How can we better identify adult-onset neurodegenerative diseases in our patients?
Although many neurodegenerative diseases occur in dogs and cats, most of the well-described ones occur in neonatal or juvenile animals (e.g. cerebellar abiotrophies, most lysosomal storage diseases).1 In diagnosing adult-onset neurodegenerative disorders, two problems are seen. First, there may be a tendency to overdiagnose disorders such as degenerative myelopathy and canine cognitive dysfunction. This may occur because many owners of aged animals decline a full workup to avoid the anesthetic risk and are reluctant to intervene therapeutically in older animals. Because they choose not to intervene, owners more readily accept a diagnosis of a disease for which little can be done.
Second, practitioners may be uncomfortable diagnosing neurodegenerative disease in adult animals because relatively few adult-onset neurodegenerative disorders are well-described and, therefore, recognized by veterinarians. In the past, subtle changes in central nervous system (CNS) morphology were not identified on computed tomography images. The advent of magnetic resonance imaging (MRI) has changed this. During the next decade, new disease entities will be described.
When a neurodegenerative disease is suspected
1. Identify and document neurologic deficits.
2. Conduct a full diagnostic workup in all animals with progressive neurologic signs.
3. Stay informed of advances in veterinary neurology, particularly as MRI becomes more accessible in dogs and cats.
Which neurodegenerative diseases have an adult onset in dogs and cats?
Neurodegenerative diseases in dogs and cats can result from a wide variety of pathologic processes. These can be grouped as inherited disorders, in which an inborn defect causes progressive neuronal loss, and as acquired disorders that reflect an accumulation of environmental insults over time (Table 1).
Table 1. Adult-onset Neurodegenerative Diseases in Small Animals
The best-described inherited neurodegenerative diseases are the lysosomal storage diseases. Although most of these affect neonatal and juvenile animals, some storage diseases have a late onset. These include mucopolysaccharidosis type IIIB in Schipperkes and ceroid lipofuscinosis. The former disease causes progressive cerebellar signs in Schipperkes, first evident between 3 and 5 years of age.2 Because of the insidious nature of the signs, the animal may not be presented to a veterinarian until months after disease onset. Ceroid lipofuscinosis is a disease process distinct from the intraneuronal accumulation of lipofuscin that occurs with age.3 This storage disorder has been recognized in Tibetan terriers, English setters, cocker spaniels, dachshunds, and border collies, with sporadic reports in many other dog and cat breeds. Clinical signs usually develop in animals younger than 2 years old, but an onset of as late as 9 years of age has been reported, particularly in dachshunds.3 Signs usually reflect forebrain and retinal involvement, with changes in behavior and loss of night vision (nyctalopia) predominating. However, the changes have a diffuse distribution, and a wide range of signs have been reported including ataxia, paresis, head tremors, and seizures.