Objective: To explore the brainstem function in patients with idiopathic normal pressure hydrocephalus (iNPH) by means of a multimodal electrophysiological assessment of trigeminal, facial, and auditory pathways.

Background: Hearing dysfunction in iNPH patients has been hypothesized as a result of endolymphatic or perilymphatic hydrops caused by abnormal cerebrospinal fluid dynamics. However, it is unclear whether a superimposed damage of brainstem auditory pathways is involved. In parallel, a preliminary study has showed impairment of R2 component of the blink reflex recovery cycle underlying brainstem hyperexcitability in iNPH patients. This latter evidence could derive from the compressive damage of enlarged ventricles on the brainstem. Nonetheless, further evidences evaluating the trigeminal-facial integration are lacking.

Method: We recruited 15 patients with probable iNPH (eight males; age: 76.8 ± 4.3 years) according to the iNPH International Guidelines, and ten age-matched controls who had no neurological symptom and a normal neurological examination. All subjects performed brainstem auditory evoked potentials and electrophysiological assessment of the blink reflex and jaw jerk reflex.

Results: As compared to the controls’ cohort, at brainstem auditory evoked potentials iNPH patients had a higher hearing threshold, prolonged latencies of waves I and III bilaterally (p < 0.01), and increased values of I-III interpeak interval on the left side (p < 0.05). We did not found any between-group differences with regard to latencies of R1 and R2 components of the blink reflex. In addition, iNPH patients showed prolonged latencies of R1 component of the jaw jerk reflex bilaterally (p < 0.01).

Conclusion: Electrophysiological features of iNPH patients could be an auditory dysfunction at the level of cochlea, cochlear nerve, or caudal pons, together with impairment of the mesencephalic nucleus of trigeminal nerve involved in the monosynaptic masseter reflex. The abnormal cerebrospinal fluid dynamics leading to enlargement of the ventricular spaces in iNPH could affect the physiology of inner ear fluids, cochlear nerve, and midbrain in these patients.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/electrophysiological-evaluation-of-brainstem-function-in-patients-with-idiopathic-normal-pressure-hydrocephalus/