3.4 NEUROLOGICAL DISEASES OF OLD AGE CHRONIC 'OLD DOG' ENCEPHALITIS SPINAL DISEASE
There are several diseases that may involve the spinal canal producing clinical signs including neurological deficits and these need to be differRadiography is important in reaching an accurate diagnosis and myelography is usually needed to identify space occupying lesions. Aniwith gait abnormalities should also have non-neurological causes eliminated including osteoarthritis (or degenerative joint disease), hip dysplasia, bilateral osteochondritis dessicans and generalised bone dise.g. renal secondary hyperparathyroidism.



Discospondylitis

Discospondylitis may occur at any age and occurs most frequently in the cervical spine or at the lumbosacral junction. It is an inflammatory process (usually secondary to bacterial infection) of the intervertebral disc space which extends into the vertebral bodies either side and encroaches on the spinal canal. The diagnosis is confirmed by radiology and it needs to be differentiated from spondylosis which is a common incidental radiofinding in older dogs.

Cervical spondylopathy usually occurs in an earlier age (up to 7 years in Dobermans).



Degenerative disc disease

Degenerative disc disease is common in young chondrodystrophic dogs and clinical signs associated with disc degeneration are unusual in geriatric patients of these breeds. In other large breed dogs the condition is more likely to be seen in middle-aged or older animals and they usually present with a gradually progressive hindleg ataxia and paresis. Anti-inflammatory drugs are the treatment oT choice, and surgery is less likely to be successful in these patients than in young animals with acute disc prolapse. Somethere is a concurrent degenerative myelopathy.



Chronic degenerative radiculomyopathy

Most central and peripheral myopathies occur in young animals, but chronic degenerative radiculomyelopathy (CDRM) is frequenfly seen in elderly male German shepherd dogs and it is occasionally seen in other breeds. There is degeneration of the lumbar dorsal columns, fasciculus gracilis, lateral corticospinal tract and around the ventromedian fissure of the white matter of the cord. Lesions also involve the dorsal spinal roots and the thoracolumbar grey matter and nucleus gracilis show asytrocytic sclerosis. These degenerative changes are typical of a 'dying-back' disease (Griffiths and Duncan 1975).

The cause is unknown although vitamin B12 (cobalamin) deficiency has been suggested by some workers.

Diagnosis is based upon the presenting clinical signs (Table 3.10) and absence of a space occupying spinal lesion on myelography. Treatment is symptomatic, for example the provision of boots to protect the dorsa of the feet and there is no treatment that can reverse the neurological deficit.


Lumbosacral spondylopathy

There are a number of pathological changes that may occur at the lumjunction leading to signs of low back pain or hyperaesthesia with decreased ability to exercise, difficulty in rising, and sometimes faecal or urinary incontinence. The signs are usually bilateral and weak hock flexion is the main neurological deficit (Denny et al. 1982). Large breed working dogs are most often affected though a similar condition has been reported in smaller toy breeds.

The aetiopathogenesis may be due to spinal stenosis, disc protrusion, spondylosis deformans or discospondylitis. Myelography, epidurography, transosseus venography or CT scan are useful for differentiating the cause and electrophysiological testing (EMG) is also helpful.

Decompressive surgical treatment (dorsal laminectomy or foris reported to provide good success, and antibiotic treatment is required for discospondylitis.