Purpose: Postactivation depression of the Hoffmann reflex is reduced in Parkinson's disease (PD), but how the recovery is influenced by the state of the muscle is unknown. The present pilot study examined postactivation depression in PD at rest and during a voluntary contraction while patients were off treatment and while receiving medications and/or deep brain stimulation.
Methods: The authors recruited nine patients with PD treated with implanted deep brain stimulation and examined postactivation depression under four treatment conditions. Paired pulses were delivered 25 to 300 ms apart, and soleus Hoffmann reflex recovery was tested at rest and during voluntary plantar flexion. Trials were matched for background muscle activity and compared with 10 age-matched controls.
Results: Patients with Parkinson disease who were OFF medications (OFF meds) and OFF stimulation (OFF stim) at rest showed less postactivation depression at the 300 ms interpulse interval (86.1% ± 21.0%) relative to control subjects (36.4% ± 6.1%; P < 0.05). Postactivation depression was restored when dopaminergic medication and/or deep brain stimulation was applied. Comparisons between resting and active motor states revealed that the recovery curves were similar OFF meds/OFF stim owing to faster recovery in PD seen at rest. In contrast, the effect of the motor state was different ON meds/OFF stim and ON meds/ON stim (both P < 0.05), with a nonsignificant trend OFF meds/ON stim ( P > 0.08). During a contraction, recovery curves were similar between all treatment conditions in PD and control.
Conclusions: Disrupted Hoffmann reflex recovery is restored to control levels in PD patients at rest when receiving medications and/or deep brain stimulation or when engaged in voluntary contraction.
Copyright © 2020 by the American Clinical Neurophysiology Society.