Measurement of the effect of a bolus dose of intrathecal baclofen by continuous measurement of force under fibreglass casts

Abstract

Continuous intrathecal administration of baclofen with implanted programmable pump systems is recommended in the treatment of severe spasticity of cerebral origin. Prior to pump implantation, a baclofen bolus test (BBT) is used to assess the effectiveness of intrathecal baclofen using the modified Ashworth Scale (MAS) and Penn Spasm Frequency Scales (SFS). The result of a BBT may be difficult to interpret in patients with reduced joint mobility caused by contractures. The aim of this study was to apply a new spasticity measurement which would quantify and visualise the effect of a BBT in 10 patients with severe cerebral spasticity and contractures. Spasticity was recorded continuously by the measurement of force under circular fibreglass casts in 10 knee joint contractures. Force was recorded as net-torque by multiplying the force and distance between sensor and joint axis, thus allowing inter-individual comparison. MAS, SFS, and two three-hour time integrals of net-torque were determined before and after intrathecally administered baclofen. No significant changes in MAS (p = 0.1) and SFS (p = 0.07) were observed; however, a significant reduction of time integrals of net-torque after baclofen administration (p = 0.005) was found. The present study shows that the antispastic effect of intrathecally administered BBT can be quantitatively assessed and visualised using the described method. It also suggests that this method can be helpful in the assessment of the effectiveness of the BBT in patients with severe spasticity of cerebral origin and contractures.

Time course of the effect of a bolus dose of intrathecal baclofen on severe cerebral spasticity

“…To quantify the muscle work under the cast and to avoid an influence of the casting procedure on spasticity measurement, periods of 30-minute time integrals of net-torque (TI [Nm·s]= net-torque [Nm] × time [s]) were calculated from the recordings 9 hours before to 22.5 hours after the BBT [18]. TI -9 indicates the time integral of net-torque between 9 and 8.5 hours before BBT, TI -8.5 the time integral between 8.5 and 8 hours before BBT, and so on.…”

“…The spasticity measurement method has been described in detail in a previous publication of the authors [18]. This method will be briefly described below:…”

“…Claims as to the point of maximal effect of the BBT also vary in the medical literature [18,24], being between 4 to 6 hours in post-stroke patients [14], and between 3 to 4 hours in patients with traumatic brain injury [13]. Thus recommendations vary for the timing of the assessment of the clinical scales after the BBT [24].…”

“…A previous study by the authors has shown that spasticity during the BBT can be continuously and quantitatively measured by the measurement of force under fibreglass casts [18]. The aim of this study was to determine the time course of the effect of a BBT on severe cerebral spasticity using this method.…”

“…s Key words intrathecal baclofen · muscle spasticity · measurement of spasticity · baclofen bolus test The evaluation of the effect of intrathecal baclofen administration on spasticity relies on clinical assessments, such as the Modified Ashworth Scale (MAS), Penn Spasm Frequency Scale (SFS), motor scores or observation of patients' abilities, and recording of adverse effects [15,18,20].…”