Startle responses in functional jerky movement disorders are increased but have a normal pattern

Background: Exaggerated startle reactions have been frequently described in patients with functional movement disorders (FMD). Long onset latencies and inconsistent recruitment pattern are thought to be a hallmark in these patients. The auditory startle reflex has not been systematically assessed though. Objectives: Assessing the frequency and pattern of the early and late component of the auditory startle response in patients with functional jerky movement disorders. Methods: A case-control design was used to study 17 patients with functional jerky movement disorders and 15 healthy gender- and age-matched control subjects. The auditory startle reflex was elicited by 108 dB loud tones and assessed with electromyography in multiple muscles. Results: Response probability of the early and the late response were significantly enlarged in patients with FMD. The early response showed a normal muscle recruitment pattern whereas the late response revealed a more variable pattern compared to controls. The early and late responses showed normal habituation in both groups. Remarkably, a high response rate of the abdominal muscle was noted especially in patients suffering from abdominal jerks. Conclusions: This study shows enlarged, but normally patterned early startle responses in FMD. The high response frequency of the late responses found in these patients reflects a behavioral component. Hypersensitivity to external stimuli, often noted in FMD is supported by high response probabilities of both components of the auditory startle response. (C) 2017 Elsevier Ltd. All rights reserved.