Neuro-otological syndromes for the neurologist

Neurologists may be tempted to regard deafness as “somebody else’s problem”—generally the cause will lie within the remit of an ear, nose, and throat (ENT) specialist. While such an approach is often reasonable, there are a number of circumstances in which knowledge of deafness and the syndromes with which it can be associated can take on real importance. Neurologists need to structure their thinking about loss of hearing and be aware of the neurological syndromes that may present with deafness as a component. The complaint can thus be used as “part of the puzzle” when constructing a differential diagnosis in the neurology clinic, and acknowledged and referred to an ENT colleague when the problem is non-neurological.

CAUSES OF HEARING LOSS

Hearing is the result of complex processes involving the structure of the ear, the function of the inner ear and vestibulum, and the function of the auditory nerve. Peripheral hearing loss can be divided into two main categories, which may co-exist in the same patient. Conductive hearing loss is caused by failure of sound conduction from the environment to the inner ear, and is usually due to problems in the external ear, eardrum, tympanic membrane or middle ear. Common causes include malformations, middle ear infections, trauma causing disruption of the eardrum or middle ear, and stiffness of the eardrum or middle ear bones (otosclerosis). Sensorineural hearing loss (SNHL) is the result of disorders of the inner sensory apparatus. It can be caused by problems in the inner ear, cochlea, auditory nerve, or auditory nerve nucleus. Although some “neurological” diseases are associated with conductive hearing loss, generally neurological causes are sensorineural.

Peripheral neurological causes of SNHL are listed in table 1. The text and tables that follow expand on the categories in table 1, highlighting particularly the syndromic diseases and patterns that can include hearing …