Eighth cranial nerve dysfunction in hyperostosis cranialis interna.

Hyperostosis cranialis interna is a recently described autosomal dominant bone disorder characterised by hyperostosis and osteosclerosis confined to the skull, especially the calvarium and the skull base. In the affected family members, we found variable simultaneous involvement of cranial nerves I, II, VII and VIII from late childhood onwards, most likely due to nerve entrapment. Auditory and vestibular functions were followed in 3 young family members for 8 years. At the first examination, pure tone audiograms were normal in all 3 cases and case 1 showed no caloric response in the right ear. During follow-up, this ear developed severe hearing loss progressing to deafness. The left ear showed transient sensorineural hearing loss and a temporarily diminished caloric response. Similar observations were made in case 2. Both cases showed abnormal brain stem auditory-evoked responses during and after the sudden hearing loss, in which initially only wave I was preserved and later on wave V returned with significantly prolonged I-V interval. The latter phenomenon was also observed in case 3 on both sides in the presence of normal audiograms during and after transient unilateral facial nerve paralysis, which was accompanied by bilateral diminished caloric responses.