There is an impressive group of hereditary, progressive cochleovestibular atrophies that are linked to degenerations of the nervous system. These were the subject of an authoritative review by Konigsmark and are summarized below. His clinical classification has been eclipsed by genetic findings but still serves as a useful guide. Such neurotologic syndromes must be set alongside a group of 5 diseases that affect the auditory and vestibular nerves exclusively: dominant progressive nerve deafness; dominant low-frequency hearing loss; dominant midfrequency hearing loss; sex-linked, early-onset neural deafness; and hereditary episodic vertigo and hearing loss. The last of these is of special interest to neurologists because both balance and hearing are affected.
It should be pointed out that in 70 percent of cases of hereditary deafness, there are no other somatic or neurologic abnormalities. To date, at least 3 separate autosomal mutations have been identified that are associated with a pure “nonsyndromic” type of hereditary deafness, the most common of which is in the connexin gene, as discussed in Chap. 14. A number of mitochondrial disorders have been associated with deafness alone as well as with a number of the better-characterized mitochondrial syndromes (see Chap. 34). The age of onset of hearing loss in the pure forms has been variable, extending well into adulthood.
Konigsmark has separated this overall category into 3 subgroups: patients with typical retinitis pigmentosa, those with Leber optic atrophy, and those with other retinal changes. With respect to retinitis pigmentosa, 4 syndromes are recognized in which retinitis pigmentosa appears in combination: with congenital hearing loss (Usher syndrome); with polyneuropathy (Refsum syndrome); with hypogonadism and obesity (Alstrom syndrome); and with dwarfism, mental retardation, premature senility, and photosensitive dermatitis (Cockayne syndrome).
Hereditary hearing loss with optic atrophy forms the core of 4 special syndromes: dominant optic atrophy, ataxia, muscle wasting, and progressive hearing loss (Sylvester disease); recessive optic atrophy, polyneuropathy, and neural hearing loss (Rosenberg-Chutorian syndrome); optic atrophy, hearing loss, and juvenile diabetes mellitus (Tunbridge-Paley syndrome); and opticocochleodentate degeneration with optic atrophy, hearing loss, quadriparesis, and developmental delay (Nyssenvan Bogaert syndrome).
Hearing loss has also been observed with other retinal changes, 2 of which are Norrie disease, with retinal malformation, hearing loss, and mental retardation (oculoacousticocerebral degeneration), and Small disease, with recessive hearing loss, mental retardation, narrowing of retinal vessels, and muscle atrophy. In the former, the infant is born blind, with a white vascularized retinal mass behind a clear lens; later the lens and cornea become opaque. The eyes are small, and the iris is atrophied. In the latter, the optic fundi shows tortuosity of vessels, telangiectases, and retinal detachment. The nature of the progressive generalized muscular weakness has not been ascertained.
Susac syndrome should be considered in the broad differential diagnosis of this group of disorders. This is a microvasculopathy that causes characteristic changes in the white matter of the cerebral hemispheres, retinal vasculopathy, and progressive deafness as discussed in
Chap. 34. The later onset and progressive nature of deafness in this and several other syndromes are distinguished from forms of congenital deafness that are typical of the group discussed below.
Hereditary Hearing Loss With Diseases of the Nervous System (See Table 14-1)