Effect of Motor State on Postactivation Depression of the Soleus H-Reflex in Parkinson's Disease During Deep Brain Stimulation and Dopaminergic Medication Treatment: A Pilot Study.

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 0.08). 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.