Cervical Spondylomyelopathy

Cervical spondylomyelopathy (CSM), also known as cervical vertebral instability, cervical vertebral malformation-malarticulation, or wobbler syndrome, is a multifactorial disorder of the cervical vertebral column characterized by spinal cord compression due to vertebral malformation, malarticulation, intervertebral disc protrusion, and/or ligamentous hypertrophy. It primarily affects large and giant breed dogs, causing progressive ataxia and paresis. The condition is classified into two main types: Type I (disc-associated) and Type II (osseous-associated). Type I typically occurs in middle-aged large breeds, such as Doberman Pinschers, and involves chronic intervertebral disc protrusion, often at C5-C6 or C6-C7. Type II is more common in young giant breeds, such as Great Danes and Mastiffs, and is characterized by vertebral canal stenosis due to bony proliferation and malformation, often involving multiple sites. Surgical management aims to decompress the spinal cord and stabilize the affected vertebral segments.

The exact etiology of CSM is multifactorial and not fully understood. Genetic predisposition plays a significant role, with certain breeds showing high heritability. Nutritional factors, such as excessive calcium and calorie intake during growth, have been implicated in the development of osseous-associated CSM in giant breeds. Biomechanical factors, including repetitive trauma to the cervical spine from leash pulling or head carriage, may contribute to disc degeneration and ligamentous hypertrophy. Congenital vertebral malformations, such as hemivertebrae or block vertebrae, can predispose to instability. Degenerative changes in the intervertebral discs, leading to protrusion, are common in Type I CSM. Ligamentous hypertrophy, particularly of the ligamentum flavum and dorsal longitudinal ligament, can cause dynamic spinal cord compression. In some cases, synovial cysts or articular facet hypertrophy may contribute to compression. Traumatic events may exacerbate pre-existing lesions but are rarely the sole cause.

CSM predominantly affects large and giant breed dogs. Type I CSM is most commonly seen in Doberman Pinschers, with a mean age of onset around 6 years, but can also occur in other large breeds such as Rottweilers, Bernese Mountain Dogs, and Labrador Retrievers. Type II CSM is typically diagnosed in young giant breeds, including Great Danes, Mastiffs, and Bernese Mountain Dogs, often before 3 years of age. Males are overrepresented in some studies, possibly due to larger size and faster growth rates. The condition is less common in cats, but has been reported in large breed cats. The incidence in Doberman Pinschers is estimated to be around 5-10% in some populations. Working dogs, such as police and military dogs, may be at higher risk due to physical demands. Breed-specific anatomical variations, such as a narrower vertebral canal in Dobermans, contribute to the predisposition.

The pathophysiology of CSM involves progressive spinal cord compression due to a combination of static and dynamic factors. In Type I CSM, chronic intervertebral disc degeneration leads to protrusion of the annulus fibrosus and nucleus pulposus into the vertebral canal, typically at C5-C6 or C6-C7. This causes ventral spinal cord compression. In Type II CSM, vertebral malformation and malarticulation result in stenosis of the vertebral canal, often due to proliferation of the dorsal lamina, articular facets, and pedicles. Ligamentous hypertrophy, especially of the ligamentum flavum, can cause dorsal compression. Dynamic compression occurs during neck flexion or extension, as the vertebral instability allows abnormal movement that exacerbates the compression. The spinal cord undergoes demyelination, axonal degeneration, and neuronal loss due to chronic compression and ischemia. Vascular compromise, including venous congestion and arterial insufficiency, contributes to neuronal damage. Inflammatory responses, including microglial activation and cytokine release, further exacerbate the injury. The result is progressive neurological deficits, including ataxia, proprioceptive deficits, and paresis.

