Electrical Impedance Myography for Assessing Paraspinal Muscles of Patients with Low Back Pain

Abstract

The objective of this study was to determine the potential value of electrical impedance myography (EIM) for assessing lumbosacral paraspinal muscle (LPM) condition in lower back pain (LBP) patients. Standard methods for assessing the condition of LPMs, such as magnetic resonance imaging, are inconvenient and expensive. One tool that could be useful for this purpose is electrical impedance myography (EIM) a technique that can be performed rapidly at the bedside. After undergoing a screening history and examination, subjects were studied with the mView EIM device (Myolex, Inc, Boston). Bilateral LPMs were measured three times each and the two closest sets of measurements averaged on each side. Data analysis included non-parametric two-group comparisons between healthy subjects and back pain patients, receiver-operating curve analyses, and correlation analyses to age and body mass index. A total of 86 healthy individuals (median age (interquartile range) (IQR), 45.5 years (30.3-56.0 years), 42 men, 44 women) and 47 LBP (median age 51.0 year (39.5-57.5) years, 21 men, 26 women) were enrolled. Median EIM 100kHz phase was lower in the LBP patients (9.3°(IQR 8.4°-10.6°) versus 11.4°(IQR 9.4°-13.0°), p = 0.0007). Significantly increased normalized side-to-side differences were present for all three EIM variables (e.g., median 100 kHz phase 0.15 (IQR 0.07-0.31 in LBP patients versus 0.09 (IQR 0.04-0.17) in healthy individuals). A significant correlation between 100 kHz EIM phase and reactance was found with age (R_spearman=-0.46, P=0.0002 and R_spearman=-0.440, P=0.0003) but not for resistance. This study provides early evidence supporting that EIM has the potential to serve as a useful tool for evaluating the condition of LPMs.

Keywords: Low back pain; age; asymmetry; bioimpedance; body mass index; electrical impedance; musculoskeletal; paraspinal muscles; radiculopathy.

Figure 1

A. The Myolex mView^TM system for neuromuscular assessment, including laptop, power convertor box, impedance measuring unit, and electrode array; B. Detail of electrode array used in this study; magenta-current emitting, blue-voltage sensing. Only data from these 4 electrodes were used in this analysis.

Figure 2

Typical multifrequency data obtained from with the mView impedance-measuring system shown in Figure 1. This data is from a 34-year-old healthy volunteer.

Figure 3

A, B, C. The phase, resistance, and reactance values at 100 kHz (±standard deviation) for low back pain patients versus healthy controls. D, E, F. Receiver operating characteristic (ROC) plots for these same values. While the population means may be different, this analytical approach has limited value in discriminating between LBP patients and healthy individuals.

Figure 4

A, B, C. Relative differences in 100 kHz values (absolute value (right-left difference /right-left average)) for low back pain patients versus healthy controls. D, E, F. ROC plots for these same values. The D-value is equal to the side-to-side difference divided by the average of both sides. While still not a strong discriminator, this approach is stronger.

Figure 5

A, B, C. Correlation between phase, resistance, and reactance values at 100 kHz and age. Both phase and reactance show a significant relationship, whereas resistance does not. D, E, F. Correlation between phase, resistance, and reactance values at 100 kHz and age. Both phase and resistance show a significant relationship, whereas reactance does not.