Spina bifida is a congenital disorder characterized by defective embryonic development of one or more vertebrae. Vertebrae are the bones in the back and neck that support the body and provide a protective corridor through which the spinal cord passes. Collectively, the vertebrae are referred to as the spine or the spinal column.
Some basic anatomy may be helpful to understand what spina bifida is and why it affects dogs the way that it does. Each individual vertebra is made up of several distinct bony parts. The vertebral body is the bottom-most (ventral) part of an individual vertebral bone. It is cylindrical in shape and separated from the vertebral bodies in front and behind by disks made of cartilage and fibrous tissue. The vertebral bodies and associated intervertebral disks function as shock-absorbers. A semicircular vertebral arch rises from the top (dorsal) side of each vertebral body, surrounding, enclosing and protecting the spinal cord. Several paired bony projections (the dorsal spinous processes) grow upward from the vertebral arch and normally form connections with the ribs and with the dorsal spinous processes of vertebrae in front and behind. It is this anatomical system that allows the spine to bend and flex.
Spina bifida occurs when the two halves of one or more vertebral arches do not fuse normally during prenatal development. When this happens, the spinal cord may or may not squeeze out through the resulting gap in the bone. The defect can occur anywhere along the spine. However, the vertebrae at the base of the spine – in what are known as the caudal lumbar and lumbosacral areas - are most commonly affected in domestic dogs.
Causes of Spina Bifida
The causes of spina bifida in domestic dogs are unknown. Because the condition occurs with more frequency in certain breeds (e.g., Bulldogs and Manx cats), a genetic component is highly likely. Ingestion by a pregnant bitch of substances that are known to cause birth defects (teratogenic compounds), malnutrition during pregnancy and possible environmental conditions are also reported to be contributing factors. It is clear that spina bifida develops in utero and is an abnormality of embryonic development that is present in affected puppies at birth. Most authorities believe that the causes of spina bifida are multifactorial.
Prevention of Spina Bifida
Because the causes of spina bifida are not well-understood, there is no meaningful way to describe an appropriate prevention protocol. Of course, pregnant bitches should be fed a high-quality diet and kept away from potential toxic substances.
Spina bifida is the most common ailment in a medical complex referred to as spinal dysraphism. Dysraphism is the defective fusion of parts that normally unite. Dogs with spina bifida have defective or nonexistent fusion of the top (dorsal) parts of one or more of the bones in their spine.
By definition, spina bifida is a congenital disorder, meaning that it is present at birth. Spina bifida is not progressive and does not worsen with time. Signs of this condition usually are first noticed when affected puppies try to walk, between one and two weeks of age. Sometimes, dogs with spina bifida never develop observable symptoms.
Symptoms of Spina Bifida
As mentioned above, some dogs born with spina bifida never show signs of their condition. Owners of dogs that do develop clinical signs may notice one or more of the following signs:
Rear limb paresis (weakness)
Slight to moderate incomplete paralysis of one or both hind legs
Decreased muscle tone (hind end)
Muscle atrophy (hind end)
Ataxia (lack of coordination)
Loss of sensation in the perineal area (the region between the tail and the genitalia)
Decreased anal sphincter tone
Decreased ability to use the tail
In rare cases, there may be a draining mass on the dog's back, towards its tail. Other possible signs are dimpling of the skin and/or abnormal direction of hair growth over the affected area of the animal's spine.
Dogs at Increased Risk
Spina bifida can occur in any dog of any breed or mixed breed and of either sex. However, it is most commonly seen in English Bulldogs (and in Manx cats), which is why a hereditary component to this condition is suspected.
If the spinal cord is unaffected by the defective bone fusion that is called spina bifida, the dog probably will never have symptoms of neurological abnormalities, and the condition actually may never be diagnosed. However, when the spinal cord pushes out through the gap in the abnormal vertebrae, the dog's rear-end ambulation and control of its urinary and rectal function typically are adversely affected.