Intrinsic risk factors include breed predisposition, with Doberman Pinschers and Great Danes being particularly susceptible. Genetic factors are significant, with a heritable component in some breeds. Rapid growth and large body size are risk factors, especially in giant breeds. Nutritional factors, such as overfeeding and excessive calcium intake, can predispose to developmental abnormalities. Age is a factor, with Type I occurring in middle-aged dogs and Type II in young adults. Extrinsic factors include trauma, such as jumping or falling, which can exacerbate underlying instability. Repetitive stress on the cervical spine from leash pulling or head collars may contribute. Prior cervical surgery or injury can also predispose to the condition. Obesity may increase the load on the cervical spine, worsening clinical signs.

Clinical signs of CSM are progressive and vary depending on the severity and location of spinal cord compression. Early signs include mild ataxia, particularly in the pelvic limbs, and a 'wobbly' gait. As the condition progresses, proprioceptive deficits become apparent, with knuckling, crossing of limbs, and a wide-based stance. Thoracic limbs may also be affected, showing spasticity or weakness. Neck pain is variable but can be present, especially with dynamic compression. In severe cases, tetraparesis or tetraplegia may occur. Neurological examination typically reveals upper motor neuron signs in the pelvic limbs, such as increased spinal reflexes and spasticity, while thoracic limbs may show lower motor neuron signs if the lesion is at the C6-T2 intumescence. Postural reactions, such as proprioceptive positioning and hopping, are delayed. Cervical hyperesthesia may be elicited on palpation or manipulation. In Type II CSM, signs may be more acute and severe due to multiple sites of compression.

Differential diagnoses for CSM include: 1) Intervertebral disc disease (IVDD) - acute or chronic disc herniation, often at C2-C3 or C3-C4, causing similar signs; MRI shows disc extrusion. 2) Neoplasia - primary or metastatic tumors of the cervical spine, such as meningioma, lymphoma, or osteosarcoma; imaging shows a mass lesion. 3) Meningomyelitis - infectious or inflammatory disease, such as discospondylitis or steroid-responsive meningitis; CSF analysis and MRI findings. 4) Atlantoaxial instability - congenital or traumatic instability of C1-C2, causing acute or progressive signs; radiography or CT shows subluxation. 5) Fibrocartilaginous embolic myelopathy (FCE) - acute spinal cord infarction, often non-painful; MRI shows intramedullary lesion. 6) Syringomyelia - fluid-filled cavity in the spinal cord, often associated with Chiari-like malformation; MRI shows syrinx. 7) Cervical spinal stenosis - congenital or acquired narrowing of the vertebral canal, often seen in young giant breeds; imaging shows stenosis. 8) Trauma - vertebral fracture or luxation, causing acute signs; radiography or CT shows fracture. 9) Discospondylitis - infection of the intervertebral disc and adjacent vertebrae, causing pain and neurological deficits; radiography shows lysis and sclerosis. 10) Degenerative myelopathy - progressive spinal cord disease, typically in older large breeds, causing pelvic limb ataxia; MRI and CSF analysis rule out other causes.

The diagnostic algorithm for CSM begins with a thorough history and complete neurological examination. If CSM is suspected, survey radiographs of the cervical spine are obtained to evaluate vertebral alignment, disc spaces, and bony abnormalities. However, radiographs are often inconclusive. Myelography, with or without computed tomography (CT), can be used to identify sites of spinal cord compression, but has been largely replaced by magnetic resonance imaging (MRI). MRI is the gold standard for diagnosing CSM, as it provides detailed soft tissue contrast, allowing visualization of disc protrusion, ligamentous hypertrophy, and spinal cord compression. CT is useful for evaluating bony changes, such as vertebral malformation and stenosis. In some cases, cerebrospinal fluid (CSF) analysis is performed to rule out inflammatory or infectious diseases. Electromyography (EMG) may be used to assess nerve root involvement. The diagnostic algorithm should progress from non-invasive to invasive imaging, with MRI being the definitive diagnostic tool.

