Article 9: Sensitivity of H-reflex in detecting response to complex-continuous mode of intrathecal baclofen delivery

Objective: To determine sensitivity of H-reflex in assessing spinal cord responsiveness before and after programming complex-continuous mode of intrathecal baclofen (ITB) delivery. Design: Prospective, consecutive sample. Setting: Traumatic Brain Injury Model Systems inpatient rehabilitation center. Participants: 7 patients with dysfunctional spasticity due to acquired brain injury underwent serial soleus H-reflex recordings before and 4 hours after the ITB delivery mode was changed from simple- to complex-continuous. Intervention: 25- to 125-μg ITB boluses during complex-continuous mode. Main Outcome Measures: The ratio between maximum H-reflex and maximum M wave (H/M). Results: Initial simple-continuous dose ranged from 150 to 490μg/d with the corresponding H/M ratios from 33% to 82%. After bolus administration, the H/M ratio decreased in 5 subjects from 10% to 60% in a dose-dependent manner. Corresponding change in mean Ashworth Scale score (n=3) was <0.7. In the remaining 2 subjects, only minimal change in H/M occurred; malfunctioning pumps were later found. Conclusions: Our results indicate that the H-reflex is a sensitive technique for monitoring spinal cord responsiveness to complex-continuous mode of ITB delivery. H-reflex recordings may be useful for ensuring proper pump function, especially when clinical spasticity is decreased due to simple-continuous ITB delivery and, therefore, less detectable by clinical evaluation.