Richard A. LeCouteur, BVSc, PhD, DACVIM (Neurology), DECVN
A tentative diagnosis of type I disc protrusion or extrusion may be made on the basis of age, breed, history, and clinical signs; however, other causes of transverse myelopathy or apparent pain should be considered in the list of differential diagnoses.
Vertebral column radiographs and, in almost all cases, CSF analysis, are necessary to support a diagnosis of disc extrusion or protrusion, and to help eliminate other possible causes that may have similar presenting history and clinical signs. Care must be taken, however, in anesthetizing and positioning animals that have acute type I disc extrusions, as further extrusion of disc material and further spinal cord compression may occur with manipulation and movement of the vertebral column.
Mineralization of the nucleus pulposus is best seen on lateral radiographic views and usually is seen in one or more discs of most chondrodystrophoid dogs more than one year of age. Mineralized discs also may be seen in older non-chondrodystrophoid breeds of dog. Calcified material within the nucleus pulposus is indicative of disc degeneration, but alone is not of clinical significance.
The disc space of an extruded disc may be narrower than adjacent disc spaces and may be wedge-shaped with a decrease in the width of the disc space dorsally. However, positioning is important as some disc spaces (C7–T1, T9–10 or T10–11, and L7–SI) are normally narrower than adjacent spaces. "Spikes" of calcified material suggestive of disc extrusion may extend dorsally from a disc. Intervertebral foramina are larger in the lumbar spine, and calcified material often is easily visualized in the vertebral canal in this region. Disc material within the vertebral canal may appear as a hazy, indistinct shadow or as a dense mass with distinct margins.
Type II disc protrusion may be associated with narrowing of the disc space, osteophyte production, and end-plate sclerosis. Calcification of disc material rarely is seen in association with type II disc protrusion. In some animals with type I or type II disc herniation, obvious abnormalities are not seen on noncontrast vertebral radiographs.
Some combination of myelography, CT, myelography followed by CT, or MRI is almost always necessary to confirm that disc material has herniated into the vertebral canal, resulting in spinal cord compression. This is most important in determining the site (or sites) of disc herniation and in lateralization of disc material within the vertebral canal prior to surgical decompression.
Cerebrospinal fluid should be collected and analyzed at the time of myelography or advanced imaging procedures to rule out inflammatory or infectious disease of the spinal cord and/or meninges. Clinical signs in animals with GME, distemper myelitis, FIP, spinal lymphoma, and other disorders may mimic those of cervical or thoracolumbar disc disease, and such diseases may occur concurrently with intervertebral disc disease.
Type I Disc Extrusion
The appropriate treatment for animals with type I disc extrusion depends on an individual animal's neurologic status. The use of corticosteroids in dogs with type I disc extrusion is contraindicated in most cases and has been associated with pancreatitis, gastrointestinal bleeding, or colonic perforations.
Nonsurgical (medical or conservative) treatment may be recommended for animals with apparent pain only or animals that have mild neurologic deficits but are ambulatory and have not had previous clinical signs associated with disc disease. These animals should be strictly confined to a small area such as a hospital cage or a quiet place away from other pets for at least 3 weeks, and walked (on a leash or harness) only to urinate and defecate. The objective of confinement is to allow fissures in the annulus fibrosus to heal, thus preventing further extrusion of disc material, and allowing resolution of the inflammatory reaction caused by small amounts of extruded disc material.
Use of analgesic agents, muscle relaxants, or nonsteroidal antiinflammatory agents is not recommended in most cases, as it is believed that their use encourages animals to exercise and risk further disc extrusion. Very cautious use of analgesics or nonsteroidal antiinflammatory agents occasionally may be indicated; however, strict confinement followed by a period of restricted exercise is imperative. Owners should also be warned that an animal's neurologic status may deteriorate owing to extrusion of further disc material despite this treatment and to observe the animal very carefully. If the neurologic signs persist or neurologic status worsens, an animal's treatment should be reevaluated immediately. Owners should also be warned that a recurrence of clinical signs is common due to further disc extrusion at the same or a different site, and subsequent episodes may be more severe, especially in the thoracolumbar vertebral column.
Animals with severe cervical pain frequently do not respond to cage rest. These dogs often have large amounts of disc material within the vertebral canal, and dogs that do not show improvement after 7 to 10 days of confinement should be evaluated further by means of radiographs and myelography or advanced imaging, and ventral cervical decompression should be considered.
