Cervical disorders of small breed dogs (Proceedings)

Disease processes of the cervical spinal cord and vertebral column and the pain and paresis produced by these disorders are a common cause of presentation to the veterinarian. Some causes of cervical pain are more common or unique to small breeds. Other disorders affect both large and small breed dogs but the clinical course, treatment and prognosis may vary between dogs of different sizes. Fortunately, by recognizing the clinical signs of cervical disease and developing a list of differential diagnoses, a diagnostic and treatment plan can often be formed to help relieve a patient of pain and regain the ability to walk.

Clinical signs of cervical disease

Clinical signs of cervical disease are often dramatic, resulting in severe pain and tetraparesis, but at other times a patient's symptoms can be frustratingly subtle. The first step in identifying a cervical spinal cord or vertebral column disorder is recognizing and localizing the source of the problem. Pet owners usually provide the first clue with their descriptions of their pet's behavior at home. Classic symptoms include a posture in which the patient's head is held low, either extended or retracted toward the shoulders. Often these patients will refuse to look up from the ground, have exaggerated eye movements in an attempt to examine their environment without moving the neck and have cervical musculature fasciculations or spasms. Other dramatic signs of cervical disease include tetraparesis from severe compression or intraparenchymal damage to the spinal cord. Unfortunately, cervical disorders do not always produce such easily recognized signs. Often a pet owner will only notice that their pet cries out in pain intermittently. Sometimes additional questioning about when the pain occurs can be helpful. Important observations from the owner that should raise suspicion of cervical disease include refusing to jump, difficulty flexing the neck to eat and drink from the ground, eating and drinking while laying down, refusing or hesitancy to shake the head and pain when giving medications or treats (because the neck is often extended during these activities). Compression of a cervical nerve root (root signature sign) often results in a posture in which the patient prefers to keep a thoracic limb flexed and held off the ground. Although most pet owners do not recognize this as a possible symptom of neck pain the presence of a root signature sign can be helpful in localizing the source of a patient's discomfort. Root signature pain, however, is less common in large dogs than small breeds. Still other patients have even more subtle signs. Although not specific to cervical disorders, symptoms such as decreased activity and inappetence are often the first and only signs present.

Neurologic examination

Neurologic examination in patients with suspected cervical disease should include all of the areas covered in the complete neurologic examination. These include observation of gait and mentation, assessment of postural reactions, segmental spinal cord reflex evaluation, sensory assessment, cranial nerve examination and palpation of the vertebral column, limb musculature and skull. Details on the neurologic examination and localization of neurologic symptoms can be found elsewhere in these proceedings.

Diagnostic procedures

Once a lesion is localized to the cervical vertebral column a diagnostic plan should be developed to try to ascertain the nature and extent of the disorder. Hematologic, biochemical and urinalysis data are often obtained initially and occasionally provide information that may be specific to a particular disorder. In particular, neoplastic and infectious/inflammatory disorders may produce significant changes on preliminary diagnostic tests.

Survey radiographs are often performed early in the course of diagnostic testing in patients with neck pain. For optimal results, general anesthesia or heavy sedation is recommended when obtaining all vertebral radiographs. Proper positioning is also critical to obtaining the most clinically useful radiographs. Radiographs should always be obtained in two perpendicular planes. In lateral images a properly positioned radiograph has the transverse processes of the vertebrae superimposed over one another. This is best evaluated by observing opposition of the large transverse processes of C1 and C6. In a well positioned ventrodorsal radiograph the dorsal spinous process of the cervical and thoracic vertebrae appear like the keel of a boat centered on the body of the vertebrae. Endotracheal tubes should also be removed when taking a ventrodorsal image. Well positioned and exposed survey radiographs of the cervical vertebral column in anesthetized patients will often reveal evidence of vertebral neoplasia, osteomyelitis, diskospondylitis, congenital vertebral anomalies, fractures/luxations and intervertebral disc extrusion.

Advanced spinal imaging such as myelography, computed tomography (CT) and magnetic resonance imaging (MRI) is often necessary to find the cause of structural disorders. Computed tomography and MRI are especially useful for imaging intradural lesions such as syringomyelia and subarachnoid cysts and obtaining additional information when necessary following a myelogram. Use of CT and MRI is also gaining acceptance as the diagnostic imaging techniques of choice for many disorders, such as intervertebral disc extrusion and caudal cervical spondylomyelopathy, in which traditional myelography was once considered the standard.

Cerebrospinal fluid can be collected from the cerebellomedullary cistern and often provides valuable diagnostic information on patients with cervical disease, especially those with meningitis and neoplasia. A routine spinal fluid analysis consists of evaluation of spinal fluid protein, red and white blood cell counts and cytologic evaluation of the spinal fluid. Additional testing, such as bacterial and fungal culture and serologic testing, is also performed on some patients when indicated. Administration of corticosteroids prior to collection and analysis of cerebrospinal may change or diminish the inflammatory response and if possible should be avoided.

