
D T
DT
Mauger
M J
MJ
Kothari
J M
JM
Shefner
D000293:Adolescent; D000328:Adult; D000368:Aged; D004576:Electromyography / Q000379:methods*; D004594:Electrophysiology; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005188:False Negative Reactions; D005189:False Positive Reactions; D006801:Humans; D008875:Middle Aged; D008954:Models, Biological; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*; D011237:Predictive Value of Tests; D012016:Reference Values; D015203:Reproducibility of Results