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Cervical Spondylomyelopathy
This disease, also called cervical vertebral malformation-malarticulation and wobbler syndrome, is compression of the spinal cord caused by abnormal development of the cervical vertebrae. Genetic factors and possibly nutrition may be involved.
In dogs, middle-aged Doberman Pinschers and young Great Danes are most commonly affected, but the condition occurs in many large breeds. The specific pathologic changes vary but may include stenosis of the vertebral canal, malformation of the articular facets, disk protrusion, synovial cysts, and vertebral instability. The C5–6 and C6–7 vertebrae and disk spaces are most commonly affected. Clinical signs can be acute or slowly progressive. Mild cases are characterized by subtle ataxia of all limbs, often evident as a long, protracted stride in the pelvic limbs, with short-strided gait in the thoracic limbs. In severe cases there is paresis or paralysis of all limbs. Neck pain is variable.
Differential diagnoses include congenital anomalies, trauma, meningomyelitis, discospondylitis, and neoplasia. Definitive diagnosis is based on spinal imaging with myelography, CT, or MRI. Nonsurgical treatment consists of exercise restriction and anti-inflammatory medication. Surgery is indicated in animals with substantial neurologic deficits and those that do not respond adequately to nonsurgical treatment. The specific technique is based on the changes evident on imaging and include ventral slot with partial diskectomy, dorsal laminectomy, or distraction and fusion of affected vertebrae. Overall, about 75% of patients do well with surgery.
In horses, cervical spondylomyelopathy is the most common noninfectious disease of the spinal cord and occurs in many breeds. Most horses present at <3 yr of age, although any age can be affected. The mid-cervical region is most commonly affected, and there is spinal ataxia and tetraparesis. Diagnosis is based on imaging and excluding other causes. Plain radiographs may show abnormal articular facets and stenosis of the vertebral canal. Myelography is necessary for definitive diagnosis and surgical planning. Nonsurgical treatment involves NSAID and dimethyl sulfoxide to reduce inflammation. In yearlings, diet modification can help. Surgery most commonly involves ventral fusion of the affected vertebrae. About 80% of affected horses improve with surgery. Owner/rider safety is a major concern in horses with ataxia.
Degenerative Lumbosacral Stenosis
Narrowing of the lumbosacral vertebral canal or intervertebral foramina results in compression of the cauda equina or nerve roots. It is most common in large breeds of dogs, especially German Shepherds, and is rare in cats. It results from degeneration and protrusion of the L7–S1 disk, hypertrophy of the ligamentum flavum, or rarely subluxation of the lumbosacral joint. The cause is unknown, although German Shepherds with congenital transitional vertebrae are at increased risk. Clinical signs typically begin at 3–7 yr of age and may include difficulty using the pelvic limbs, pelvic limb lameness, tail weakness, and incontinence. Pain on palpation or extension of the lumbosacral joint is the most consistent finding. There may be proprioceptive deficits, muscle atrophy, or a weak flexor reflex in the pelvic limbs. Plain radiographs may show degenerative changes, but definitive diagnosis requires MRI, CT, or epidurography. Dogs in which mild pain is the only sign may improve with 4–6 wk of rest. Surgery is indicated when pain is refractory to medical therapy or there are neurologic deficits. The most common technique is dorsal laminectomy with partial diskectomy, but foramenotomy or stabilization is indicated in certain cases. Prognosis for recovery is good, although urinary incontinence may not resolve.
Degenerative Myelopathy of Dogs
This disease, also called chronic degenerative radiculomyelopathy, is a slowly progressive, noninflammatory degeneration of the axons and myelin primarily affecting the white matter of the spinal cord. It is most common in German Shepherds, Pembroke Welsh Corgis, Boxers, Rhodesian Ridgebacks, and Chesapeake Bay Retrievers, but is occasionally recognized in other breeds. The cause is a mutation in the superoxide dismutase-1 gene, inherited in an autosomal recessive pattern with incomplete penetrance. It is similar to familial amyotrophic lateral sclerosis in human patients. Pathologically, there is noninflammatory degeneration of axons in the white matter of the spinal cord, which is most severe in the thoracic region.
Affected dogs are usually >8 yr old and develop an insidious onset of nonpainful ataxia and weakness of the pelvic limbs. Spinal reflexes are usually normal or exaggerated, but in advanced cases there is flaccid tetraparesis and hyporeflexia reflecting lower motor neuron involvement. Early cases may be confused with orthopedic disorders; however, proprioceptive deficits are an early feature of degenerative myelopathy and are not seen in orthopedic disease.
Myelography or MRI and CSF analysis are essential to rule out compressive and inflammatory diseases. Genetic testing is available and aids diagnosis as well as detection of carriers, which should facilitate breeding strategies to decrease the incidence of the disease. There is no specific treatment. Most dogs are euthanized due to disability within 1–3 yr of diagnosis.
Equine Degenerative Encephalomyelopathy
This progressive neurologic disorder of horses and zebras is characterized by diffuse degeneration of axons, myelin, and neurons in the spinal cord and, to a lesser degree, the brain stem. It has been reported in many equine breeds in North America, Australia, and England. The etiology is incompletely understood, but a vitamin E deficiency and genetic factors are suspected. Clinical signs usually become apparent during the first year of life and consist of ataxia and weakness in all 4 limbs, although the hindlimbs may be more severely affected. Clinical signs may stabilize or slowly progress. Myelography and CSF analysis are normal. Vitamin E supplementation is preventive in some cases, and affected horses may improve with supplementation.