Intervertebral disc extrusion

One of the most common causes of cervical pain in veterinary patients is caused by extrusion of intervertebral disc material into the spinal canal. Chondroid degeneration of the intervertebral disc resulting in type I (acute) extrusion of the nucleus pulposus or a more chronic type II protrusion of the annulus fibrosus may both occur in small breed dogs. Chondrodystrophic breeds such as the Dachshund, Shih tzu, Beagle, Pekinese, and Lhaso apso as well as other small breeds such as Poodles, Pomeranians, Yorkshire Terriers, Chihuahuas, Bichon Frise and Cocker Spaniels have a high frequency of intervertebral disc extrusion. Symptoms range from cervical pain to non-ambulatory tetraplegia, but paresis is not as common in cervical intervertebral disc disease compared to thoracolumbar disc extrusion. In the most severely affected patients cervical pain may be minimal or absent. Cervical intervertebral disc extrusions tend to occur later in life than intervertebral disc extrusions in the thoracolumbar vertebral column. Intervertebral disc extrusion/protrusion at any level is a very unlikely differential diagnosis for patients less than two years of age.

Diagnosis of cervical disc extrusion may be obtained by survey radiographs if calcified disc material can be seen in the spinal canal but an intervertebral disc extrusion can not be ruled out by a normal radiograph. CT myelography or MRI is recommended to confirm the exact location of extruded disc material prior to surgical intervention. This is especially important in the cervical vertebral column since multiple surgical approaches are available in this area of the spine. In small breed dogs, disc extrusions are most common in the cranial to mid cervical vertebral column, but also occur in the lower cervical vertebral column. Small breed dogs have a higher tendency to have multiple disc extrusions/protrusions than patients of large breeds.

Both conservative and surgical treatments are available for patients with cervical intervertebral disc extrusion. Conservative treatment, consisting of strict crate confinement and anti-inflammatory agents, may be attempted the first time a patient experiences mild to moderate pain. Corticosteroids generally provide better anti-inflammatory effects and analgesia than non-steroidal anti-inflammatory drugs (NSAIDs) for cervical disc extrusion, but NSAIDs may provide adequate analgesia in many patients with mild to moderate pain. Mixing corticosteroids and NSAIDs is contraindicated as the chance of gastrointestinal side effects is greatly increased without significantly changing the amount of analgesia provided. Use of analgesics and anti-inflammatory drugs without exercise restriction is also contraindicated and may result in significant worsening of clinical signs. For patients with severe cervical pain, any degree of paresis, or patients with repeat or chronic pain, decompressive surgery is usually necessary to provide long term pain relief. When the disc extrusion is centrally located within the spinal canal, decompression can usually be obtained with a ventral slot decompression. When disc material is located lateral to the spinal cord or within the intervertebral foramen, a dorsal laminectomy or hemilaminectomy is necessary to decompress the spinal cord. The prognosis for recovery for most patients with cervical intervertebral disc extrusions is very good following surgical decompression.

Syringomyelia/hydromyelia

Syringomyelia refers to a fluid filled cavity within the parenchyma of the spinal cord while hydromyelia refers to dilation and accumulation of fluid within the central canal of the spinal cord. Usually a distinction between syringomyelia and hydromyelia requires histologic examination, and for clinical purposes a distinction is not necessary. Therefore, the term syringo/hydromyelia, or just syringomyelia is often used to describe this condition. Syringo/hydromyelia occurs at all levels of the spinal cord but is most common and severe in the cervical spinal cord. Many mechanisms of pathogenesis have been proposed for syringo/hydromyelia and all involve abnormal pressure relationships between the intracranial and intraspinal cerebrospinal fluid spaces. Syringo/hydromyelia may occur alone but more commonly occurs in association with hydrocephalus in young, toy breeds of dogs. Cavalier King Charles Spaniels are especially susceptible to syringo/hydromyelia formation as part of the caudal occipital (Chiari) malformation that is common in this breed. Clinical signs include intermittent cervical pain, progressive tetra or posterior paresis, scoliosis, ataxia and scratching at the shoulders. These clinical signs often wax and wane but symptoms tend to be slowly progressive over time. Diagnosis of syringo/hydromyelia usually requires imaging of the spinal cord with either CT or MRI, as conventional myelography rarely demonstrates the intraparenchymal cavitation. In patients with significant hydrocephalus ventriculoperitoneal shunting is often performed. When this method of treatment is chosen specific treatment of the syringo/hydromyelia may not be needed. In Cavalier King Charles Spaniels with Chiari malformation decompression of the foramen magnum and caudal fossa may result in improvement in clinical symptoms. In other patients in whom surgery has not been performed, long term success has been achieved by reducing cerebrospinal fluid production with corticosteroids and diuretics.

Congenital vertebral malformation

Congenital vertebral malformations occur less commonly in the cervical vertebral column than in other areas of the spine and in most instances are clinically insignificant. Occasionally, however, cervical disease may occur as a result of instability at the site of the congenital malformation or as a result of abnormal stresses applied to surrounding vertebrae. Surgical stabilization and decompression of the spinal cord may be necessary in some patients.

