Startle reflex in neurocritical brainstem patients

Background Patients in a neurocritical condition with lesions involving the brainstem cannot cooperate with electrophysiological examination and, therefore, it may be difficult to determine what are the main functions affected. We have used two tests to characterize the deficit in the motor domain, transcranial magnetic stimulation (TMS) to induce motor evoked potentials (MEPs) and loud auditory stimulation (LAS) to induce the startle reflex (SR). Methods The study was done in 5 patients who were in their acute/subacute phase after brainstem involvement because of neoplastic tumors (1 cavernoma and 1 meningioma), vascular lesions (1 ictus and 1 haemorrhage) and meningitis with cranial nerve involvement (1 patient). TMS was applied with a round coil or a double-cone coil over the vertex. LAS was applied by discharging the coil flat on top of a metallic platform. Results MEPs were obtained in three patients at normal latency while they were absent in the remaining two patients. Attempts of voluntary contraction to facilitate responses did not change the results. The SR was present in two patients (one of them with normal MEPs). Three patients had no startle response. Normal MEPs and SRs were observed only in the patient with meningitis. Conclusion There was no clear association between presence or absence of SRs and the standard neurological examination in our patients. Apart from direct lesions in nuclei or tracts, we should also consider alterations in excitability as one of the explanations for absence of SR or MEPs.