Get access

Far-field potentials in hypothenar motor unit number estimation


  • This study was supported by grants-in-aid for scientific research (19591011 and 23591285) from the Ministry of Education, Science, Sports and Culture of Japan, and by Health and Labor Sciences Research Grants for research on intractable diseases (CNS Degenerative Disease Research Committee and Neuroimmunological Disease Research Committee) from the Ministry of Health, Labour and Welfare of Japan.

Correspondence to: M. Sonoo; e-mail:


Introduction: Contamination by far-field potentials (FFPs) may interfere with motor unit number estimation (MUNE) in the ulnar nerve. Methods: Surface motor unit potentials (SMUPs) from 29 spinal and bulbar muscular atrophy (SBMA) patients and 27 control subjects were classified into SMUPs from the abductor digiti minimi muscle (ADM SMUPs) or non-ADM SMUPs, based on the waveform patterns from 3-channel recordings. Results: The mean areas of the ADM SMUPs and non-ADM SMUPs in control subjects were 219.0 ± 131.3 and 63.7 ± 48.5 μVms, respectively. In SBMA patients they were 1988.9 ± 999.4 and 222.7 ± 125.7 μVms, respectively. The percentages of non-ADM SMUPs were 68 ± 22% in controls and 84 ± 15% in SBMA patients. Conclusions: Non-ADM SMUPs generated mainly by FFPs often had a negative onset in the routine lead and were indistinguishable from ADM SMUPs. More frequent exclusion of smaller non-ADM SMUPs in controls by size criteria would reduce the diagnostic yield of MUNE. Muscle Nerve, 48: 191–197, 2013