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

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 clinical scales such as the Modified Ashworth Scale (MAS). In the literature, the time and period of maximum effect of a bolus dose of intrathecally administered baclofen in patients with cerebral spasticity is variously reported. The aim of the study was, therefore, to reveal the time course of the effect of a BBT on severe cerebral spasticity by the use of a recently described spasticity measurement method. Spasticity in knee joints of 13 patients with severe cerebral spasticity was repeatedly assessed using the MAS and also continuously recorded by the measurement of force under circular fibreglass casts. Force was recorded as net-torque by multiplying the force by the distance between sensor and joint axis, thus allowing inter-individual comparison. Half-hour time integrals (TI) of net-torque were determined 9 hours before and 22 hours after intrathecal baclofen administration. Post-BBT half-hour time integrals (TI+0, TI+0.5, to TI+22) were compared with the mean of 17 pre-BBT half-hour time integrals ((TI) over bar (-9 to-1)). Significantly lower post-BBT half-hour time integrals compared with (TI) over bar (-9 to -1) were found between TI+2 and TI+8 (Dunnett adjusted p < 0.05). The median lowest TI after BBT of the 13 patients was TI+4. The lowest mean MAS scores were found 4 hours after BBT. The findings suggest that the greatest effect of BBT on cerebral spasticity occurs between 2 and 8.5 hours, with a maximal effect at 4 hours after intrathecal baclofen injection. Clinical scales used to determine the effect of BBT should thus be carried out during this period - ideally at 4 hours after baclofen injection.