Reproducibility of MUNIX in patients with amyotrophic lateral sclerosis

Abstract

MUNIX has very good reproducibility in ALS patients. COV may exaggerate interoperator variation when MUNIX is very low. The higher variability in the thenar muscle is also due to variability in compound muscle action potential amplitude. Although both muscles show good reproducibility, the hypothenar is better suited for serial studies in individual patients.

Assessment of Motor Units in Neuromuscular Disease

“…There are some arbitrary criteria imposed to accept a SIP. A motor unit size index can be similarly obtained by dividing the total CMAP by the MUNIX [48,49].…”

Applicability of the digital instrument to improve the reproducibility of motor unit number index

“…The coefficient of variation (COV)s of MUNIX were 14.3 (APB) and 13.6 (ADM), and furthermore COVs of MUSIX were 12.7 (APB) and 14.1 (ADM), within the acceptable range for healthy subjects. [2][3][4][5][6] In addition, the correlation coefficients of MUNIX and MUSIX values measured by the different operators were significant by applying the digital instrument ( Table 1, Fig. 1).…”

“…Previous studies have reported high reproducibility of MUNIX in a few muscles including the APB, ADM, fist dorsal interossei (FDI), biceps brachii (BB), tibialis anterior (TA), abductor hallucis (AH), nasalis and orbicularis oculi (OO) muscles, in healthy subjects or in patients with ALS. [2][3][4][5][6] Practically, the MUNIX would be influenced by the variability of CMAP amplitude, and furthermore the MUNIX depends on the SIP recorded during voluntary muscle contraction, a critical element of all MUNIX techniques. Therefore, MUNIX can be limited by unreliable SIP signals, which may not reflect the state of the motor neuron with fidelity.…”

“…The MUNIX method involved assessing the APB and ADM muscles and the compound muscle action potential (CMAP) of the APB and ADM muscles were recorded using 10-mm flat disk electrodes with standard nerve conduction protocols stimulating median and ulnar nerve supramaximally, as has been previously reported. [1][2][3][4][5] The ADM and APB muscles were fully activated respectively by abduction of the little finger or by abduction of the thumb against a digital instrument calibrated by the manufacturer (Jamar Plus ® + Digital Hand Dynamometer, Sammons Preston Inc., Bolingbrook, IL, USA), and thereby the maximal muscle power could be digitally checked. Each muscle was gradually re-activated at five different levels of isometric force from minimum to maximum (slight, 25%, 50%, 75%, and 100%) using a digital instrument.…”

“…2,3 In conclusion, the mean values of MUNIX, the inter-operator COV (APB; 14.3, ADM; 13.6, Table 1), and the correlation coefficients (0.849 and 0.807, Table 1) indicate that the measurements after applying the digital dynamometer were much more reliable compared to those obtained in previous MUNIX and MUNE investigations. 2,3,[5][6][7][8][9][10][11] This technical improvement can be attributed to our efforts to reduce the test-retest variability while recording SIP signals by assuring close monitory through the digital dynamometer. In addition, our study revealed excellent test-retest reproducibility of MUSIX when assessing the average size of the motor units by using the digital instrument.…”