Characterization of Involuntary Contractions after Spinal Cord Injury Reveals Associations between Physiological and Self-Reported Measures of Spasticity.

Meagan Mayo,Mabelin Castellanos,Bradley A. DeForest,Christine K. Thomas

doi:10.3389/fnint.2017.00002

Meagan Mayo, Mabelin Castellanos + Show 2 more

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https://doi.org/10.3389/fnint.2017.00002

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Abstract

Correlations between physiological, clinical and self-reported assessments of spasticity are often weak. Our aims were to quantify functional, self-reported and physiological indices of spasticity in individuals with thoracic spinal cord injury (SCI; 3 women, 9 men; 19–52 years), and to compare the strength and direction of associations between these measures. The functional measure we introduced involved recording involuntary electromyographic activity during a transfer from wheelchair to bed which is a daily task necessary for function. High soleus (SL) and tibialis anterior (TA) F-wave/M-wave area ratios were the only physiological measures that distinguished injured participants from the uninjured (6 women, 13 men, 19–67 years). Hyporeflexia (decreased SL H/M ratio) was unexpectedly present in older participants after injury. During transfers, the duration and intensity of involuntary electromyographic activity varied across muscles and participants, but coactivity was common. Wide inter-participant variability was seen for self-reported spasm frequency, severity, pain and interference with function, as well as tone (resistance to imposed joint movement). Our recordings of involuntary electromyographic activity during transfers provided evidence of significant associations between physiological and self-reported measures of spasticity. Reduced low frequency H-reflex depression in SL and high F-wave/M-wave area ratios in TA, physiological indicators of reduced inhibition and greater motoneuron excitability, respectively, were associated with long duration SL and biceps femoris (BF) electromyographic activity during transfers. In turn, participants reported high spasm frequency when transfers involved short duration TA EMG, decreased co-activation between SL and TA, as well as between rectus femoris (RF) vs. BF. Thus, the duration of muscle activity and/or the time of agonist-antagonist muscle coactivity may be used by injured individuals to count spasms. Intense electromyographic activity and high tone related closely (possibly from joint stabilization), while intense electromyographic activity in one muscle of an agonist-antagonist pair (especially in TA vs. SL, and RF vs. BF) likely induced joint movement and was associated with severe spasms. These data support the idea that individuals with SCI describe their spasticity by both the duration and intensity of involuntary agonist-antagonist muscle coactivity during everyday tasks.

Highlights

Spasticity is defined classically as a velocity-dependent increase in resistance to passive stretch (Lance, 1980), but clinically it presents as increased muscle tone, hyperreflexia and/or involuntary muscle contractions
The involuntary Electromyographic activity (EMG) signals generated during a necessary daily task were recorded once at the start of one (n = 3) or two experiments (n = 4) in those individuals with spinal cord injury (SCI) who were capable of unassisted transfers as a functional measure of spasticity
Correlations within Transfer Intense EMG in rectus femoris (RF) was associated with high intensity EMG in biceps femoris (BF) (ρ = 0.786, p = 0.036) and tibialis anterior (TA) (ρ = 0.893, p = 0.007)

Summary

Introduction

Spasticity is defined classically as a velocity-dependent increase in resistance to passive stretch (Lance, 1980), but clinically it presents as increased muscle tone, hyperreflexia and/or involuntary muscle contractions (spasms; Adams and Hicks, 2005). Electromyographic activity (EMG) has been used to document the various types of involuntary muscle contractions that occur during daily tasks (Tepavac et al, 1992; Winslow et al, 2009; Thomas et al, 2014), or imposed movements (Benz et al, 2005), when tone is assessed using the Ashworth scale (Sköld et al, 1998; Sherwood et al, 2000; McKay et al, 2004), as muscles are stretched passively (Burke et al, 1971), or when people with SCI walk (e.g., Yang et al, 1991; Harkema, 2001; Kressler et al, 2014). Self-reported spasm frequency scores correlated poorly with clinical assessment of perceived resistance against passive movement of the limb (i.e., tone using the modified Ashworth scale) or tendon reflexes (Priebe et al, 1996; Baunsgaard et al, 2016)

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