34th Annual Scientific Meeting proceedings

Congenital spinal deformities have been recognized for many years, and with the recent surge in popularity of French bulldogs (FRBL), the frequency with which we see these cases has increased.  Congenital spinal deformities can include congenital vertebral malformations (CVM), caudal articular process dysplasia, transitional vertebrae, spinal bifida, to name a few.  This session will focus on the CVMs seen commonly in the French and English bulldog.

Though initially recognized screw-tailed breeds, including French bulldogs, English bulldogs, Pugs, it has been recognized that the Pug should not be grouped with the bulldogs due to genetic differences.  The frequency of congenital vertebral malformations (CVMs) is much greater in the French bulldog than Pugs and English bulldogs, reported as high as 100%, with many having no clinical significance. Interestingly, Pugs with an identified hemivertebrae are 10 times more likely to have neurological signs compared to FRBLs and English bulldogs with hemivertebrae. 

The presence of malformations is not necessarily a concern. Up to 75% of English bulldogs and 95% of FRBLs will have clinically insignificant CVMs.  Interestingly, multiple malformations have a lower likelihood of causing clinical signs than a single malformation.  CVMs occur with highest frequency from T5-T9 with a ventral wedge shape being the most common malformation. There is solid evidence that a kyphotic Cobb angle >35° increases the likelihood of neurological signs. Interestingly, scoliosis is virtually never a cause of myelopathy in dogs.  Most commonly, dogs less than 1 year of age will display signs of a slowly progressive, non-painful T3-L3 myelopathy if a CVM is the cause.

Diagnosis can be complex.  Identification of a CVM is often straightforward and can be done with radiographs.  Magnetic resonance imaging is often required for identification of spinal cord compression or other concurrent pathology.  Computed tomography is best for bony definition, can be crucial for surgical planning, and can be insufficient for assessment of spinal cord compression or parenchymal pathology. 

Treatment of CVMs is difficult and currently there is no definitive treatment recommendation. It has been suggested that minimally affected young dogs could clinically stabilize when they reach skeletal maturity, but a more recent study showed that medical management results in progression and a poor outcome in all cases. 

Initial surgical interventions for CVMs included decompression and stabilization.  It is becoming increasingly evident that decompression is not always necessary, indicating that spinal canal stenosis or spinal cord compression is not a significant factor in this condition.  There is also the concern that removal of bone in the area of a malformation could exacerbate the suspected or present vertebral instability.  Multiple studies have shown clinical improvements in dogs with CVMs that received stabilization alone, suggesting that instability may be the cause of myelopathic signs. A few studies have been published describing reduction of the malformation or partial realignment of the spine. These studies have shown positive outcomes and have also inherently included vertebral stabilization.  Though it seems stabilization of clinically significant CVMs is likely to result in a successful outcome, the role of correction or reduction of the malformation is unclear.

Based on the current body of knowledge surrounding CVMs, I recommend surgical intervention in young dogs, typically less than 3 years of age.  Considering that FRBLs and English bulldogs both suffer from brachycephalic obstructive airway syndrome, my management recommendations often include airway evaluation +/- surgery prior to advanced imaging or neurosurgery. My institution has a recommended protocol for management of these cases with the aim of reducing potential complications. 

Once deemed stable for general anesthesia and recovery, I recommend CT and/or MRI.  For the <9 month old FRBL or English bulldog, CT is often my first choice of imaging modality.  Neurologic status does play into my choice of imaging modality with more severely affected dogs being more likely to have an MRI as well as a CT. 

Some form of stabilization is generally my surgical recommendation in the young dog with no other spinal pathology. Depending on the malformation and the integrity of the adjacent vertebrae, stabilization with implants (pedicle screw and rod system or pins and polymethyl methacrylate) or an in-situ biofusion are the two techniques I am most likely to recommend. 

Considering the frequency of CVMs, intervertebral disc extrusions (IVDE), and spinal only meningoencephalitis of unknown etiology (MUE) in French bulldogs, it is critically important to identify the correct causative pathology prior to making a treatment plan.  The juvenile FRBL with a non-painful, chronic, progressive T3-L3 myelopathy is likely to have clinical signs due to a CVM.  The young adult FRBL with an acute to peracute onset of a painful T3-L3 or L4-S3 myelopathy is much more likely to be suffering from IVDE. The young adult to adult FRBL with a subacute to chronic, non-painful T3-L3 myelopathy has a higher likelihood of having spinal only MUE as a cause of their signs.  Correlating the neuroanatomic localization with the identified lesion is the first step, and the second step is deciding if the history and progression fit with the identified lesion.