Perspective on Cervical Vertebral
Malformation/Malarticulation (Wobblers Disease)

James Tomlinson United States

A variety of disease conditions affect the cervical spinal cord resulting in neurological deficits and disability for the animal. Establishing a precise diagnosis is required to advise the owner about possible treatment options and prognosis. The early course of many cervical diseases may be similar, making diagnostic testing mandatory to establish a diagnosis.

Caudal cervical spondylomyelopathy (CCSM) is commonly referred to as Wobblers syndrome and cervical vertebral instability.(1) The pathological abnormalities associated with caudal cervical spondylomyelopathy can be roughly divided into two groups based on the age at presentation. Young dogs (Great Danes less than two years of age) typically have vertebral malformation with accompanying secondary soft tissue changes that cause spinal cord compression.(2,3) Middle-aged dogs (Doberman Pinschers four to 10 years of age) have spinal cord compression as a result of hypertrophy of the dorsal annulus fibrosis or Hansen type 2 disk rupture.(1-3) Numerous other breeds of dogs have been diagnosed with CCSM and they typically are large or giant breeds.(2,3)

The first part of the discussion of CCSM will focus on the disease as seen in the middle-aged dog (typically Doberman Pinscher) with the hypertrophy of the dorsal annulus fibrosis or Hansen type II disk disease. Most dogs with CCSM will be presented with a slow progressive onset that gradually worsens with time (65%).(1) Twenty percent of dogs will have a slow progressive onset of the disease with an acute worsening of the clinical signs while 15% will have an acute onset of clinical signs with no previous problems noted.(1) Males have a higher incidence of CCSM than females.(1,4) Age at presentation varies from 1.5 to 12 years of age, with the majority of the dogs falling into the four to eight year old age group.(1,4) Most of the large breeds of dogs can be affected with disease.(1,4)

The presenting condition of an affected dog will range from mild ataxia of the rear legs to nonambulatory tetraparesis, with most dogs having a moderately severe ambulatory paraparetic status. The ataxia will start in the rear legs and not be evident in the front legs until the rear legs are at least moderately ataxic. Acutely affected dogs typically are presented nonambulatory or at best weakly ambulatory.

The owner will complain of a wobbly unsteady gait in the rear legs and may notice that the dogs �knuckles over� on the rear feet. Affected dogs will generally have a low head and neck posture and resist extension of the cervical spine. Cervical pain is typically not present in these dogs, though a small number will exhibit mild cervical pain on neck manipulation. Dogs with CCSM tend to walk with a stiff stilted gait in the front legs.

Neurologic testing will vary depending on the severity of spinal cord compression. The typical dog will show proprioceptive placing, hopping, and hemiwalking deficits to the rear legs. Neurologic abnormalities to the front legs will be absent or less severe than to the rear legs other than for the more severely affected dogs. Neurologic deficits can be made worse by extending the neck. Myotactic reflexes will be normal to hyperreflexic to the rear legs. Myotactic reflexes to the front legs are typically normal, though they are hard to perform due to extensor tone. Because of the location of the compressive lesion(s) at C5-6 and C6-7, one would expect lower motor neuron reflexes to the front legs, but these typically are not apparent. Cross extensor reflexes will be present if the lesion is chronic.

A presumptive diagnosis of CCSM is made based on history, signalment, and neurologic signs. Referral of CCSM cases should be done as soon as possible to establish a definitive diagnosis and to allow surgical correction to be performed. A definitive diagnosis can only be made with myelography�if myelography can be performed, referral of these cases can be made after establishment of a definitive diagnosis.

The diagnostic workup that should be performed for suspected cases of CCSM includes plain radiographs of the cervical spine along with myelography and spinal fluid analysis. Myelography should include lateral, ventrodorsal, and linear traction views. Hyperextension views of the neck are discouraged because of the possibility of causing additional neurologic damage to the spinal cord. A spinal fluid analysis is performed to rule out inflammatory disease. Since most of these dogs are Doberman pinschers, screening for hypothyroidism and Von Willebrand's disease is also performed along with complete blood count and biochemical screening.

Plain film radiographs of dogs with CCSM may show narrowing of the disk space, spondylosis, shape changes to the vertebral body, and tipping of the vertebra. Tipping of the vertebrae is not a reliable indicator of where the lesion is located.(1) The lateral myelographic view will show a ventral compressive lesion most often located between C5�6 and/or C6�7. A dorsal compression of the spinal cord from the ligamentum flavum may also be present. A widening of the lateral dye columns may be seen on the ventrodorsal myelographic projection over the area of compression. The lateral traction myelographic view will demonstrate if the compressive lesion is dynamic or static in nature. Dynamic compressive lesions are present most of the time, while static lesions are uncommon in the middle-aged dog. If the compression of the spinal cord improves on linear traction, the lesion is considered a dynamic compressive lesion. If the compressive lesion does not improve on linear traction, it is considered a static form of compression. Different surgical treatments are required for correction of the problem, depending on whether the compression is static or dynamic.

The two methods of treating CCSM are medical therapy and surgery. Medical management is indicated only if the owner is unable financially or unwilling to have surgery performed, or if the animal has other major health problems which would preclude surgery. Medical management involves treating the dog with corticosteroids and exercise restriction; the procedure typically provides only temporary improvement. With time, the neurologic status of the medically treated patient tends to worsen.

