Disc Herniation in Dogs
VETERINARIAN SPECIALTY CASE STUDY
“The Case of Presumptive Pug Encephalitis”
Failing prednisone therapy leads to a thorough neurological exam, radiographs, an MRI, and a potential spinal tap, revealing disc herniation and a synovial cyst at the root of a pug’s problem.
“Kwazee” is a 9 year old MN Pug who was referred to ASG for further evaluation of presumptive Pug encephalitis which was failing prednisone therapy. Kwazee had initially been seen by his general veterinarian three months prior for a subdued demeanor and gait deficits in all four limbs. Because of the abnormal demeanor and generalized ataxia, Pug encephalitis was suspected. His neurologic symptoms improved with prednisone but worsened while he was still taking the medication. CBC, chemistry panel, and urinalysis were normal. Kwazee also had a previous history of unexplained right thoracic limb “lameness” that would intermittently appear and resolve spontaneously.
Kwazee was quiet and shy during his examination but appeared mentally normal. He exhibited a short-strided, choppy gait in the thoracic limbs and a weak, ataxic gait in the pelvic limbs. Moderate cervical pain was noted, and this was thought to be the cause of the previously-observed subdued demeanor. The remainder of the neurologic exam was normal, including cranial nerve exam. Neurolocalization was to the low cervical spinal cord, from C6-T2. His symptoms and history were thought to be most compatible with intervertebral disc disease, but myelitis/encephalitis, spinal anomaly and spinal tumor were also thought to be possible. It is very unusual for Pug encephalitis to affect the low cervical spinal cord.
Cervical spinal and chest radiographs were unremarkable. A cervical spinal MRI was recommended, along with a spinal tap if necessary. The MRI revealed degenerated discs at C5-6 and C6-7, with a disc herniation at C6-7 causing significant spinal cord compression. Additionally, a fluid-filled structure was noted just medial to the right articular facet at C3-4. The structure was in contact with the spinal cord but was causing minimal to no spinal cord compression. A spinal tap was not performed, because the imaging results perfectly explained the dog’s symptoms.
Disc herniation at C6-7, right synovial cyst at C3-4.
A ventral slot was performed at C6-7 and a large amount of herniated disc material was removed from the spinal canal. Kwazee returned to normal within 2 weeks of surgery.
Sometimes it can be hard to separate the wheat from the chaff with neurology cases. Kwazee’s initial presumptive diagnosis of Pug encephalitis was made based on the subdued mental status and generalized ataxia. However, upon questioning his owners, we learned that all along his gait had been characterized by a stiffness and choppiness in the thoracic limbs. That finding puts the lesion localization squarely into the C6-T2 region of the spinal cord and we know from managing many cases of Pug encephalitis over the years that the spinal cord is rarely affected by this disease. Once we found that Kwazee’s neck was painful, it began to seem most likely that his quiet demeanor related more to neck pain than brain pathology.
But what about the synovial cyst? Why not address that surgically while we were in there? Well, firstly, the disc would require a ventral surgical approach whereas the synovial cyst would require a dorsal approach- ie, two completely separate surgeries, twice the anesthesia time and an exponentially more difficult post-op recovery for Kwazee because both the ventral and dorsal neck muscles would be dissected during surgery. Secondly, a synovial cyst is a developmental disease and it is likely the cyst had been present since Kwazee was a young adult. Yet his current symptoms had been present for only 3 months, making it much more likely that disc herniation was the cause of the current symptoms and the synovial cyst was the cause of the sporadic right thoracic limb deficits that the owner considered to be of minimal consequence for Kwazee.
And finally, why no spinal tap? How can we be sure the Pug encephalitis is not present if we don’t perform a spinal tap. Well, honestly, we can’t be 100% sure. But we don’t like to run tests that add unnecessary risk and expense for our patients and we went into the MRI knowing a disc herniation was our top rule-out. Then we found a disc herniation in the exact place in the spine that our neurologic exam predicted the lesion would be, so we could feel very confident that the MRI alone was sufficient to make the diagnosis in Kwazee’s case.
At ASG, we have the luxury of our neurologist being present to review the images while the patient is still under anesthesia, and we take advantage of that to minimize performing more tests than we need to achieve the diagnosis. It can be a great challenge in veterinary medicine to select just the tests you need to establish the correct diagnosis, no more and no less. In Kwazee’s case we are so glad that his problem turned out to be more straightforward than originally suspected and that he was able to make a complete recovery.
It can be a great challenge in veterinary medicine to select just the tests you need to establish the correct diagnosis, no more and no less. In Kwazee’s case we are so glad that his problem turned out to be more straightforward than originally suspected and that he was able to make a complete recovery.
by Stacey Sullivan, DVM
Diplomate American College of Veterinary Internal Medicine (Neurology)
*Photo of Pug is not “Kwazee.”