Surgical disc fenestration is recommended as a prophylactic measure to prevent further extrusion of disc material into the vertebral canal. Fenestration of the discs most likely to herniate (C2–3 through C6–7 in the cervical region and T11–12 through L3–4 in the thoracolumbar region) is recommended in animals that have had one or more episodes of apparent neck or back pain and have evidence of intervertebral disc disease on radiographs.
Animals with neurologic deficits such as paresis or paralysis with deep pain perception intact, animals with recurrent bouts of apparent back or neck pain, or animals with apparent back or neck pain (or mild neurologic deficits) that are unresponsive to strict confinement, should be evaluated by means of vertebral radiographs, CSF analysis, and myelography or advanced imaging. Surgical decompression of the spinal cord and removal of disc material from the vertebral canal should be strongly considered. Although many dogs with moderate or severe paresis improve neurologically if treated with cage rest, neurologic recovery is often more rapid and more complete in animals following surgical decompression of the spinal cord. In addition, the neurologic status of some dogs with type I disc extrusion, especially in the thoracolumbar vertebral column, suddenly worsens over a period of hours or days despite medical treatment. Such deterioration usually results from further disc extrusion that may result in irreversible spinal cord damage and permanent paralysis. This progression of signs always is a risk with medical treatment of animals with thoracolumbar disc disease. Progression is impossible to predict on the basis of history, clinical signs, or radiography. Owners should be made aware of treatment options and offered the opportunity of referral to an appropriate surgical facility when animals are initially presented.
Surgical treatment is not without risks. Anesthesia is necessary, and surgery occasionally results in further spinal cord damage due to surgical manipulation. Nonsurgical treatment should be attempted in animals that are poor anesthesia or surgical candidates or if surgical treatment is not possible financially.
In animals with clinical signs of a complete transverse myelopathy, without deep pain perception for a period of more than 24 hours, the prognosis for return of spinal cord function is poor despite medical or surgical treatment. Some of these animals may improve neurologically if given sufficient time; however, it is a matter of controversy whether surgical treatment increases the probability of improvement or not. In cases in which deep pain perception has been absent for less than 24 hours, the prognosis for return of spinal cord function is poor; however, surgical treatment may increase the likelihood of neurologic improvement in this group.
Regardless of whether medical or surgical treatment is instituted, animals that are paretic or paralyzed require intensive nursing care. Neurologic improvement may take weeks or months, and this requires owner cooperation and enthusiasm regarding care and physical therapy. Manual expression, intermittent catheterization, and/or indwelling catheterization of the bladder are often required to ensure emptying of the bladder. Weekly urinalysis, especially in animals that do not have voluntary control of micturition, is important in monitoring for urinary tract infection. It is also important to keep animals well padded, clean, and dry to prevent formation of pressure sores and to ensure that caloric and water intake is adequate. Physical therapy does not result in neurologic improvement but helps to prevent disuse muscle atrophy associated with paraplegia or tetraplegia. Physical therapy should not be attempted in animals treated medically for at least the first 2 weeks following onset of signs, as further extrusion of disc material may occur.
Type II Disc Protrusion
Treatment with corticosteroids may result in neurologic improvement for variable periods of time in animals with type II disc protrusion. The mechanism of action of the corticosteroids is unknown. However, corticosteroid therapy is not curative. In the thoracolumbar spine, surgical removal of protruded disc material may result in clinical improvement; however, the neurologic status of some dogs is worsened permanently despite careful surgical technique. The key to success in the medical management of type II disc protrusion is to change the lifestyle of the animal, avoiding all physical activity that may cause torsion of the vertebral column.
The use of acupuncture as a sole treatment of intervertebral disc extrusion in dogs is controversial. Acupuncture is an excellent adjunctive therapy in nonsurgical management of affected dogs.
Injection of the proteolytic enzyme chymopapain into the nucleus pulposus of intervertebral discs to cause discolysis has been used infrequently in veterinary medicine. Chemonucleolysis may also be useful as a prophylactic measure in animals with evidence of intervertebral disc degeneration to prevent acute type I disc extrusion. Chemonucleolysis is not indicated in cases of type I disc extrusion, as the enzyme is unable to reach sequestered nucleus pulposus within the vertebral canal.