What Is Sensorineural Deafness
Causes of Sensorineural Deafness
Causes of Sensorineural Deafness
The cochlea may be damaged by rubella in the pregnant mother. Mumps, acute purulent meningitis, or chronic infection spreading from the middle to the inner ear may cause nerve deafness in childhood. Measles vaccination, mycoplasma pneumonic infection, and scarlet fever are in rare instances associated with acute deafness, with or without vestibular symptoms.
Sudden Unilateral Deafness
Little is known about the syndrome of sudden unilateral deafness without vertigo. Presumably it is of cochlear origin. A vascular causation has been postulated. on un-certain grounds. A few cases have complicated herpes zoster and mumps parotitis, but there is no proven relationship with the usual viral respiratory infections. In the remaining patients, recovery was much slower and often incomplete; in this latter group. the hearing loss was predominantly for high tones and was associated with varying degrees of vertigo and hypoactive caloric responses. Episodic deafness in one ear, without vertigo, proves in most instances to be
meniere disease .
High-tone sensorineural hearing loss
Explosions or intense, sustained noise in certain industrial settings or from gun blasts or even rock music may result in a high-tone sensorineural hearing loss. Certain antimicrobial drugs (viz., streptomycin, kanamycin, neo-mycin, and gentamicin) may damage cochlear hair cells. Quinine and acetylsalicylic acid may impair sensorineural function transiently. Otologists have described a progressive sensori-neural type of hearing loss as a late manifestation of congenital syphilis, allegedly occurring despite prior treat-ment of the latter disorder with adequate doses of penicillin. It has been claimed that the long-term administration of steroids may be useful in these circumstances. The pathologic basis of the hearing loss in such cases has not been determined, and the causal relationship to congenital syphilis remains to be established.
Auditory Nerve
The auditory nerve may be involved by tumors or by syphilitic or other types of chronic meningitis. Deafness may also result from a demyelinative plaque, infarction, or tumor involving the cochlear nerve fibers or nuclei in the brainstem. Rarely. deafness is the result of bilateral lesions of the temporal lobes. Pure word deafness is also due to temporal lobe disease. Here, despite normal pure tone perception and audiometry and normal brainstem auditory evoked potentials. spoken words cannot be understood.
Genetically determined syndromes
A large series of genetically determined syndromes which feature a neural or conductive type of deafness, some congenital and others having their onset in childhood or early adult life, have come to light (see articles by Konigsmark and by Proctor and Proctor). Most of them are inherited as an autosomal dominant trait, but others are characterized by a recessive or sex-linked transmission. There are few complete histo-pathologic studies of congenital and hereditary deafness. Two groups can be recognized aplasias and degenerations. Four types of inner ear aplasia have been described: (1) a complete absence of the otic capsule and eighth nerve; (2) an incomplete development of the bony and membranous labyrinths and the spiral ganglion; (3) a membranous cochleosaccular dysplasia with atrophy of the vestibular and cochlear nerves; and (4) rare chromosomal aberrations (trisomies) characterized by abnormality of the end organ and absence of the spiral ganglion.
Other developmental and heredodegenerative syndromes
In addition to these more or less pure aplasias of the auditory system, cochlea-vestibular atrophies and degenerations occur as part of many other developmental and heredodegenerative syndromes. integumentary abnormalities such as hyperkeratosis,
vertigo, hyperplasia or scantiness of eyebrows, albinism, large hyperpigmented or hypopigmented areas, brittle twisted hairs, and coniform and missing teeth; ocular abnormalities such as hypertelorism, severe myopia, optic atrophy. congenital and juvenile cataracts, and retinitis pigmentosa: neurologic abnormalities such as polyneuropathy and sensory ataxia (Refsum syndrome), progressive ophthalmople-gia and cerebellar ataxia, bilateral acoustic neuromas, photomyoclonic seizures, and mental deficiency; skeletal abnormalities; and renal, thyroid, or cardiac abnormalities.
by: Emma Parker
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