Case Report: Auditory Neuropathy and Central Auditory Processing Deficits in a Neuro-Otological Case-Study of Infratentorial Superficial Siderosis

Abstract

Hearing and balance impairment are the most frequently reported features of infratentorial (classical) superficial siderosis (iSS). There are few comprehensive descriptions of audiovestibular function in iSS and therefore limited understanding of the affected segment(s) of the audiovestibular pathway. In addition, monitoring disease progression and response to treatment is challenging and currently mainly guided by subjective patient reports and magnetic resonance imaging. To the best of our knowledge, there have been no previous reports assessing central auditory function in iSS. We describe such findings in a patient with iSS in an attempt to precisely localize the site of the audiovestibular dysfunction, determine its severity and functional impact. We confirm the presence of (asymmetrical) auditory neuropathy and identify central auditory processing deficits, suggesting involvement of the central auditory pathway beyond the brainstem. We correlate the audiological and vestibular findings with self-report measures and the siderosis appearances on brain magnetic resonance images.

Classical infratentorial superficial siderosis of the central nervous system: pathophysiology, clinical features and management

“…Absence of hearing difficulty should lead to questioning the diagnosis. iSS-related hearing loss is characterised as bilateral sensorineural of both cochlear and retrocochlear origin 4 24–26. It can be asymmetric, of variable degree, ranging from mild-to-moderate to severe-to-profound 24–26.…”

“…Gradual involvement of mid- and low-frequencies and overall deterioration of hearing thresholds may occur with disease progression 4 25. There are few dedicated studies on vestibular assessment in iSS, describing mixed central (cerebellar) and peripheral vestibular impairment, likely due to involvement of the cerebellar structures, vestibular nerves and end organs 24 26. Impaired balance is a major symptom, usually with a broad-based ataxic gait, usually worse in the dark; in severe cases this may progress to truncal ataxia and inability to sit or walk unassisted.…”

“…Additional tests of otoacoustic emissions, auditory brainstem-evoked responses, speech-in-noise and ‘central’ tests of hearing can be helpful, dictated by the hearing levels, the patient’s symptoms and other characteristics (comorbidities, previous ear, nose and throat (ENT) history, CNS surgery or trauma). We previously identified progressive interval changes on pure-tone audiometry and auditory brainstem-evoked responses in iSS, probably reflecting disease progression 26. Vestibular tests may help to determine the deficit pattern and vestibular rehabilitation plan; potentially useful tests include videonystagmography and video head-impulse test (contraindicated if there has been recent CNS surgery, ventriculoperitoneal shunting, abnormal intracranial pressure, history of cervical immobility) 24 26 34 35.…”

“…Vestibular tests may help to determine the deficit pattern and vestibular rehabilitation plan; potentially useful tests include videonystagmography and video head-impulse test (contraindicated if there has been recent CNS surgery, ventriculoperitoneal shunting, abnormal intracranial pressure, history of cervical immobility) 24 26 34 35. Caloric testing may be performed to assess (horizontal) semicircular canal/superior vestibular nerve involvement, while vestibular evoked myogenic potentials assess otolith end organ and vestibular nerve function 26…”

“…iSS-related hearing loss is characterised as bilateral sensorineural of both cochlear and retro-cochlear origin 4 24 25 . It can be asymmetric, of variable degree, ranging from mild-to-moderate to severe-to-profound [24][25][26] .There is often sparing of low-frequencies and mid-frequencies in the early stages of disease, with down-sloping configuration on pure-tone audiometry (PTA), which may be misdiagnosed as age-related hearing loss 25 . Its onset in iSS, however, may be earlier than in agematched populations 24 25 .…”