Laboratory findings in CSM are typically unremarkable. Complete blood count (CBC) and serum biochemistry profile are usually within normal limits. However, they are important to rule out other systemic diseases and to assess anesthetic risk. Coagulation panel (PT/aPTT) is recommended before surgery. Cerebrospinal fluid (CSF) analysis may show mild albuminocytologic dissociation, with elevated protein but normal cell count, due to chronic spinal cord compression. Inflammatory or infectious causes would show pleocytosis and elevated protein. Synovial fluid analysis is not typically performed unless there is concurrent joint disease. In cases with concurrent discospondylitis, blood cultures may be positive. Inflammatory biomarkers, such as C-reactive protein (CRP), may be elevated in inflammatory conditions but are not specific for CSM.

Radiography: Survey radiographs of the cervical spine may show vertebral malformation, malarticulation, narrowed disc spaces, and spondylosis. However, radiographs are not sensitive for detecting spinal cord compression. Myelography, with contrast injected into the subarachnoid space, can show attenuation of the contrast column at the site of compression, but is invasive and has been replaced by MRI. CT: Computed tomography provides excellent bony detail and can show vertebral canal stenosis, articular facet hypertrophy, and vertebral malformation. CT myelography can be used to identify compression sites. MRI: Magnetic resonance imaging is the preferred imaging modality. It provides high-resolution images of the spinal cord, intervertebral discs, and ligaments. Findings include intervertebral disc protrusion, spinal cord compression, and increased signal intensity within the spinal cord on T2-weighted images, indicating edema or myelomalacia. MRI can also identify ligamentous hypertrophy and synovial cysts. Advanced imaging is essential for surgical planning.

Cytology and histopathology are not typically performed for CSM unless there is a suspicion of neoplasia or inflammatory disease. If a mass lesion is identified on imaging, fine-needle aspiration or biopsy may be performed. Histopathology of the spinal cord in chronic CSM shows demyelination, axonal degeneration, and gliosis. In cases of disc-associated CSM, the intervertebral disc shows degenerative changes, including chondroid metaplasia and fibrosis. Ligamentous hypertrophy shows fibrosis and myxoid degeneration. If surgery is performed, tissue samples may be submitted for histopathology to rule out other diseases.

Treatment of CSM can be medical or surgical. Medical management is recommended for mild cases or when surgery is not feasible. It includes strict rest, anti-inflammatory drugs (e.g., prednisone 0.5-1 mg/kg PO q12h, tapering), and muscle relaxants (e.g., methocarbamol 15-20 mg/kg PO q8h). Weight management and physical therapy are important. Surgical treatment is indicated for moderate to severe neurological deficits or when medical management fails. Surgical options include: 1) Ventral slot decompression: This is the most common procedure for Type I CSM, where a rectangular slot is created in the ventral aspect of the vertebral bodies over the affected disc space, and the protruding disc material is removed. This provides direct decompression of the spinal cord. 2) Dorsal laminectomy: This is used for dorsal compression, such as ligamentous hypertrophy or articular facet proliferation. It involves removing the dorsal lamina and any compressive tissue. 3) Vertebral stabilization: This is used for instability, such as in Type II CSM. Techniques include distraction-stabilization with pins and polymethylmethacrylate (PMMA) or plates and screws. The goal is to stabilize the affected segments and prevent dynamic compression. 4) Combined decompression and stabilization: In some cases, both decompression and stabilization are necessary. Postoperative care includes pain management, antibiotics, and physical rehabilitation. The choice of surgical technique depends on the location and type of compression, as well as the surgeon's preference.

The prognosis for CSM varies depending on the severity of neurological deficits, the type of CSM, and the success of surgical decompression. For Type I CSM, the prognosis is generally good, with improvement in 70-90% of dogs after ventral slot decompression. However, recurrence can occur in up to 30% of cases. For Type II CSM, the prognosis is more guarded, especially if multiple sites are affected. Surgical stabilization can improve neurological function in 50-80% of cases, but complications such as implant failure and infection are more common. Negative prognostic indicators include severe neurological deficits, chronicity, and the presence of spinal cord atrophy on MRI. Dogs that are non-ambulatory at the time of surgery have a poorer prognosis. Overall, early diagnosis and surgical intervention improve the outcome.

