By Jay McDonnell, DVM, MS, Diplomate ACVIM (Neurology)
The most common neurosurgical cases for dogs are those of the thoracolumbar (T3-L3) spine, the cervical-cervicothoracic (C1-T2) spine and intracranial surgery. Knowing when to refer your neurosurgical cases can be the most artful of the art and science of veterinary medicine.
We wish to provide our patients with the best options for a successful outcome, while not needlessly running unwarranted and potentially dangerous tests.
The most common questions I receive about these types of cases from veterinarians in general practice are:
1. When should I refer?
2. What should I do prior to referral?
3. If the owner declines a referral, what recommendations should I provide for the pet and the owner?
Please keep in mind that, as I attempt to answer these questions, it is with the understanding that all cases are not the same and I can only provide general guidelines for the “typical case.”
The Thoracolumbar Disk Dog
The dog with intervertebral disk disease (IVDD) in the T3-L3 spine is one of the most common neurosurgical emergencies in veterinary medicine.
- The Hansen’s Type I intervertebral disk abnormality is seen in chondrodystrophic dog breeds (e.g. Dachshund, Cocker Spaniel, Basset Hound, Beagle, Pekingese and Poodle) that have chondroid metaplasia of their disks (nucleus pulposus) that begins early in life. These disks usually extrude causing acute, sometimes catastrophic, clinical signs of paralysis.
- The other type IVDD is called Hansen’s Type II disk and is seen most commonly in older, larger, non-chondrodystrophoid dogs with fibroid metaplasia of the disk. These disks usually protrude (bulge) rather than extrude. The dogs with Type II IVDD progress slowly with less pain and discomfort, generally.
Clinical signs of IVDD include spinal pain and varying degrees of neurologic deficits. Spinal pain without paresis may cause the animal to be agitated, aggressive or more vocal. Some animals will lay quietly refusing to walk, whereas others will walk constantly or pace. Thoracolumbar IVDD may cause animals to walk with an arched back. Some animals will have spinal pain as their only clinical sign.
Spinal pain in patients may improve, remain static or progress, depending on the disease progression and management strategies. The early signs of IVDD can often be managed conservatively (cage rest and non-steroidal anti-inflammatory drugs). Improper management of the dog with spinal pain and no other neurologic deficits may result in progression of the clinical signs.
Progression of neurologic signs is correlated with increasing compression of the spinal cord. Clinical signs progress in the following order: spinal pain, ataxia, paresis, paralysis and loss of deep pain sensation.
- Ataxia is the loss of coordination and is characterized by a broad-based stance and incoordination of the trunk or limbs in IVDD. Clinically we may see crossing over of the limbs when walking or an over-reaching gait. Postural reactions may be diminished or absent with an ataxic animal.
- Paresis (weakness) and paralysis are measures of an animal’s voluntary motor ability. Gradation is arbitrary and may be characterized as mild, moderate or severe. It is more helpful to describe if the animal can support weight or advance the limbs. The ability to perceive superficial pain is typically lost at the same time that voluntary motor control is lost.
- The perception of deep pain is the last modality lost. An animal with no deep pain may retract its leg reflexively but does not cry out, attempt to bite the examiner or move away from the stimuli. An animal that has lost deep pain perception has a guarded prognosis and, for the best possible outcome, should be considered an emergency surgical candidate. Deep pain sensation is cerebral recognition of the painful stimuli and is different from the flexor reflex.
A presumptive diagnosis of IVDD may be made with compatible history and examination in a typical breed. Radiographs are not made if medical therapy is being contemplated unless there is suspicion that another disease such as discospondylitis, vertebral tumor or trauma is present. Radiographs ideally should be performed under anesthesia or heavy sedation with the x-ray beam centered on the probable lesion site as determined by the neurologic exam. The spine must be straight with little or no rotation.
Radiographic findings suggestive of IVDD include: collapse or wedging of the intervertebral disk, deformities of the intervertebral foramina, radiopaque material in or around the spinal canal and a decrease in the articular joint space.
Diagnosis of spinal cord compression caused by IVDD requires imaging of the spinal cord with computed tomography (CT) or magnetic resonance imaging (MRI). All of these methods require general anesthesia and the animal may need to be transported to a referral facility.
