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Sudden unilateral deafness usually suggests a cochlear impairment but a brainstem stroke should also be evoked especially when brainstem signs are associated. Deafness with brainstem infarct was described many years ago1 but bilateral deafness has been very rarely reported2-4 and would have a poor prognosis.3 We report a case of lateral inferior pontine infarct disclosed by bilateral deafness with a favourable course.
A 74 year old man with diabetes mellitus and auricular fibrillation regularised for two years, suddenly experienced a right deafness associated with vertigo and gait disorder. Three days later, deafness became bilateral. Clinical examination showed a major bilateral cerebellar ataxia and dysmetria without tinnitus, facial palsy, lateral gaze paresis, Horner syndrome, tactile, or motor disorder. Hearing loss was severe and prominent in the right ear. Neuropsychological examination was normal, especially oral expression, naming, and lecture. Tonal audiometry showed a sensory deafness on the left (60 to 80 dB loss) and a mixed deafness on the right (80 to 120 dB loss) with a prominent sensory component. Brain MRI disclosed a left inferior pontine infarction extending to the territory of the left anterior inferior cerebellar artery (AICA, figure). No lesion was found on the right side. Brainstem auditory evoked potentials (BAEPs) showed poorly synchronised responses with mildly delayed latencies of waves I (right 1.92 ms; left 1.96 ms) ; waves II to V were not recorded. Middle latency auditory evoked potentials were normal (right Na 19.4 ms, Pa 31 ms; left Na 20.1 ms, Pa 29.8 ms) demonstrating the sparing of higher auditory pathways. This pattern indicated a bilateral retrocochlear impairment. Echocardiography, ECG, and Holter-ECG were normal. Doppler sonography showed a stenosis of the left carotid artery of about 60%. Medical history, clinical picture, and the infarct location suggested that atherosclerosis of the basilar artery was the cause of stroke. The long term course showed a clear improvement and 10 months later, an important right hearing loss (50 to 70 dB) and a mild left hearing loss (10 to 30 dB) still persisted but allowed good intelligibility. Word repetition and environmental noise recognition were quite good. Nevertheless, some difficulties to localise sound persisted with systematic search to the left side.
According to Adams,5 deafness characterises the lateral form of inferior pontine infarct and is usually due to an infarction of the cochlear nucleus or auditory nerve. In the present case, the delayed latency of wave I supports the sparing of the distal part of the auditory nerves and the absence of waves II to V shows that deafness resulted from a bilateral cochlear nuclei or proximal auditory nerve impairment.6 The finding of a left inferior pontine infarct clearly supports this interpretation for the left deafness. On the right side, no lesion was found but the BAEP pattern strongly suggests a lesion within the same area. The right deafness is likely to be due to a lesion of the radicular portion of the auditory nerve, which is supplied by the auditory artery (branch of the anterior inferior cerebellar artery), or by a small pontine infarct even if it was not visualised on MRI.7
Sudden deafness due to a brainstem infarct could be underdiagnosed and we should look for this possibility using MRI and BAEP examination, especially in patients with risk factors for stroke and presenting with other neurological signs. This case also suggests that the deafness outcome may be favourable.