[Pathological jaw opening reflex after whiplash injury]

The brainstem mediated inhibitory reflex of the m. temporalis was investigated on average 3 days after the accident in 61 patients (f = 36; m = 25; mean age = 28 years +/- 9 SD) who presented an acute cervico-cephalic syndrome with posttraumatic headache and neck pain following acute whiplash injury but without neurological deficits, bone injury of the cervical spine or combined direct head trauma. We postulated a disturbed reflexive temporalis muscle inhibition in patients with 'whiplash cephalalgia', as has previously been reported for classical muscle tension headache. Latencies and durations of the early and late exteroceptive EMG suppression (ES1 and ES2) and the interposed EMG activity (IE) of the voluntarily contracted right temporalis muscle following ipsilateral stimulation of V/2 + 3 afferents were recorded. The reflex data were compared to a cohort of 69 age and sex matched normal subjects (f = 37; m = 32; mean age = 28 years +/- 7 SD). The following significant reflex changes were found in patients: a shortened duration of ES2 with delayed onset and premature ending, a slight prolongation of ES1 and IE, a delayed onset of IE and a diminished ratio of ES2:ES1 and ES2:IE. We conclude that the abnormality of the antinociceptive reflex is based on a transient dysfunction of the brainstem mediated reflex circuit following the acceleration trauma, which can be considered a neurophysiological correlate of the posttraumatic cervico-cephalic pain syndrome and may be useful as a 'biological marker' in monitoring the time course of recovery from pain.(ABSTRACT TRUNCATED AT 250 WORDS)