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

Area of Science:

• Neuroscience
• Clinical Neurology

Background:

• Functional movement disorders (FMD) are often associated with exaggerated startle reactions.
• Previous research has suggested long onset latencies and inconsistent muscle recruitment in FMD patients.
• The auditory startle reflex in FMD has not been systematically investigated.

Purpose of the Study:

• To evaluate the frequency and pattern of early and late auditory startle response components in patients with functional jerky movement disorders.
• To compare these responses between FMD patients and healthy controls.

Main Methods:

• A case-control study involving 17 FMD patients and 15 healthy controls.
• Auditory startle reflex elicited using 108 dB loud tones.
• Electromyography used to assess muscle responses.

Main Results:

• Patients with FMD showed significantly enlarged response probabilities for both early and late auditory startle responses.
• The early response exhibited a normal muscle recruitment pattern, while the late response showed more variability.
• Normal habituation of both early and late responses was observed in both groups.
• A high response rate of abdominal muscles was noted, particularly in patients with abdominal jerks.

Conclusions:

• Functional movement disorders are characterized by enlarged early auditory startle responses with normal patterning.
• The high frequency of late responses in FMD patients indicates a behavioral component.
• Findings support the notion of hypersensitivity to external stimuli in FMD, evidenced by increased auditory startle response probabilities.