Breed-specific spinal cord disease
These are degenerative CNS diseases that are often inherited. They cause progressive signs and usually involve many areas of the CNS. The most common neurodegenerative disease specific to the spinal cord is degenerative myelopathy of German Shepherd Dogs and Pembroke Welsh Corgis (with sporadic reports in other breeds). As the predominant signs of this disease are paraparesis and ataxia, it will be discussed in site. However, some neurodegenerative diseases initially cause tetraparesis and ataxia. A list of such diseases can be found in Inherited diseases that can cause UMN signs.
Inherited diseases that can cause UMN signs. Many of these diseases also affect other areas of the CNS and therefore cause other (e.g. cerebellar) signs.
|German Shepherd Dog, Pembroke Corgi, others||Degenerative myelopathy|
|Dalmatian, Labrador Retriever||Leucodystrophy|
|Afghan Hound, Kooiker Hound||Myelopathy|
|Fox Hound, Harrier Hound, Beagle||Hound ataxia|
|West Highland White Terrier, Cairn Terrier||Globoid cell leucodystrophy|
Cervical stenotic myelopathy (Wobbler syndrome)
Cervical stenotic myelopathy (CSM) describes a syndrome of compression of the cervical spinal cord as a result of degenerative changes in the cervical spine. There are many names for this syndrome, including Wobbler syndrome, caudal cervical spondylomyelopathy, cervical malformation / malarticulation and disc-associated Wobbler’s disease.
Clinical signs: Classically this is thought of as a disease of large dog breeds (e.g. Dobermann Pinscher, Dalmatian) and giant breeds (e.g. Great Dane, English Mastiff) but identical changes occur in toy and small breeds such as Chihuahua and Yorkshire Terrier.
Clinical signs include progressive ataxia, tetra-paresis and, sometimes, neck pain. Signs in the pelvic limbs are more severe than the thoracic limbs. Dogs with caudal cervical compression frequently have a short stilted thoracic limb gait with a dysmetric, disconnected pelvic limb gait. Nerve-root entrapment can cause thoracic limb lameness and muscle atrophy; in particular, compression of the suprascapular nerve can produce marked atrophy of the supra- and infra-spinatous muscles, making the scapula spine easily palpable. Although typically this is a chronic progressive disease, acute onset of severe signs can occur.
Pathogenesis: Progressive spinal cord compression results from degenerative changes in the vertebral column (). The changes () include any of the following:
- Hypertrophy and protrusion of the annulus fibrosus, often associated with ‘tipping’ of vertebrae
- Hypertrophy of the ligamentum flavum and dorsal longitudinal ligament
- Hypertrophy of synovial membrane and formation of synovial cysts at the articular facets
- Stenosis of the vertebral canal
- Degenerative joint disease of the articular facets.
The aetiology of these changes is most likely multifactorial. Genetic factors probably play a role, as the disease is seen in specific breeds of dog, but no pattern of inheritance has been established in commonly affected breeds (). Over-nutrition and excess calcium supplementation in the first year of life have been implicated in Great Danes () but correction of these feeding patterns has not prevented occurrence of the disease in this breed. It has also been postulated that conformation of the head and neck influences the development of lesions; however, a study on Dobermann Pinschers failed to find a correlation between various body dimensions and radiographic or neurological signs (). It is believed by many that the degenerative changes seen in this syndrome ultimately result from instability in the cervical spine.
In general, giant breeds present within the first 3 years of life with degenerative changes of the articular facets and their associated synovium, synovial cysts and stenosis of the vertebral canal affecting C3-C6. Large breeds are more likely to present with what has been termed disc-associated Wobbler’s disease or caudal cervical spondylomyelopathy. They develop signs in middle age or older as a result of hypertrophy and protrusion of the annulus, and ligamentous hypertrophy of the dorsal longitudinal ligament and the ligamentum flavum, affecting the caudal cervical vertebrae. The changes in large breeds can be described as static (spinal cord compression not altered by flexion, extension ortraction) or dynamic (compression altered by flexion, extension ortraction). In both large and giant breeds, compressive lesions may be present at more than one site.
Diagnosis: Survey radiographs of the cervical spine may show degenerative changes typical of this syndrome () but cannot be used to identify sites of spinal cord compression. Stressed views should not be taken as compression of the spinal cord can be exacerbated. Myelography combined with computerized tomography (CT) can be used to diagnose CSM and to plan surgery (). Linear traction views of the myelogram are used to determine whether compression can be addressed by distraction and fusion of vertebrae (i.e. a dynamic lesion) (). Magnetic resonance imaging (MRI) is being increasingly used to identify sites of compression, particularly in giant breeds ().
