Inherited cerebellar degenerative disorders with an adult onset have been described in American Staffordshire terriers4 and related American pit bull terriers as well as Brittany spaniels.5 In these breeds, an onset of cerebellar and vestibular signs (e.g. hypermetria, ataxia, nystagmus) occurs around 4 to 6 years of age. The signs are slowly progressive, and as a result, affected
animals may be presented to their veterinarians late in life. Other breeds with inherited cerebellar degeneration that can
present in adulthood include Gordon setters,6 Old English sheepdogs,7 and Scottish terriers.8 In these breeds, however, signs usually first appear when the animal is still a juvenile (6 to 18 months).
Breed-related disorders suspected to be inherited
The next group of diseases includes those thought to be inherited because of an established breed predisposition but for which
a mode of inheritance has not been determined. The best known of these is degenerative myelopathy. This disease is well-described
in German shepherds and occurs sporadically in other large breeds.9 It appears to be an emerging problem in Pembroke Welsh corgis, boxers, and Rhodesian ridgebacks, although these breeds may
be suffering from a different degenerative disease process than that seen in German shepherds. Degenerative myelopathy causes
progressive paraparesis in dogs older than 5 years of age. Usually the affected dogs are 9 years or older.
There are isolated reports of rare breed-related neurodegenerative diseases in dogs with an onset of signs well into adulthood.
Rottweilers suffer from several breed-related neurodegenerative diseases, but the only one with a true adult onset of signs
is leukoencephalomyelopathy.10 Progressive signs of ataxia, hypermetria, and tetraparesis appear between 1 and 4 years of age and are slowly progressive.
In addition, neuroaxonal dystrophy in rottweilers11 usually results in signs of tetraparesis before 1 year of age; however, because the signs progress slowly over a number of
years, this disease should also be considered in adult rottweilers. A necrotizing encephalopathy that has been likened to
the human mitochondrial disorder known as Leigh's disease has been reported in five Alaskan huskies.12 In four of the affected dogs, an acute onset of ataxia, seizures, behavioral changes, and signs of cranial nerve deficits
occurred before 1 year of age; however, in one dog the signs did not appear until 2.5 years of age.
Peripheral neuropathies characterized by degenerative changes may occur in older dogs.13 These include dancing Doberman disease, a degenerative neuropathy that affects the pelvic limbs of adult Doberman pinschers
causing flexion of the limbs and a repeated shifting of weight, which give the appearance of dancing. This disease has a reported
onset of signs as late as 7 years. Adult-onset polyneuropathies in Leonbergers, rottweilers, and Great Danes also cause generalized
weakness.
Acquired diseases
The degenerative neuropathy associated with diabetes is well-recognized in cats and probably occurs subclinically in dogs.
Insulinomas also cause a degenerative neuropathy in dogs, and hypothyroidism can cause generalized weakness due to a neuropathy.
Dysautonomia refers to a degenerative disease of the autonomic nervous system in dogs and cats that usually affects adult
animals.14 Progressive loss of autonomic neurons causes a wide variety of debilitating autonomic signs, including mydriasis, keratoconjunctivitis
sicca, regurgitation, urinary retention, constipation, and diarrhea; it is often fatal. Many theories exist about the cause,
but increasing evidence suggests that, at least in cats, this disease is the result of Clostridium botulinum C toxin.15
Other disorders
Cognitive dysfunction
The less well characterized diseases are those that seem to be related to aging itself. All companion-animal veterinarians
are familiar with an older dog or cat that, according to the owner, appears to have become senile. Signs can include a loss
of hearing and vision, getting lost in familiar environments, a loss of housetraining, constant pacing, and a change in sleep
patterns. In dogs, this aging syndrome has been called canine cognitive dysfunction, although many neurologists and behaviorists are still uncomfortable with the actual definition of the disease and what it
encompasses.16
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