Knee Muscle Stretch Reflex Responses After an Intrathecal Baclofen Bolus in Neurological Patients With Moderate-to-Severe Hypertonia.

OBJECTIVES

To examine the prevalence, onset threshold, and response magnitude of stretch reflex response (SRR) in the knee extensors and flexors before and after an intrathecal baclofen (ITB) bolus injection in patients with moderate-to-severe hypertonia.

MATERIALS AND METHODS

SRRs were elicited by reciprocal passive knee extension/flexion movements at preset angular velocities of 5, 60, 120, 180, 240, and 300°/s using an isokinetic dynamometer and recorded with surface electromyographic (EMG) electrodes placed over the knee extensors and flexors in 53 neurologic patients before and at 2.5 and 5 hours after an ITB injection via lumbar puncture. Outcome measures included the number of patients with presence/absence of SRRs, the number of SRRs per session, SRR onset threshold angle and velocity, and response magnitudes (peak EMG and area under the EMG curve) for each muscle. Pre-post comparisons were completed using the Fisher's exact and Wilcoxon signed rank tests.

RESULTS

For both knee extensors and flexors, the proportion of patients with present SRRs (p < 0.0001) and the number of SRRs per session (p ≤ 0.027) decreased from pre- to post-ITB. The threshold velocity significantly increased post-injection in both muscles (p ≤ 0.001) without significant changes in the threshold angle. The response magnitudes significantly decreased in the knee extensors (p ≤ 0.016) but not the knee flexors after the injection.

CONCLUSIONS

The prevalence and threshold velocity of SRR emerged as the most robust and practical parameters for assessing hyperreflexia during ITB bolus trial that can complement clinical assessment of muscle hypertonia.