Relation Between the Severity of Liver Cirrhosis and Neurological Symptoms, Nerve Conduction Study Results, and Motor Unit Number Estimation

Reem M Gabr; Dina A El Salmawy; Mye A Basheer; Marwa khairy; Saly H Elkholy

Disclosures

J Viral Hepat. 2021;28(9):1312-1318. 

In This Article

Materials and Methods

This case-control study was performed during the period from August 2018 to December 2019. The study participants were divided into two groups: Group 1 included 56 patients diagnosed with liver cirrhosis. The MUNE values were compared to that of group 2, which was composed of 61 age- and sex-matched healthy volunteers.

The Group 1 patients were subdivided according to the presence of neurological symptoms (numbness, muscle cramps and/or fatigue) into Group 1A (symptom-manifesting group) and Group 1B (symptom-free group). Patients with compensated or decompensated cirrhosis were included in the study.

Patients with an identifiable comorbidities that can be a contributing cause of peripheral polyneuropathy (eg diabetes), patients who developed hepatocellular carcinoma or other chronic illnesses such as renal disease were excluded from the study to avoid other causes of metabolic neuropathies. None of our patients was known to be alcoholic or had signs suggestive of vitamin B12 deficiency.

Written informed consent was obtained from each patient. The research ethics committee of the Faculty of Medicine-Cairo University (MS-88 2019) approved the trial before the start of data collection and clinical trial registration (NCT04340999). The study protocol conformed to the ethical guidelines of the 1975 Declaration of Helsinki and its later amendments (as revised in Seoul, Korea, October 2008) with good clinical practice guidelines as reflected in a prior approval by the institution's human research committee. With respect to the patients' confidentiality, patients were represented in the study by code numbers and all personal data were concealed.

All participants in the study were clinically assessed for the presence of neurological symptoms and signs. The laboratory tests performed included complete blood count, liver function, kidney function, serum albumin, glycosylated haemoglobin and coagulation profile. A pelvic-abdominal ultrasound was also done. The liver cirrhosis severity was assessed by both the Child-Pugh classification and the Model for End-Stage Liver Disease (MELD) scoring system.[12]

Fatigue (or subjective fatigue) has been asked as 'an overwhelming sense of tiredness, lack of energy and feeling of exhaustion' that is 'not relieved by rest' that affect their daily activities,[13–15] while muscle Cramps was asked by the presence of severe pain, occurred in calf muscles several times a week (mainly at rest or during sleep) and lasted for a few minutes.[16]

To reply the study aim, modern, as well as classic, electrophysiologic studies were performed using the Natus Viking EMG machine 672–003800 REV.08 USA.

Motor unit is the fundamental functional unit of our movement, which acts as a transducer that converts neural signals into mechanical outputs by the muscle unit. Motor neurons can be divided into 3 groups: alpha, beta and gamma, according to the muscle fibre type they innervate.[17]

Motor unit potentials (MUPs) can be quantitatively described by several parameters; amplitude, area, duration, rise time, satellite potentials, phase, turns and complexity. Most of those parameters which are currently considered pertinent for assessment of motor unit characteristics can be quantified automatically.[18]

Quantitative analysis is a technique which is relatively old, beginning with the work of Buchthal and colleagues in the late 1940s.[19] It includes MUP waveform measurements, motor unit firing rate analysis, analysis of interference pattern recording at different force levels, surface electromyography (EMG), single fibre EMG, macro-EMG and motor unit number estimation (MUNE).[20]

Conventional nerve conduction studies (NCSs) were performed in the form of motor (MCSs) and sensory (SCSs) conduction studies. In MCSs, the responses were evoked by electrical stimulation through a bipolar stimulator, distally and then proximally. The active electrode (G1) was placed over the midpoint of the muscle belly, and the reference electrode (G2) was placed 3 cm distally. The ground electrode was placed around the wrist for upper limb nerves and around the ankle between the active electrode and the stimulator for lower limb nerves. The left ulnar, right deep peroneal and left posterior tibial nerves were studied in MCSs. The SCSs were elicited with surface recording electrodes on the left ulnar and the right sural nerves.[21]

The compound motor action potential (CMAP) and the sensory nerve action potential (SNAP) were then assessed according to the following parameters: distal latency (msec) for the CMAP and peak latency (msec) for the SNAP, amplitudes from baseline to negative peak (mV and μV, respectively), and conduction velocity (m/sec). It was specified that a minimum of three abnormal variables in two or more nerves were required to diagnose polyneuropathy.[22] The abnormal findings were classified into axonal and demyelinating patterns.[21]

Spike-triggered averaging (STA) technique, which was pioneered by Brown and colleagues in 1988, employ a needle electrode to detect the activities of single motor units during weak voluntary contraction; each discharge of the motor unit recorded by the needle triggers an averaging device, receiving its input from another surface electrode over the muscle, which helps to largely eliminate the background 'noise' generated by other active units.[23]

In this study, motor unit analysis and MUNE calculation were performed by using a modified form of the spike-triggered technique,[23] in which a surface electrode instead of a bipolar needle electrode was used. The maximum M-wave was elicited from the left abductor digiti minimi muscle by supramaximal stimulation of the left ulnar nerve at wrist. Supramaximal stimulation was achieved when no further increase in the amplitude of the M-response occurred, even after the stimulus intensity was increased by 25%.

This supramaximal stimulation was essential to ensure stimulation of all the fibres within the nerve. Markers indicating the negative onset, negative peak amplitude and positive peak were automatically positioned, and the size-related parameters of the M-wave were automatically calculated. For the single motor unit potential analysis (S-MUP), the subjects were asked to minimally contract the muscle isometrically while the surface electrode was maintained in a stable position and the trigger line was set at 200 μV.

Each isometric contraction lasted for 30 sec, with rest periods of 30–60 sec provided between contractions. Frequency of firing of motor units was checked after each trial to ensure not activating more than one motor unit according to law of modulation (not exceeding 10/sec, frequency of firing was automatically measured by the machine). Subjects were instructed to maintain consistent intensities throughout the contraction.

The contractions were performed until a minimum of 15 MUP trains were obtained. The surface detected MUP waveforms were visually checked to ensure that the onset and peak markers were accurate (Figure 1). Filters were adjusted from 10 Hz to10 kHz, sweep duration was set at 50 msec, sensitivity at 200 μV and trigger line at 200 μV. The MUNE equals the CMAP amplitude divided by the mean amplitude of the S-MUP.[24]

Figure 1.

MUNE calculation using the modified spike-triggered technique. A, minimal isometric voluntary contraction of the abductor digiti minimi muscle with the trigger line set on 200 μV (arrow). B, superimposed motor unit potentials (MUPs) during minimal isometric contraction, using an amplitude triggered MUP programme. C, Averaged MUP with the cursors applied to get baseline-peak amplitude. D, Automatic analysis to get mean amplitude of averaged MUPs

Statistical Methods

Data were coded and entered using the statistical package for the Social Sciences (SPSS) version 26 (IBM Corp., Armonk, NY, USA). Data were summarized using mean, standard deviation, median, minimum, and maximum for quantitative data and using frequency (count) and relative frequency (percentage) for categorical data. Comparisons between quantitative variables were done using the nonparametric Kruskal-Wallis and Mann-Whitney tests. For comparisons of categorical data, the chi-square (χ2) test was performed. The exact test was used instead when the expected frequency was less than 5. Correlations between quantitative variables were done using the Spearman correlation coefficient. A p value less than 0.05 was considered statistically significant.

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