Specific brainstem and cortico-spinal reflex abnormalities in coexisting essential tremor and Parkinson's disease...

We aimed to analyze functional changes at brainstem and spinal levels in essential tremor (ET), Parkinson's disease (PD) and coexisting essential tremor and Parkinson's disease (ET-PD).

Age- and gender-matched patients with tremor (15 ET, 7 ET with resting tremor, 25 ET-PD and 10 PD) and 12 healthy subjects were enrolled in the study. Diagnosis was established according to standardized clinical criteria. Electrophysiological studies included blink reflex (BR), auditory startle reaction (ASR) and long latency reflex (LLR).

Blink reflex was normal and similar in all groups. Probability of ASR was significantly lower in ET-PD group whereas it was similar to healthy subjects in ET and PD (P<0.001). LLR was recorded during voluntary activity in all three groups. LLR II was more common in ET, PD and ET-PD groups. LLR III was far more common in the PD group (n=3, 13.6% in ET; n=4, 16.0% in ET-PD and n=7, 46.7% in PD; p=0.037).

Despite the integrity of BR pathways, ASR and LLR show distinctive abnormalities in ET-PD. In our opinion, our electrophysiological findings support the hypothesis that ET-PD is a distinct entity.