Intervertebral Disk Disease
Degeneration and protrusion of the intervertebral disk results in compression of the spinal cord, spinal nerve, and/or nerve root. It is a common cause of spinal cord disease in dogs. Clinical signs due to disk disease are rare in cats and horses. Chondrodystrophoid breeds of dogs (eg, Dachshund, Beagle, Shih Tzu, Lhasa Apso, and Pekingese) are most commonly affected. In these breeds, there is chondroid degeneration of the disks within the first few months of life. Disk extrusion can occur as early as 1–2 yr of age, and clinical signs are often acute and severe. In contrast, fibroid disk degeneration typically occurs in large breeds of dogs >5 yr old and causes slowly progressive clinical signs.
The most common sites of disk extrusion are the cervical and thoracolumbar regions. The predominant sign of cervical disk extrusion is neck pain, manifested as cervical rigidity and muscle spasms. There may be thoracic limb lameness or neurologic deficits, ranging from mild tetraparesis to tetraplegia. In thoracolumbar disk extrusion, there may be back pain, evident as kyphosis and reluctance to move. Neurologic deficits are usually more severe than those seen in cervical disk disease and range from pelvic limb ataxia to paraplegia and incontinence. In paraplegic animals, the most important prognostic finding is whether or not there is deep pain perception caudal to the lesion. This is assessed by pinching the toe or tail and observing whether or not there is a behavioral response, such as a bark or turn of the head. Reflex flexion of the limb must not be mistaken for a behavioral response.
Definitive diagnosis of disk extrusion is based on imaging studies such as radiography, myelography, MRI, or CT. Dogs with pain and minimal to moderate neurologic deficits often recover with 2–3 wk of cage rest. A short course of prednisone (0.5 mg/kg/day for 3 days) is often helpful in relieving pain. The use of anti-inflammatory or analgesic medication without concurrent cage rest is contraindicated because an increase in the dog's activity may lead to further disk extrusion and worsening of spinal cord compression. Clinical signs recur after conservative therapy in 30–40% of cases.
In animals with severe neurologic deficits, methylprednisolone sodium succinate may improve recovery of severe spinal cord injuries if given within 8 hr of injury, although it is unclear whether the benefits outweigh risks (see Diseases of the Peripheral Nerve and Neuromuscular Junction: Trauma of the Peripheral Nerve and Neuromuscular Junction). Medical therapy, however, is not a substitute for surgery, which should be performed promptly to decompress the spinal cord in animals with substantial neurologic deficits. Other indications for surgery are failure of conservative therapy and recurrent episodes. The prognosis is good for dogs with intact deep pain perception that are treated surgically. If surgery is performed within 24 hr of the loss of deep pain perception, the chance of recovery is ~50%. If surgery is delayed for >48 hours after deep pain perception is lost, the prognosis is poor. Progressive myelomalacia develops in 5–10% of dogs with paraplegia and loss of deep pain perception. In this syndrome, affected dogs develop flaccid tetraplegia, the level of anesthesia ascends cranially, and respiratory paralysis develops.
Equine Motor Neuron Disease
This progressive, noninflammatory degeneration of motor neurons in the spinal cord and brain stem of horses is most common in the northeastern USA but has been reported in several areas of North and South America, Europe, and Japan. The etiology is uncertain, but vitamin E deficiency is a strong risk factor. Adult horses of any age and breed can be affected, although Quarter Horses are affected most commonly. Affected horses typically do not have access to pasture grass and are fed grass hay.
Clinical signs consist of generalized symmetric weakness, trembling, and muscle atrophy. Affected horses often stand with their head held low and their feet camped under their body, frequently shifting their weight from one limb to another. Ataxia is not a feature of this disease, in contrast to most spinal cord diseases. Many affected horses have retinal abnormalities, including a distinct reticulated pigment pattern and areas of hyperreflectivity. Electromyography and biopsy of the spinal accessory nerve or the sacrodorsalis caudalis muscle are useful in the diagnosis.
There is no specific treatment, but some horses improve partially after 2–3 mo of illness. Horses that lack access to green forage high in vitamin E for prolonged periods should be supplemented with vitamin E.
Degeneration of Motor Neurons
This inherited or sporadic disease has been seen in Brittany Spaniels, Pointers, German Shepherds, Doberman Pinschers, and Rottweilers; cats; Hereford, Brown Swiss, and red Danish cattle; Yorkshire pigs; and goats.
Metabolic Storage Disorders
Rare, usually inherited, metabolic disorders can affect the CNS, including the spinal cord. (Also see Congenital and Inherited Anomalies of the Nervous System.)
Spondylosis Deformans
This noninflammatory, degenerative disease is characterized by production of osteophytes along the ventral and lateral aspects of the vertebral bodies. In advanced cases, the osteophytes may appear to bridge the intervertebral disk space. It is seen in dogs, cats, and bulls, and the incidence increases with age. The cause is breakdown of the outer fibers of the annulus fibrosis and stretching of the longitudinal ligament. The increased stress at the vertebral attachment of the longitudinal ligament incites osteophyte production. It is usually an incidental radiographic finding. Rare cases cause spinal hyperesthesia, which should be treated with analgesics.
Last full review/revision July 2011 by William B. Thomas, DVM, MS, DACVIM (Neurology)
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