Neurophysiological insights into iNPH: ABR and CAEP responses to lumbar puncture and shunt surgery

BACKGROUND: Idiopathic normal pressure hydrocephalus (iNPH) is a neurological syndrome resulting from increased cerebrospinal fluid volume without significant increase in intracranial pressure. The diagnosis is difficult and investigating other tools that can assist in this process is essential. Auditory Evoked Potentials (AEPs) can be used to assess the auditory pathway integrity and monitor cognitive auditory functions. The objective of this study was to investigate the applicability of the AEPs as a potential monitoring tool for detecting clinical improvements associated with cerebrospinal fluid removal by lumbar puncture and VPS placement in patients with iNPH. METHODS: This longitudinal study, evaluated 17 individuals with iNPH, aged over 60 years who underwent the ventriculoperitoneal shunt, by Auditory Brainstem Response (ABR) and Cortical Auditory Evoked Potentials (CAEP) at three different times: before the lumbar puncture during the Tap test, two to four hours after the lumbar puncture, and after the ventriculoperitoneal shunt. RESULTS: A decrease in P3 latency was observed after lumbar puncture during Tap test. No statistically significant differences were observed between assessments for P1, N1 P2, N2 latencies or P1-N1, P2-N2 and N2-P3 amplitudes of the CAEP, as well as for the absolute and interpeaks latencies of the ABR. CONCLUSIONS: After the removal of significant volumes of cerebrospinal fluid in patients with iNPH, lower P3 latency values were found, suggesting an increase in the speed of acoustic information processing, during the Tap test. This result brings an insight on the applicability of this procedure as an auxiliary method for monitoring clinical improvements associated with cerebrospinal fluid removal in iNPH.