Early modification of stretch reflex in Parkinson's disease.

We stretched quadriceps femoris in healthy subjects and in patients with a recent diagnosis of PD in order to assess whether modifications of the long-latency component of the stretch reflex is an early event in the course of Parkinson's disease (PD). We found a modified mechanical and electromyographic (EMG) behavior in stretching relaxed muscles of patients while voluntary activation greatly reduced differences between normal and Parkinsonian subjects, suggesting that a lower threshold of the response is an early sign in PD.