The Hyperekplexias and Their Relationship to the Normal Startle Reflex

Abstract

The startle response to unexpected auditory and somaesthetic stimulation was studied in 8 patients with hereditary or symptomatic hyperekplexia. It was abnormal in its resistance to habituation and in its exaggerated motor response. Both noise and taps to the face and head elicited a normal early blink response, separate from the subsequent true startle reflex. The earliest reflex EMG activity recorded after the blink was in sternocleidomastoid. EMG activity in masseter, and trunk and limb muscles followed later. This pattern of muscle recruitment suggests a brainstem origin for the abnormal startle responses. In addition, the abnormal startle responses exhibited disproportionately long latencies to the intrinsic hand and foot muscles and relatively slow recruitment of caudal muscles. The pattern of muscle recruitment was similar between patients, irrespective of the absolute latency of the response, and regardless of whether stimulation was auditory or somaesthetic. This suggests that auditory and somaesthetic afferents converge on a common brainstem efferent system, and that this system forms the final common pathway for abnormal startle responses of differing latency. The characteristics of this efferent system differ from those previously described in brainstem reticular reflex myoclonus, but are similar to those described in the normal auditory startle reflex in man. This suggests that the abnormal startle response in hyperekplexia, and the normal startle reflex represent pathological and physiological activity in the same brainstem efferent system.

Stimulus-Induced Drop Episodes in Coffin-Lowry Syndrome

“…Hyperekplexia is defined as an exaggerated motor response to auditory, somesthetic, or visual stimuli that is resistant to habituation and may be characterized by either a brief pathologic startle reflex or a sustained tonic spasm. 12 An appropriate stimulus produces a …”

The Startle Pattern in the Minor Form of Hyperekplexia

“…The paucity of responses of the biceps and thenar muscles made the comparison less reliable. The onset latencies of the orbicular muscle of the eye were not prolonged in the minor HE com pared with those in the control group, but their analysis is com plicated because they comprise 2 types of reflexes: the startle reflex and the blink reflex.15 Pro longed onset latencies in a patient with the hereditary minor HE were also described by Brown et a l 10 Mean onset latencies increased in the 4 muscles in the follow ing order: the orbicular muscle of the eye, the sterno cleidomastoid muscle, the biceps muscle, and the the nar muscle in the 2 patient groups in our study, which may be caused by the innervation of the muscles from the startle generator.10 In the control group, the onset latency of the thenar muscle was shorter than that of the biceps muscle, but this may be caused by the small number of thenar responses. The onset latencies in the minor HE group were too long to be compatible with a startle response; the same refers to the differences in latencies between the sternocleidomastoid and the biceps muscles (51.8 milliseconds) and between the biceps and thenar muscles (53.2 milliseconds),10, 15 Thompson et al16 investigated voluntary stimulussensitive jerks in patients and controls and found that it was possible to distinguish voluntary jerks from the ste reotyped electrophysiological characteristics of the startle response of brain-stem origin.…”

Neonatal-Onset Brainstem Reticular Reflex Myoclonus Following a Prenatal Brain Insult: Generalized Myoclonic Jerk and a Brainstem Lesion

“…Electromyography showing exaggerated, synchronized rhythmic myoclonic contraction of all extremities, which was easily elicited by sensory stimulation, was more compatible with BRRM (Brown et al 1991;Rothwell 1996;Hallett 2002) than with other types of myoclonus, including that of cortical or spinal origin, although additional electrophysiological data were not available. The possibility of hyperekplexia was ruled out by examining GLRA1 gene mutation.…”

“…The acute type has not been studied intensively but probably originates in the brainstem (Hallett 2000). One such condition is brainstem reticular reflex myoclonus (BRRM), characterized by sudden generalized shock-like movements that can be elicited by sensory stimulation (Brown et al 1991;Rothwell 1996). Most patients who develop post-hypoxic myoclonus are between the ages of 15 and 60 years (Frucht 2002), whereas such movement disorders are very rarely reported in childhood.…”