Motor unit number index (MUNIX): Principle, method, and findings in healthy subjects and in patients with motor neuron disease

CareFusion, Middleton, Wisconsin, USA.
Muscle & Nerve (Impact Factor: 2.28). 11/2010; 42(5):798-807. DOI: 10.1002/mus.21824
Source: PubMed


The motor unit number index (MUNIX) is a method for assessment of number and size (MUSIX) of motor units (MUs) using the compound muscle action potential (CMAP) and surface electromyographic interference pattern (SIP). This method was used to study the hypothenar muscle in 34 healthy subjects to define normal range, and to study reproducibility. Four healthy subjects and 13 patients with amyotrophic lateral sclerosis (ALS) were studied serially over a 1-year period. In healthy subjects, MUNIX showed good reproducibility. In serial studies, healthy subjects showed no change in the CMAP amplitude and MUNIX. ALS patients with minimal change in CMAP amplitude had a significant drop in MUNIX and increase in MUSIX, indicating MU loss compensated by reinnervation. When the CMAP changed significantly (>30%) in 1 year, the CMAP and MUNIX decreased in parallel. MUNIX would be useful to study MU loss in degenerative diseases of motor neurons. Muscle Nerve 42: 798-807, 2010.

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    • "An explanation for this could be that MUP size measured with HD-MUNE contained SMUPs of all thenar muscles, while in the creation of MUSIX only the SIPs of the APB were used. MUSIX was not correlated to the CMAP amplitude in both ALS patients and healthy controls, as also found previously (Nandedkar et al., 2010). "
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    ABSTRACT: To evaluate how the motor unit number index (MUNIX) is related to high-density motor unit number estimation (HD-MUNE) in healthy controls and patients with amyotrophic lateral sclerosis (ALS). Both MUNIX and HD-MUNE were performed on the thenar muscles in 18 ALS patients and 24 healthy controls. Patients were measured at baseline, within 2 weeks, and after 4 and 8 months. Clinical evaluation included Medical Research Council (MRC) scale and the ALS functional rating scale (ALSFRS). There was a significant positive correlation between MUNE and MUNIX values in ALS patients (r=0.49 at baseline; r=0.56 at 4 months; r=0.56 at 8 months, all p<0.05), but not in healthy controls. After 8 months, both MUNE and MUNIX values of the ALS patients decreased significantly more compared to MRC scale, ALS functional rating scale (ALSFRS) and compound muscle action potential (CMAP) (p<0.05). There was no significant difference in relative decline of MUNIX and HD-MUNE values. In ALS patients, MUNIX and HD-MUNE are significantly correlated. MUNIX has an almost equivalent potential in detecting motor neuron loss compared to HD-MUNE. MUNIX could serve as a reliable and sensitive marker for monitoring disease progression in ALS.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 02/2012; 123(8):1644-9. DOI:10.1016/j.clinph.2012.01.004 · 3.10 Impact Factor
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    • "In MUNIX analysis, it should be noted that very low amplitude voluntary surface EMG signals can give very high ICMUC values. To exclude this artifact, three criteria were imposed to accept an SIP epoch [18]: (1) SIP area > 20 mVms; (2) ICMUC < 100; and (3) SIP area/CMAP area > 1. "
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    ABSTRACT: Notch filtering is the most commonly used technique for suppression of power line and harmonic interference that often contaminate surface electromyogram (EMG) signals. Notch filters are routinely included in EMG recording instrumentation, and are used very often during clinical recording sessions. The objective of this study was to quantitatively assess the effects of notch filtering on electrically evoked myoelectric signals and on the related motor unit index measurements. The study was primarily based on an experimental comparison of M wave recordings and index estimates of motor unit number and size, with the notch filter function of the EMG machine (Sierra Wave EMG system, Cadwell Lab Inc, Kennewick, WA, USA) turned on and off, respectively. The comparison was implemented in the first dorsal interosseous (FDI) muscle from the dominant hand of 15 neurologically intact subjects and bilaterally in 15 hemiparetic stroke subjects. On average, for intact subjects, the maximum M wave amplitude and the motor unit number index (MUNIX) estimate were reduced by approximately 22% and 18%, respectively, with application of the built-in notch filter function in the EMG machine. This trend held true when examining the paretic and contralateral muscles of the stroke subjects. With the notch filter on vs. off, across stroke subjects, we observed a significant decrease in both maximum M wave amplitude and MUNIX values in the paretic muscles, as compared with the contralateral muscles. However, similar reduction ratios were obtained for both maximum M wave amplitude and MUNIX estimate. Across muscles of both intact and stroke subjects, it was observed that notch filtering does not have significant effects on motor unit size index (MUSIX) estimate. No significant difference was found in MUSIX values between the paretic and contralateral muscles of the stroke subjects. The notch filter function built in the EMG machine may significantly reduce the M wave amplitude and the MUNIX measurement. However, the notch filtering does not jeopardize the evaluation of the reduction ratio in maximum M wave amplitude and MUNIX estimate of the paretic muscles of stroke subjects when compared with the contralateral muscles.
    Journal of NeuroEngineering and Rehabilitation 11/2011; 8(1):64. DOI:10.1186/1743-0003-8-64 · 2.74 Impact Factor
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    • "Therefore , the MUNIX values in different muscles may not match the actual motor unit numbers estimated using various MUNE methods. As Nandedkar et al. have pointed out, in definition of the MUNIX measurement, the choice for 20 mV·ms SIP area is somewhat arbitrary [20]. The rationale for this selection is that such an SIP area is usually recorded at slight muscle contraction levels so most of the active motor units are small and should relatively have similar size. "
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    ABSTRACT: The objective of this study is to assess whether there is evidence of spinal motoneuron loss in paretic muscles of stroke survivors, using an index measurement called motor unit number index (MUNIX). MUNIX, a recently developed novel neurophysiological technique, provides an index proportional to the number of motor units in a muscle, but not necessarily an accurate absolute count. The MUNIX technique was applied to the first dorsal interosseous (FDI) muscle bilaterally in nine stroke subjects. The area and power of the maximum M-wave and the interference pattern electromyogram (EMG) at different contraction levels were used to calculate the MUNIX. A motor unit size index (MUSizelndex) was also calculated using maximum M-wave recording and the MUNIX values. We observed a significant decrease in both maximum M-wave amplitude and MUNIX values in the paretic FDI muscles, as compared with the contralateral muscles. Across all subjects, the maximum M-wave amplitude was 6.4 ± 2.3 mV for the paretic muscles and 9.7 ± 2.0 mV for the contralateral muscles (p <; 0.001). These measurements, in combination with voluntary EMG recordings, resulted in the MUNIX value of 109 ± 53 for the paretic muscles, much lower than the MUNIX value of 153 ± 38 for the contralateral muscles (p <; 0.01). No significant difference was found in MUSizelndex values between the paretic and contralateral muscles. However, the range of MUSizelndex values was slightly wider for paretic muscles (48.8-93.3 μV) than the contralateral muscles (51.7-84.4 μV). The findings from the index measurements provide further evidence of spinal motoneuron loss after a hemispheric brain lesion.
    IEEE Transactions on Information Technology in Biomedicine 08/2011; 15(4-15):505 - 512. DOI:10.1109/TITB.2011.2140379 · 2.49 Impact Factor
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