For static ventral compressive lesions of the spinal cord, two surgical options are available. The first option is dorsal laminectomy over the offending area of compression. This procedure carries a significant chance of making the dog worse neurologically after surgery, at least on a temporary basis. The other choice is a ventral cervical decompression procedure similar to the procedure used to remove Hansen type 1 disk material. An inverted cone decompression technique (a modification of the standard ventral decompression technique) has been described for ventral decompression of the spinal cord to decrease the morbidity associated with the standard ventral decompressive procedure.(5)

For dynamic ventral spinal cord compression, a modified distraction-stabilization technique using an interbody polymethyl methacrylate plug is the author's procedure of choice.(4) This procedure uses a plug of polymethyl methacrylate to hold the vertebrae in a distracted position thus decompressing the spinal cord. A cancellous bone graft is placed along the ventral aspect of the vertebrae to cause a spondylosis of the vertebrae to occur.(4) Postoperatively, the dog is placed in a body cast for four to eight weeks to allow ventral fusion of the vertebrae to occur.

Postoperative care for dogs that have had the distraction-stabilization technique will depend on their neurologic status. Non-ambulatory dogs will require considerable nursing care, including keeping them dry and clean, making sure that they receive proper nutritional and fluid intake, and rehabilitation. Padded bedding such as egg-crate foam or waterbeds will help prevent decubital sores. Walking carts are invaluable in rehabilitation of these patients.(5) For ambulatory patients, food and water should be available in an elevated position because they cannot eat from a bowl on the floor. These dogs must also be restricted from use of stairs unless assisted, because of the risk of falling. Leash walking is encouraged to promote muscle development and coordination. Once the cast is removed, a harness is used instead of a collar for the rest of the dog's life.

Prognosis for dogs treated with the modified distraction-modification technique has been very good.(4) Ninety percent of the dogs had a successful outcome with this procedure, with 50% considered to be completely normal.(4) Three months is the average time to maximal improvement, though some dogs will take up to 10 months.(4) Dogs that are nonambulatory at the time of surgery have a poorer chance of optimal recovery than ambulatory dogs.(4) Dogs that are nonambulatory at the time of surgery usually will not return to a normal neurologic status, but have a reasonable chance of being a functional pet.

The Great Dane is the breed of dog most commonly affected with the vertebral malformation type of lesion. Other large breed dogs can also be affected with this form of the disease. This form of the Wobblers disease is seen in young dogs typically between 6�24 months of age. Clinically signs are slowly progressive and the owner may not initially recognize that a problem exists because they think that it is due to puppy clumsiness. Ataxia starts in the rear legs and may progress to affect the forelegs. The owner will complain of a wobbly incorodinate gait along with knuckling of the feet. The owner may also hear the nails scrap on the floor or sidewalk. Pain typically is not present. Neurologic testing will vary depending on the severity of spinal cord compression. The typical dog will show proprioceptive placing, hopping, and hemiwalking deficits to the rear legs. Neurologic abnormalities to the front legs will be absent or less severe than to the rear legs other than for the more severely affected dogs. Neurologic deficits can be made worse by extending the neck. Myotactic reflexes will be normal to hyperreflexic to the rear legs. Myotactic reflexes to the front legs are typically normal though they are hard to perform due to extensor tone. A presumptive diagnosis of Wobblers disease is made based on history, signalment, and neurological signs.

The diagnostic work-up is the same as for the middle aged dog with Wobblers disease. Plain radiographs, myelogram, and spinal fluid analysis should be performed. Other imaging techniques that are helpful are CT scans and MRI. Typically, multiple areas of spinal cord compression are identified in the cervical spine. Compression of the spinal cord is due to malformation of the vertebrae with secondary changes that further compromise the spinal cord. Abnormalities that are recognized include stenosis of the vertebral canal, malformation of the articular processes with degenerative changes, hypertrophy of the ligamentum flavum and joint capsule, and hypertrophy of the dorsal annulus fibrosis. Both dynamic and static lesions can be present. Rarely will compression be significantly improved with traction, however.

The goals of surgery are to decompress the spinal cord and counteract any inherent instability. Because of the typical annular nature of the compression, a dorsal laminectomy is performed. Under-cutting the sides of the lamina will free up the lateral side of the spinal cord. A dorsal laminectomy may lead to more instability due to the nature of the tissue removed or detached. Screw and wire fixation of the facets has been tried to offset the instability. Fusion of the disc space from a ventral approach can also be tried to eliminate the instability.� Historically, the prognosis for young dogs with Wobblers disease has not been good. At the University of Missouri, we have combined dorsal laminectomy, lag screw fixation of the facets, and ventral interbody fusion to correct these dogs. Early success has been encouraging.

References

1.  Seim HB, Withrow SJ: Pathophysiology and diagnosis of caudal cervical spondylomyelopathy with emphasis on the Doberman pinscher. J Am Anim Hosp Assoc 1982;18:241-251.

2.  Trotter EJ, deHaunta A, Geary JC, Brasner TH: audal cervial vertebral malformation-malarticulation in Great Danes and Doberman pinschers. J Am Vet Med Assoc 1976;168:917-930.

3.  VanGundy T: Canine Wobbler syndrome. Part 1. Pathophysiology and diagnosis. Compendium of Continuing Education 1989;11:144-157.

4.  Dixon BC, Tomlinson JL, Kraus KH: Modified distraction-stabilization technique using an interbody polymethyl methacrylate plug in dogs with caudal cervical spondylomyelopathy. J Am Vet Med Assoc 1996;208(1):61-68.

5.  Goring RL, Beale BS, Faulkner RF: The inverted cone decompression technique: A surgical treatment for cervical vertebral instability �Wobbler Syndrome� in Doberman pinschers. Part 1. J Am Anim Hosp Assoc 1991;27:403-409.

6.  Vaughan RW, Short SJ, Kirkland KD: Construction of a cart and sling for rehabilitation of immobile dogs. Vet Med/Small Anim Clin, February, 1983;191-194.