Spasticity Deciphered: The effects of intrathecal baclofen treatment determined by electromyography in spasticity

Abstract

Background
Spasticity is a condition that affects patients who have sustained an upper motor neuron lesion. Such lesions include for example cerebral palsy (CP), of which 35% is affected by spasticity, and stroke, of which 90% is affected by spasticity. Pharmacological therapy often involves the prescription of oral baclofen. However, due to the difficulty of medication in crossing the blood-brain barrier, high dosages of oral baclofen are required to achieve the desired therapeutic effect, which in turn leads to an increase of the incidence of negative side-effects. For patients with severe spasticity, the intrathecal baclofen (ITB) pump is indicated for more effective drug delivery. To monitor the efficacy of the treatment and quantify the level of spasticity, the Modified Ashworth Scale (MAS) is employed. Nevertheless, the moderate inter- and intra-rater reliability indicates that the subjectivity of the approach represents a potential limitation. Therefore, a more objective approach is required. Surface electromyography (sEMG) can measure direct muscle activity and is an objective and non-invasive approach. Yet, there is no research available on sEMG measurements to assess the change in muscle activity as a result of ITB treatment.

Objective
The primary objective of this exploratory study is to assess the effect of intrathecal baclofen on lower limb muscle activity using sEMG. The secondary objectives are assessing the correlation between the sEMG feature values and MAS scores, and between the sEMG feature values and Patient's Global Impression of Change (PGIC) scores.

Method
sEMG measurements were performed during standard assessment of the MAS on patients receiving an ITB single shot trial (SS) and/or pump implantation. The following features were analyzed: (1) Root Mean Square (RMS), (2) Peak Amplitude Value (PAV), (3) Median Frequency, and (4) Co-Contraction (CCR). A comparative analysis was conducted to assess the change in mean feature value of each individual muscle between pre- and post-treatment for the purpose of study aim 1. The Spearman's rank correlation coefficient was calculated in order to assess the relationship between changes in feature values and changes in MAS scores. Furthermore, the Spearman's rank correlation coefficient was calculated to assess the relationship between the changes in most effective feature and the PGIC scores.

Results
A total of twelve patients were included in the study, diagnosed with a variety of conditions including spinal cord injury (SCI), multiple sclerosis (MS), traumatic brain injury (TBI) and CP. Following ITB treatment, the RMS demonstrated a statistically significant decrease for three out of eight muscles: the left semitendinosus (p = 0.020), the right rectus femoris (p = 0.025) and the right tibialis anterior (p = 0.002). The PAV presented a decrease in 3-8 out of 10 patients following SS baclofen treatment. The changes in median frequency exhibited considerable variability between patients following ITB treatment. The CCR decreased in six out of ten patients for the left leg following SS baclofen treatment. A significant correlation was observed between the change in MAS scores and change in RMS in the medial gastrocnemius (p = 0.027) and the change in median frequency in the semitendinosus (p = 0.002). A low correlation was observed between the change in RMS and the PGIC score.

Conclusion
In conclusion, this study demonstrates the potential of sEMG features, such as RMS, in assessing the impact of ITB treatment on muscle activity. Future work could validate these findings by increasing the sample size and improving certain methodological aspects.