Postoperative follow-up is crucial for monitoring recovery and detecting complications. Sutures are typically removed 10-14 days after surgery. Neurological examinations should be performed at 2, 4, 8, and 12 weeks postoperatively. Radiographs or CT may be repeated at 4-8 weeks to assess implant placement and bone healing. Activity restriction is recommended for 6-8 weeks, with gradual return to normal activity. Physical therapy, including passive range of motion exercises and controlled walking, should be initiated early. Long-term follow-up every 6-12 months is recommended to monitor for recurrence or progression. Owners should be advised to avoid activities that stress the cervical spine, such as jumping or rough play.

Pearls: 1) Accurate localization of the compression site is essential; MRI is the gold standard. 2) In Type I CSM, ventral slot decompression should be performed at the correct disc space, and the slot should be wide enough to adequately decompress the spinal cord. 3) In Type II CSM, stabilization is often necessary to prevent dynamic compression. 4) Postoperative physical therapy is critical for optimal recovery. 5) Use of a neck brace or collar may help prevent excessive neck movement. Pitfalls: 1) Performing surgery at the wrong site due to inadequate imaging. 2) Incomplete decompression, leading to persistent compression. 3) Damage to the spinal cord during surgery, causing iatrogenic injury. 4) Failure to recognize multiple compression sites. 5) Inadequate stabilization, leading to implant failure or continued instability. 6) Postoperative infection, which can be minimized with strict aseptic technique and appropriate antibiotics.

Perioperative antimicrobial prophylaxis: Cefazolin 22 mg/kg IV at induction and every 90 minutes during surgery. Postoperative antibiotics are not routinely recommended unless infection is suspected. Analgesia: Preoperative opioids such as hydromorphone 0.05-0.1 mg/kg IV or morphine 0.5-1 mg/kg IM. Intraoperative fentanyl CRI at 5-10 mcg/kg/hr. Postoperative analgesia: Fentanyl CRI at 2-5 mcg/kg/hr for 24-48 hours, then transition to oral opioids such as tramadol 2-5 mg/kg PO q8-12h. NSAIDs: Carprofen 2.2 mg/kg PO q12h or meloxicam 0.1 mg/kg PO q24h, starting after surgery if no contraindications. Muscle relaxants: Methocarbamol 15-20 mg/kg PO q8h for 5-7 days. Corticosteroids: Dexamethasone 0.1-0.2 mg/kg IV intraoperatively, then prednisone 0.5 mg/kg PO q12h tapering over 2 weeks. Gastroprotectants: Omeprazole 1 mg/kg PO q12h or famotidine 0.5 mg/kg PO q12h. Chondroprotectants: Polysulfated glycosaminoglycan 4.4 mg/kg IM or SC twice weekly for 4 weeks, or oral glucosamine/chondroitin supplements.

Several studies have evaluated the outcomes of surgical treatment for CSM. A retrospective study by da Costa et al. (2008) reported that 80% of Doberman Pinschers with Type I CSM improved after ventral slot decompression. Another study by De Risio et al. (2002) found that dogs with Type II CSM treated with dorsal laminectomy had a 60% improvement rate. A meta-analysis by Jeffery et al. (2013) concluded that surgical treatment is superior to medical management for moderate to severe CSM. Consensus guidelines from the American College of Veterinary Surgeons (ACVS) recommend MRI for accurate diagnosis and surgical planning. A study by Martin-Vaquero et al. (2015) showed that dogs with spinal cord atrophy on MRI had a poorer prognosis. Overall, the evidence supports surgical decompression and/or stabilization for CSM, with better outcomes in dogs with mild to moderate deficits.