Acoustic startle response in patients with orthostatic tremor

Background and aimOrthostatic tremor is a high frequency tremor predominantly on calf muscles during standing. Brainstem is the most probable generator in the pathogenesis since it comprises bilaterally projecting centers regulating stance or tone. We aimed to investigate the functional role of brainstem through the evaluation of acoustic startle response in primary orthostatic tremor patients.Patients and methodWe included 7 (2 males) consecutive patients and 13 (5 males) healthy volunteers. Diagnosis was confirmed by polymyographic surface electromyography. All subjects underwent acoustic startle response and blink reflex investigations.ResultsPresence rate (71.4% vs. 100%, p = 0.042) and response rate (27.5% vs. 40.5%, p = 0.047) of total acoustic startle response were lower in patient group. Similarly, probability over orbicularis oculi was lower among patients (p = 0.003). However, blink reflex was observed in all patients and healthy volunteers and latencies of startle and blink reflexes were similar between groups.ConclusionsIn our patient group, normal response rate and latencies of R1 and R2 show structural integrity of at least blink reflex circuit at brainstem. On the other hand, suppressed response rates probably reflect decreased excitability of auditory startle reflex pathway.

► Response rates and latencies of R1 and R2 are normal.
► Auditory startle response (ASR) is suppressed.
► Normal blink reflex shows structural integrity of blink reflex circuit.
► Our results increase the possibility that brainstem and diencephalon serve as anatomic substrates in orthostatic tremor pathogenesis.