How Spina Bifida is Diagnosed
A veterinarian should be consulted when a young puppy is not able to walk normally as compared with the abilities of its littermates. The veterinarian will take a history of the puppy's environment and development and will perform thorough physical and neurological examinations. She may or may not be able to localize which areas of the spine are affected based upon the results of those examinations. Additionally, a miminum data base of blood work (a complete blood count and serum biochemistry profile) and a urinalysis are almost always advised to assess the puppy's overall health. This is especially important before heavy sedation or general anesthesia is administered to facilitate a more in-depth neurological examination. An electrocardiogram (ECG) to evaluate heart health, and a thyroid panel to evaluate thyroid gland function, may also be recommended.
Spina bifida normally can be definitively diagnosed with simple radiographs (X-rays). Often, it is discovered incidentally when thoracic (chest), abdominal or hip X-rays are taken for some unrelated reason. Radiographs usually will reveal the anatomical defect in the upper parts of affected vertebrae. Computed tomography (CT scan) and magnetic resonance imaging (MRI) are available in some specialty clinics and at veterinary teaching hospitals; these can be helpful to pinpoint the precise location and the extent of bony and soft tissue abnormalities in dogs with spina bifida. A number of other advanced laboratory and electrodiagnostic tests, such as myelography and cerebrospinal fluid analysis, are available if the veterinarian thinks that they may be helpful in a given case.
It is important for owners to remember that spina bifida may or may not cause any discomfort or noticeable signs in affected animals. If the spinal cord does not protrude from the opening in the unfused vertebrae, the disorder may never be diagnosed and may never need any sort of treatment or medical management.
The management of spine and spinal cord disorders depends upon the nature and severity of the particular abnormality. Treatment is rarely attempted for dogs with spina bifida, mainly because there is no reliable way to "treat" - or fuse - the defect in the abnormal vertebral bones. If a dog has clinical symptoms as a result of a spinal malformation, it means that the spinal cord has already been damaged. At that point, treatment is almost never available or effective.
There is no current treatment for spina bifida in domestic dogs. Attempts to correct the vertebral defects surgically have not been successful, and management with drugs, supplements or dietary modification have no meaningful impact on the condition. Puppies with spina bifida are born with one or more vertebrae that did not develop normally, leaving a gap at the uppermost side of the bone that exposes the spinal cord. The abnormal opening makes the spinal cord vulnerable to trauma and provides a pathway for it to "pop" or squeeze out of its normally protected canal. When this happens, it usually leads to significant neurological damage, because the edges of the gaps in the vertebral bones are rarely smooth and because the spinal cord is extremely fragile. Once the spinal cord is damaged, the adverse consequences are almost always irreversible. Euthanasia is often the most humane alternative for puppies that are severely affected by spina bifida.
However, if the spinal cord of an affected dog does not bulge out through the gap in the upper side of the vertebrae, and if the spinal cord and associated nerves otherwise remain undamaged, the dog may never have noticeable symptoms associated with its condition. In those cases, the animal probably will live a full, happy and pain-free life – at least, without complications of spina bifida - even without any medical treatment for the disorder.
The prognosis and life-expectancy for dogs born with this anatomical spine defect is quite variable. If a dog has significant spinal cord damage caused by the congenital failure of one or more of its vertebrae to fuse, and if it shows severe signs of neurological deficits, its outlook is guarded to grim. These dogs – usually young puppies at the time of diagnosis – often are in a great deal of pain and discomfort. Their inability to walk normally, combined with both fecal and urinary incontinence, probably will prevent them from living an acceptably long or good quality of life. Many caring owners opt for euthanasia when their puppies are so disabled from the disorder. On the other hand, the prognosis for dogs that have no observable symptoms of spina bifida is quite good. They probably should be restricted from engaging in vigorous athletic activities, be well-trained and be encouraged to be calm, in order to enhance their chances of avoiding future spinal cord damage if at all possible.