Treatment and prognosis:
Conservative management: It is recommended that dogs with neurological deficits are treated surgically, as this is a chronic progressive disease. However, many owners cannot afford or do not wish to have surgery performed and conservative therapy can be considered in such cases and in dogs with mild deficits. Conservative management includes treatment of pain with anti-inflammatory drugs and muscle relaxants, and restriction of unmonitored activity combined with controlled exercise and physical therapy (). Acupuncture can be useful for controlling chronic pain in some dogs. Dogs managed in this way should be monitored weekly to biweekly to allow early recognition of deterioration and recommendation for surgical intervention. Dogs that are non-ambulatory may respond to conservative management but surgery is strongly recommended.
Surgical management: The aims of surgery are to decompress and / or stabilize the cervical spine. Surgical strategies include the ventral slot (to remove disc material from the canal), distraction / stabilization techniques (to treat lesions responsive to traction) and dorsal laminectomy (to remove dorsal compression or address multiple disc protrusions). Surgical decisions are based on the type and number of lesions present and a full discussion of the different surgeries can be found in McKee and Sharp (). Postoperative rehabilitation of patients is critical to their recovery and owners need to be fully informed about the implications of rehabilitating a non-ambulatory large or giant breed dog (). Rehabilitation includes passive range-of-motion exercises and massage in the recumbent dog, and hydrotherapy and controlled exercise if the animal is ambulatory. Due to the chronic nature of the disease, recovery of these dogs can be prolonged (6-12 weeks or more).
When dogs with disc-associated Wobbler’s disease are considered, success rates with surgery are about 80% in the short term (< 1 year) (). The presence of multiple lesions and severe neurological deficits (i.e. non-ambulatory) worsens the prognosis. The prognosis in the long term is not as good, with a recurrence of signs developing in about 20% of dogs. This is usually a result of new lesions developing at sites adjacent to the previous surgery (the domino effect) () Early surgical fusion of suspicious sites adjacent to the main lesion may help to reduce this problem in the future.
Cervical disc disease
Clinical signs: Onset of signs can occur from 18 months of age, with a peak incidence between 3 and 7 years of age. It is very unusual for a disc herniation to occur in dogs <2 years of age, as the predisposing degenerative changes have not often occurred. The most common presenting sign is severe neck pain, as there is enough space within the cervical vertebral canal for herniation of disc material without compression of the spinal cord (). The dog may adopt a stance with the head held down, neck rigid and back arched as the weight is shifted to the pelvic limbs (). Entrapment of nerve roots can cause a nerve-root signature (holding up a thoracic limb and lameness). The neck pain can be so severe that the dog avoids moving its head, and spasm and rigidity of the cervical musculature are easily palpable. Neurological deficits are less common but can occur when the spinal cord is sufficiently compressed and range from tetraparesis with ataxia and conscious proprioceptive and postural-reaction deficits to tetraplegia.
Pathogenesis: Cervical disc disease is a common problem in chondrodystrophoid breeds of dog such as Dachshund, Shih Tzu and Pekingese. It also occurs frequently in Beagles and Cocker Spaniels and can occur sporadically in almost any breed. Thoracolumbar disc herniations are well recognized in cats (); cervical disc herniations have been reported () but are extremely rare in this species. The intervertebral disc is composed of an outer fibrous portion (the annulus fibrosus) and a gelatinous centre (the nucleus pulposus). With normal ageing the nucleus is slowly replaced by fibrocartilage (fibroid metamorphosis), but in chondrodystrophoid breeds the nucleus ages prematurely and the nucleus matrix degenerates and mineralizes (chondroid metamorphosis) (). As a result of these degenerative changes, affected dogs are prone to extrusion of the mineralized nucleus pulposus into the spinal canal (Hansen type I disc herniations), causing spinal cord concussion and compression (). The C2 / 3 disc is most commonly affected, with incidence decreasing further caudally in the cervical spine ().