Meningitis/meningomyelitis

Meningitis (inflammation of the meninges) and meningomyelitis (inflammation of the meninges and underlying spinal cord parenchyma) are not single disease entities by themselves but rather terms used to describe inflammation and/or infection of the meninges and spinal cord from bacterial, viral, fungal, protozoal, rickettsial and immune-mediated causes. The pathogenesis of meningitis and meningomyelitis varies with the etiologic agent involved. Clinical signs of meningitis include systemic illness (inappetence, fever, lethargy), cervical and often thoracolumbar pain, neck guarding, and a rigid stance and gait. Patients with meningomyelitis may have these symptoms as well as paresis, ataxia, and reflex changes that may be multi focal in nature. Low grade, chronic causes of meningitis may cause mild symptoms that are only present intermittently. Meningitis/meningomyelitis should be considered high on the list of differential diagnoses in patients with diffuse vertebral pain with or without fever. Demonstration of the meningeal inflammation requires collection and analysis of cerebrospinal fluid. Fluid is collected from either the cerebellomedullary cistern or lumbar cistern, and routine evaluation should include red and white blood cell counts, protein quantification and cytologic examination. It is important to understand that CSF analysis is a sensitive test that will usually demonstrate even mild inflammation, but the inflammatory changes present in the spinal fluid are rarely specific enough to provide a definitive diagnosis. Often, however, certain etiologies can be ruled out by the type of inflammatory response present. Once inflammation within the spinal fluid has been identified additional diagnostic testing, such as serologic testing for various infectious agents and spinal fluid culture, may be performed to look for specific etiologic agents. Unfortunately, a definitive diagnosis is not always possible in patients with meningitis/meningomyelitis. Despite this, many patients can be treated with supportive care and anti-inflammatory drugs, antibiotics/antiprotozoal agents, antifungal and antiviral medications.

Cervical vertebral fractures and luxations

Fractures and luxations of the cervical vertebrae occur less frequently than in other portions of the spine, and although clinical signs can be life threatening (respiratory paralysis) many patients have injuries that can be successfully managed. Clinical signs are variable but may include pain only, tetraparesis, tetraplegia and upper or lower motor neuron symptoms in the thoracic limbs depending on the location of the fracture. Physical examination of patients with suspected cervical fractures/luxations should be done cautiously and cervical manipulation should not be performed until the extent of the injury is known. Care with diagnostic testing is also important. Suspicion of a cervical fracture/luxation is one indication in which survey radiographs taken prior to anesthesia may be indicated, however, the limitations of survey spinal radiographs taken in awake patients still apply. The misdiagnosis of C1 and C2 fractures and luxation is common from over interpretation of poorly positioned cervical survey radiographs. If a patient is anesthetized for survey radiographs care must be taken to keep the cervical vertebral column in a neutral position and to avoid flexion and extension during manipulation. Myelography is seldom necessary in patients with cervical fractures, although CT may be useful for surgical planning if surgical correction is to be performed. If a patient's neurologic symptoms are stable and pain can be controlled, many patients with cervical fractures can be managed with conservative treatment consisting of strict crate confinement and cervical splinting or casting. Various surgical techniques can also be performed but are generally reserved for patients with markedly displaced fractures/luxations, deteriorating neurologic status or uncontrollable pain.

Atlantoaxial subluxation

Atlantoaxial subluxation occurs predominantly in young, toy breed dogs and occurs due to agenesis, hypoplasia or malformation of the dens and lack of ligamentous support from the transverse ligament of the atlas and the dorsal atlantoaxial ligament. Clinical signs may be acute, slowly progressive or intermittent and are often associated with mild trauma. Signs range from cervical hyperesthesia to tetraplegia with respiratory compromise. Diagnosis of atlantoaxial subluxation is usually possible with lateral survey radiographs. Extreme care should be taken not to flex the cervical vertebral column when obtaining radiographs. Abnormalities of the dens are best seen on ventrodorsal or oblique lateral views. For patients with only mild pain cervical splinting and strict crate confinement may resolve the symptoms present, but pet owners must be warned that relapses are common. More definitive treatment often requires surgical stabilization of the atlas and axis, and can be achieved with vertebral body cross pinning, lag screw fixation and various wiring techniques. Prognosis for patients with atlantoaxial subluxation is variable and depends a great deal on the pre-surgical neurologic status.

Neoplasia

Neoplasia involving the cervical spinal cord or vertebral column is less common in small breeds but should remain on the list of differential diagnoses. Additional information on cervical neoplasia is covered in the discussion of large breed cervical disorders.

Fibrocartilagenous embolus (FCE)

FCE is less common in small breeds than larger breed dogs but in Miniature Schnauzers, Miniature Pinchers and Shelties ischemic myelopathy from fibrocartilagenous embolus (FCE) is more common. Additional information on FCE is found in the discussion of large breed cervical disorders.