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Case history

This 54-year-old woman had presented to our clinic 11 years ago with a 16-year history of progressive hearing loss. Her medical history was significant for trauma at the age of 7 years. She was involved in a motor vehicle accident in which she had a head trauma and was unconscious for several days. This accident left her with balance and coordination problems. Five years before presentation, she had an abnormal magnetic resonance imaging (MRI) result and progressive ataxia and disequilibrium. Her brain MRI showed signal dropout on all sequences at the upper cerebellar hemispheric folia and vermis and in the region of the left sylvian fissure consistent with superficial siderosis (SS). She also had spasticity, which was felt to be due to an ectatic vertebral artery for which she underwent a vascular decompression. Biopsy of leptomeninges was also performed. An audiogram from that time revealed a bilaterally mild sloping to profound sensorineural hearing loss.

One year before her initial presentation, she developed hydrocephalus and had a ventriculoperitoneal shunt placed. She was subsequently found to have recurrent subarachnoid hemorrhages. She had a cholecystectomy, which was complicated by infection of her V-P shunt, which was subsequently removed.

At the time of presentation, she was using binaural hearing aids. She had been experiencing progressive hearing loss, which was documented with serial audiograms. She progressed to a flat profound hearing loss and 0% worse recognition bilaterally. Consultation was obtained with her neurologist seeking insight into the stability of her disorder. In particular, the requirement for future MRI scans was questioned. It was concluded that the concern for identifying subsequent significant intracranial bleeds could be met by computed tomography imaging. In 1999, she underwent cochlear implant pretesting and proceeded to receive a left cochlear implant, Nucleus 24 (Cochlear Limited, Lane Cove, Australia).

She did well initially; she had a speech recognition threshold of 34 dB, with 71% correct on Hearing in Noise Testing sentences. She continued to have good function for 5 years. Six years postimplant, she was found to have a warble tone threshold of 26 dB, but with only 25% correct on HINT sentences. This was a fairly abrupt change. Reprogramming was performed, her external hardware was switched, and an integrity test was performed on the internal system. The internal device performed normally on integrity testing. One month after the testing, she had a fall in which she hit her head. From then on, she reported hearing a buzzing sound with either of her 2 processors. Another integrity test was performed several months later; again, the result was normal. For the next 2 years, she has had progressive worsening of her function. Her ataxia, diplopia, and cognitive function were also worsening. She had another fall recently, which again punctuated a further decline in function. She had another integrity test in which the result was normal. She has undergone extensive reprogramming. She describes that she hears extra noise or static. Currently, she is using a map using only four channels and getting minimal benefit from it. However, she prefers this over the maps with more channels because she feels she only hears more noise.

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Discussion

Superficial siderosis is a rare condition that is characterized by recurrent subarachnoid bleeds leading to hemosiderin deposits in the leptomeninges, subpial tissue, spinal cord, brainstem, and/or the 8 nerves, resulting in eventual demyelination . Heme pigment and free iron are metabolized by glial cells. When their capacity is exceeded, free iron accumulates and leads to lipid peroxidation and cell damage . The 8 nerve is thought to be particularly susceptible because of its long glial segment as well as its contact with high flow cerebrospinal fluid in the pontine cistern . Common clinical findings include hearing loss, ataxia, and myelopathy . It is also associated with dementia and anosmia . The cause of the recurrent subarachnoid hemorrhages is not known in about 50% of cases .

There have been 8 reported cases of cochlear implantation in the setting of SS. Two of the cases reported by Wood et al had poor outcomes at 1 week and 6 months postimplantation. Of the other reported cases, the longest follow-up was 2 years. We reported on the successful functioning this patient achieved despite the apparent central source of hearing loss . Our optimism prevailed for a few years; however, she developed rapid decline after 6 years. Certainly, this could be accounted for by the progressive nature of the disease because her overall neurologic function has also declined.

The location of injury is felt to be predominantly retrocochlear. Audiometric data have been presented showing rollover and recruitment in a patient with SS, which suggests retrocochlear and cochlear impairment . Magnetic resonance imaging findings include hemosiderin deposition along cranial nerve VIII . Auditory brainstem response also have shown increased interval between waves I and V or isolated wave I . The evaluation of Ushio et al of vestibular evoked myogenic potentials with clicks and galvanic stimuli supports a retrolabyrinthine source of the vestibular dysfunction.

Despite the likely retrocochlear origin of the hearing loss, our patient initially did well. We remained optimistic for 5 years that her good performance would continue. Perhaps the cochlear implant was able to stimulate the remaining functioning neurons, until they too were damaged. There is no sufficient evidence to prove this.

More long-term experience would be useful to accurately counsel patients. Because the source and duration of hemosiderin deposition is not clear, the stability of the disease remains uncertain. With the published data to date, cochlear implantation in patients with SS is variable and may be of limited success based on the progression of disease.