Approach to exaggerated startle reflex: a case of hyperekplexia minor

Correspondence to Dr Haris Hakeem; [email protected]

Background

The ‘startle’ (Greek: sudden shock or alarm) reflex (SR) is a physiological phenomenon that occurs in response to a sudden unexpected stimulus.¹ Evolutionarily, it can be considered a protective reflex which orients the body towards the perceived threat and prepares it to take an appropriate action (fight or flight).² The reflex is mediated by the caudal brainstem and consists of a generalised, symmetrical and synchronous activation of muscles causing flexion at the neck, trunk, elbow, hips and knees along with facial grimace and abduction of shoulders¹; the movements predominantly involving the upper body. The inciting stimuli are mostly auditory and tactile but can also be visual and vestibular. This normal phenomenon may become exaggerated in terms of magnitude and lack of habituation, and a lower threshold, referred to as ‘exaggerated startle reflex’.^{1 3} An exaggerated SR has broad differential and given overall rarity, poses a diagnostic challenge. We report a case of exaggerated SR and discuss all the diagnostic possibilities with etiological categories and clinical features helpful in characterisation.

Case presentation

A 39-year-old man without known comorbid conditions, presented in our neurology clinic with 13-year history of brief generalised body jerks triggered by sudden unexpected auditory or tactile stimuli, the latter especially over the shoulders or back of the upper trunk. He reported onset after a brief febrile illness. These episodes were not associated with loss of consciousness or falls. The jerks were strictly stimulus sensitive without any premonitory sensation and were not suppressible (see video 1). He did not notice any variability with caffeine intake or stress and had never taken alcohol.

The patient had never had any seizures. There were no symptoms to suggest any systemic medical illness. His parents were unrelated and there was no family history of similar symptoms. He denied alcohol use or a significant medication history. The neurological examination otherwise did not reveal any abnormality. Specifically, no startle response was elicited on tactile stimulation of the hands.

Investigations

MRI of the brain was unremarkable. Electroencephalography (EEG) with recording of exaggerated SR did not show any epileptiform correlation.

Treatment

Tablet clonazepam 0.5 mg every night at bedtime (qHS) was prescribed along with reassurance regarding the benign nature of...