Diagnosis: Survey spinal radiographs should betaken to identify degenerative changes typical of a disc hemiation and to rule out other causes of the signs. Changes indicative of a disc herniation include narrowing of the intervertebral disc space, narrowing of the intervertebral foramen and the presence of mineralized material within the vertebral canal and disc space (). A definitive diagnosis with adequate accuracy for surgery to be undertaken cannot be reached with survey radiographs alone and so either CT, myelography or MRI is used to identify the site of spinal cord compression (). Cerebrospinal fluid (CSF) analysis is performed concurrently to rule out an inflammatory disorder.
Treatment and prognosis:
Conservative management: Dogs can be managed conservatively with strict cage rest for 4 weeks combined with pain relief using anti-inflammatory drugs, opioids or muscle relaxants. Judicious use of anti-inflammatory doses of corticosteroids combined with appropriate cage confinement can be attempted if the pain is not responsive to non-steroidal anti-inflammatory drugs (NSAIDs). Muscle spasm can also be responsive to gentle massage and hot packing of the neck or to oral diazepam administration (0.5 mg / kg q8-12h). Administration of an H2 receptor antagonist such as famotidine or ranitidine may help to prevent the development of gastric ulceration. The aim of cage rest is to allowdefects in the annulus fibrosus to heal, and resolution of pain does not mean that confinement should be discontinued. If this approach is successful, gradual reintroduction to controlled exercise can be attempted and in the long term the owners should be cautioned to prevent their pet from activities that involve jumping. Dogs should be monitored weekly: if the pain is unresponsive to conservative therapy or recurs, or if neurological deficits develop, surgery should be recommended.
Surgical management: Indications for surgery include unremitting or severe pain, recurrent pain, or neurological deficits. Once the site of disc herniation has been confirmed, a ventral slot is performed to remove the herniated disc material (). Adjacent discs are fenestrated to prevent recurrence of the problem. Post-operativeiy, dogs are provided with pain relief and confined for 4 weeks (2 weeks of strict confinement and then, if doing well, 2 weeks of increasing controlled exercise). Dogs are then gradually re-introduced to normal activity. If the dog has neurological deficits, postoperative care includes passive range-of-motion exercises, massage, hydrotherapy and controlled exercise ().
The prognosis for dogs treated conservatively is unknown. The prognosis for dogs treated surgically is excellent, unless neurological deficits are severe.
Clinical signs: Neurological deficits include spinal hyperaesthesia and signs of a chronic and progressive myelopathy reflecting the site of the lesion.
Pathogenesis: Large cysts can develop from the synovial membranes around the articular processes, causing dorsolateral compression of the spinal cord. This can occur as a component of cervical stenotic myelopathy (see above) or be an isolated disorder. Affected dogs are typically either young giant breeds with multiple cysts present in the cervical spine, or older large breeds with single cysts in the thoracolumbar spine ().
Diagnosis: Degenerative joint disease of the affected articular processes is usually visible on survey radiographs. Extradural lesions causing dorsolateral spinal cord compression are visible on myelography (with or without CT) and on MR images. There are non-specific changes on cerebrospinal fluid analysis. The precise nature of the lesion is confirmed at surgery.
Treatment and prognosis: The spinal cord can be decompressed by surgical removal of the cysts. This is usually achieved by a dorsal laminectomy in the cervical spine and a hemilaminectomy in the thoracolumbar spine. Prognosis is usually good in uncomplicated cases addressed early.
Calcinosis circumscripta (tumoral calcinosis)
Clinical signs: Affected dogs show progressive tetraor paraparesis, depending on lesion location.
Pathogenesis: This is an unusual disease of young large breed dogs, such as the German Shepherd Dog and Rottweiler. Mineralization of the ligamentous structures of the vertebral column, usually either dorsal to the atlantoaxial junction () or dorsal to the mid thoracic spine causes pain and compression of the spinal cord (Lewis and Kelly, 1990). Both renal disease and trauma are known to cause ectopic mineralization but there is no evidence of either problem in these dogs. Postulated causes include a foreign body reaction to aberrant mesenchymal tissue and an as yet unidentified inherited defect of calcium and phosphate homeostasis ().
Diagnosis: Diagnosis can be made from a survey spinal radiograph. Routine blood work should be done, to rule out renal disease and to check calcium and phosphate levels. Parathyroid hormone levels can be measured. Radiography of the limbs should also be done, to identify other sites of soft tissue mineralization.
Treatment and prognosis: Surgical decompression is recommended and is successful in dogs with single lesions, mild to moderate neurological deficits and no evidence of an underlying cause.