Congenital Vertebral Malformations
Malalignment and/or instability of spine resulting in spinal cord compression are/is caused by severe congenital vertebral malformations. The cause of malformations is unknown though it is strongly believed that the cause is genetic as certain types of malformation occur in specific dog breeds.
Types of congenital vertebral malformation
(i) Block vertebrae - resulting from fusion of two neighbouring vertebrae.
(ii) Butterfly vertebrae - resulting from a cleft in the vertebrae.
(iii) Hemivertebrae - wedge shape vertebrae.
(iv) Spina bifida - due to absence of vertebral arches or presence of a cleft in the middle of vertebral arch.
What signs do affected dogs show?
Dogs affected with congenital vertebral malformations usually do not show any obvious clinical signs. Signs that may be noticed include deviation of spine and progressive paralysis or wobbly gait caudal to the lesion in affected dogs under one year of age. The degree and presentation of clinical signs may vary according to the type of malformation.
(i) Block vertebrae - Clinical signs are usually not observed as the fusion of vertebrae is quite stable.
(ii) Butterfly vertebrae - Most commonly occurs in 'screw-tailed' breeds such as Boston Terriers, French Bulldogs and English Bulldogs. Condition is usually insignificant.
(iii) Hemivertebrae - Condition is seen in 'screw-tailed' breeds and usually involves thoracolumbar spine. The top, below or only one side of vertebra may be affected which causes differences in spine curvatures. Progressive paralysis and wobbly gait are also observed.
(iv) Spina bifida - Clinical signs observed depend on the affected site of spinal cord. Condition is also more commonly seen in 'screw-tailed' breeds and affects lower back spine.
How can the malformations be confirmed?
Puppies under one year of age showing signs of hind limb wobbliness and progressive paralysis must be suspected of having congenital vertebral malformations unless otherwise proven. X-ray can be taken to confirm the malformation.
(i) Block vertebrae - The malformations appear as fused vertebrae (i.e. one vertebra being the equivalent size as two of the dog's normal vertebrae) on plain X-ray.
(ii) Butterfly vertebrae - Vertebrae appear as 'butterfly' on plain X-ray when X-ray is taken with the dog lying on its back.
(iii) Hemivertebrae - Vertebrae appear as wedge shape, causing angulation of spine at affected area.
(iv) Spina bifida - Incomplete vertebral arches are seen in affected vertebrae when X-ray is taken with the dog lying on its back.
As no obvious clinical signs are seen in most congenital vertebral malformations, myelograms (X-ray taken after injection of a dye into spinal canal) are needed to interpret the effect of lesions seen on plain X-ray films. Myelographs may show signs of vertebrae causing compression to the spinal cord in block, butterfly and hemi-vertebrae. In the case of some forms of spina bifida, myelogram may show sac-like protrusion through the defect.
Can affected dogs be treated?
There is little to no treatment available for dogs with spina bifida. Surgical decompression and stablization can be performed on dogs with hemivertebrae having compression of spinal cord.
Dogs with spina bifida or significant neurological defects have poor prognosis whereas those with no observable clinical signs usually have good prognosis.