Treating, Managing and Prognosticating IVDD
There is a diversity of opinion regarding treatment options for dogs with IVDD, but general guidelines can be used for selecting therapy. I’ve included my system for grading compressive spinal cord disease, which may be useful in determining treatment options. Decisions regarding when and if surgical versus medical treatment for spinal compressive disease is indicated depend primarily upon the severity of the neurological signs and the chronicity of the problem. In addition, treatment is modified in relation to the presumptive diagnosis, owner finances, and concomitant medical problems.
GRADES 1 & 2: Dogs that are in pain only (Grade 1) or that have very mild weakness and pain (Grade 2) may be treated with cage confinement, nonsteroidal anti-inflammatory drugs (NSAIDs) and pain medications (Tramadol 1-2 mg/kg every 6-12 hours) for two to four weeks. Cage confinement means using a small airline crate placed in a quiet room where there is no disturbance.
- If an animal is still painful with NSAID treatment, I recommend muscle relaxants such as methocarbamol (Robaxin), 10-20 mg/kg PO TID or diazepam, 2-5 mg PO TID for several days.
- Pain medications such as tramadol, 2-3 mg/kg PO TID-QID or codeine, 1-2 mg/kg PO TID-QID can be utilized.
Hospitalization of these dogs accomplishes three goals for the clinician: You ensure the dog is rested properly; you can closely monitor your patient for progression; and you can show your client that medical management can work successfully.
- If clinical signs are not improved after two weeks or the dog worsens, definitive diagnosis and surgery should be considered.
- If the dog improves with cage confinement, continued treatment is indicated for two weeks after the animal is clinically normal.
- Conservative medical treatment should be recommended only if the clinician has great confidence in a presumptive diagnosis of IVDD or a client declines definitive diagnosis and treatment.
- In the case of an older patient or one that is clinically ill (e.g. anorexia, weight loss, fever, etc.), a more aggressive diagnostic course of action is warranted.
GRADES 3-6: These animals are surgical candidates.
- Grade 3 motor dysfunction refers to an animal that still has movement but cannot bear significant weight or propel themselves on their own.
- Animals with Grade 4 neurological dysfunction have no motor, are completely paralyzed but still have sensation of deep pain perception (see Fig X(Bailey)). If these animals have surgery performed have an excellent recovery rate (90-95%).
- Grade 5 animals (those that have lost the perception of deep pain for less than 48 hours) that are operated on still have a fair to good prognosis for recovery (60-80%).
- If an animal has lost deep pain for more than 48 hours (Grade 6), a guarded prognosis should be given to the owner, although recent reviews indicate a 50% recovery rate.
Animals in the Grade 5 and 6 categories may require an emergency myelogram if the preferred imaging modalities of CT or MRI are not available in a timely manner prior to surgery in order to definitively diagnose and localize the ruptured disk.
Steroids and Intervertebral Disk Disease
Corticosteroid therapy is controversial in treating IVDD. There is no broad consensus for treating dogs with these drugs.
My opinion is not to give steroids for IVDD for two reasons: Steroids have never been shown to be efficacious for compressive spinal cord injury in dogs or humans; and steroids can cause serious (even fatal) side-effects.
If steroids are given, only dogs that are Grade 5-6 should receive them; they should be given within the first 8 hours of clinical signs and steroids should not be continued past the first 24 hours, as the risk of gastrointestinal complications increases with longer therapy. Methyl-prednisone sodium succinate (SoluMedrol) is given IV over 15 minutes. The following protocol has been advocated to be used within 8 hours if spinal cord trauma is suspected.
- 30 mg/kg at time 0
- 15 mg/kg at time 2 hours
- 7.5 mg/kg at time 6 hours
- then 7.5 mg/kg every 6 hours for 24 hours
Alternatively, a CRI can be given following the initial dose at a rate of 2.5 mg/kg/hr.
The risk of GI ulceration increases greatly with concurrent steroidal and NSAID use; this is not recommended.
When to Refer
In dogs suspected with thoracolumbar IVDD, referral is indicated for dogs that cannot walk or those that do not respond to proper medical management.