Intervertebral disc extrusion / degenerative disc disease
Intervertebral disc disease is the most common neurological spinal disorder in dogs.
The intervertebral discs are situated between each spinal vertebra and act as a
cushion to provide strength and flexibility to the spine.
They have a semi-liquid centre called the nucleus pulposus, which is protected by
a fibrous outer layer (annulus fibrosus).
The term 'extrusion' (or herniation) means that the structure of the disc is damaged allowing the disc material to move and cause pressure on the spinal cord. This tends to occur in the thoracolumbar (low back) region and in the cervical (neck) region. There are 2 main ways in which the disc can herniate.
1. A healthy disc can rupture as a result of trauma such as a road traffic accident or a fall from height.
2. Degenerative disc disease
The majority of disc protrusions are secondary to underlying disc degeneration. This can occur in 2 ways:
Type I: Usually occurs in dogs 3 years and older with a peak in smaller dogs between 3 and 6 years old. It occurs because the nucleus loses its gelatinous nature and the disc becomes more cartilaginous. The annulus fibrosus tears allowing the nucleus to bulge out and put pressure on the spinal cord (disc extrusion). Common in chondrodystrophic breeds such as Dachshunds, Shi Tzu, and Pekingese. This process can start occurring as young as 2 months in affected breeds but signs usually show around 2 to 4 years of age. Symptoms will occur suddenly.
Type II: The discs lose their water and protein content and slowly become more fibrous. This causes progressive thickening of the outer layer of the disc, which presses up on the spinal cord (disc protrusion). This type of degeneration is more common in the regions of the spine that are particularly exposed to physical stress (the lower neck, mid-back and lower-back ) and is more common in older large-breed dogs. The signs are usually less severe and slower in onset compared to type I.
Symptoms and diagnosis
Spinal pain is the main symptom of disc disease. The dog may have the following signs
Low head carriage
A hunched back
Reluctant to move/exercise
Crying out when moving or being moved.
Neurological signs may also be present and will depend upon the location of the lesion. Symptoms can range from mild weakness, loss of coordination and ataxia to paralysis, faecal or urinary incontinence and loss of sensation in the legs.
Definite diagnosis is usually made using either CT (computed tomography) or MRI (magnetic resonance imaging). These tests can help confirm if there is a disc herniation, where it is and will also rule out other causes for the neurological signs.
Treatment depends on the location of the lesion and the severity of the symptoms. Where surgery is required an operation is performed to relieve the pressure on the spinal cord. Usually a slot in the vertebral bone is performed and then the disc material removed. The prognosis will depend on the severity of the symptoms and the time interval between onset and surgical decompression. The recovery rate is far more rapid in dogs that receive surgery within 48 hours of onset of symptoms.
In some cases dogs will respond to conservative management, although recurrence in the same area is quite common. Strict cage rest is required initially and drug management to reduce pain and inflammation.
Physiotherapy is essential in helping the recovery of normal movement patterns and function. Tailored neurorehabilitation techniques help to improve limb awareness, co-ordination, balance and strength. When appropriate hydrotherapy can be introduced and works well alongside land-based physiotherapy to promote strength and mobility and improve recovery.
Fibro-cartilaginous embolism (FCE)
Fibro cartilage is a substance found within the centre of the intervertebral discs (in the nucleus pulposus). Some how this substance makes its way in to the arterial system that supplies the spinal cord. The fragment causes the blood vessel to become blocked: an embolus. The portion of the spinal cord affected will die causing neurological defects. No one fully understands why this occurs.
Any dog can be a victim of FCE. About half those affected are giant breed dogs. Chondrodystrophic dogs (part of their normal breed conformation contains dwarf like features) such as Dachshunds and Basset Hounds are less susceptible because their disc material tends to calcify making it too hard to be involved. It is thought that miniature Schnauzers may have an increased risk because they tend to have excess fat levels and cholesterol circulating in their blood. FCE dogs tend to be young, between 3 and 6 years old and often present with FCE after some kind of exercise injury or trauma
Symptoms and diagnosis
The ischaemic damage to the spinal cord from the lack blood supply causes non-painful neurological damage. The symptoms come on very suddenly and are very variable depending on the location of the damage and the severity. There is a 50% chance that only the lumbar spine is affected, which means that only the hind limbs will be affected. Usually one side is worse than the other because the embolism is not a symmetrical event. The limbs may either have increased muscle tone and spasticity or decreased muscle tone and flaccidity. Your dog may not be able to use his back legs properly. The toes may knuckle under or he may not be able to use them at all. Many dogs are simply weak in the back legs and may or may not need help to get around. Occasionally all four limbs can be paralysed.
Diagnosis is based on clinical presentation and exclusion of other spinal cord injuries via myelogram or MRI.
Medications such as corticosteroids can be used to relieve spinal cord swelling and to prevent collateral damage. Surgery is not indicated in the treatment of FCE.
After your dog has received early medical management, intensive nursing care and physiotherapy are required. The goal is to maintain muscle tone while the spinal cord tissue heals. Most damage to the spinal cord occurs in the first 24 hours. After this the symptoms will not get worse. How well your dog recovers is very much dependent on how much loss of function there is to begin with. Early referral to physiotherapy and hydrotherapy is key and can help to improve movement, balance and strength