Cervical Vertebral Malformation

Outline

Overview
Signalment
Signs
Causes and Risk Factors

BASICS

Overview

CVM causes ataxia owing to spinal cord compression. It is the most common cause of ataxia in horses in Europe and Australasia and is an important differential diagnosis in regions affected by inflammatory diseases such as EPM and WNV.

Signalment

CVM is reported to be due to either developmental bone disease (type 1 CVM) or secondary to osteoarthritis of the caudal cervical intervertebral joints (type 2 CVM), associated with older horses
There can be an overlap of these classifications. Affected horses are often large-framed, fast-growing horses
There likely is a genetic predisposition for the disease. Breeding trials involving both affected males and females have been unable to produce CVM cases but offspring did have a higher prevalence of osteochondritis dissecans lesions in other joints

Signs

Signs can be acute and include progressive paresis and ataxia
Because of the anatomy of the spinal cord initially signs will only be evident in the pelvic limbs, but eventually the thoracic limbs will be involved as well
The neurologic signs are due to proprioceptive and upper motor neuron deficits and are characterized by bilaterally symmetric knuckling of the fetlocks, toe dragging, swaying of the body when moving, dysmetria, a “floating” thoracic limb gait, circumduction of the outside pelvic limb when tightly circled, and the horse stepping on its own feet

Causes and Risk Factors

Type 1 CVM is likely a manifestation of DOD; cases have an increased incidence of DOD and osteochondrosis in other joints
Type 2 CVM is associated with significant arthropathies of the caudal cervical articular processes. External trauma and exercise are likely involved in the pathogenesis

Diagnosis ⬆ ⬇

Outline

Differential Diagnosis
Imaging

DIAGNOSIS

Differential Diagnosis

Cervical fractures—history and/or evidence of trauma. Cervical radiographs
EPM—CSF and serum antibody titers
Equine degenerative myeloencephalopathy—young animals with history of low vitamin E status
Equine herpesvirus 1—history of respiratory illness in other horses, cauda equina signs, viral identification using PCR or culture, CSF titers, CSF xanthochromia, rapidly progressive disease

Imaging

Standing plain film lateral cervical radiographs.

Type 1 CVM

Obvious vertebral malformation and malarticulation of the cervical vertebrae is common
Diagnosis is made by demonstrating a decreased diameter of the vertebral canal on lateral cervical radiographs
Myelography may contribute additional information and probably should be performed if the horse is going to surgery; however, it is rarely necessary in order to make the diagnosis

Type 2 CVM

The spinal cord in type 2 CVM is compressed secondary to osteoarthritis of the caudal (C6–T1) cervical vertebrae
Diagnosis made by showing enlarged and remodeled intervertebral joints of the caudal cervical vertebrae on radiographs, although the specificity of the technique is low due to many normal older horses having similar radiographic changes

Treatment ⬆ ⬇

TREATMENT

Conservative therapy—horses that are overtly ataxic will never recover completely but will become stronger with time. Owners must be counseled about the risk of injury to the handler even if the horse is retired to pasture. In very young animals with radiographic signs of CVM severe, long-term dietary restriction may be helpful; however, it is not recommended to attempt to ride any horses that have clinical signs so a neurologic examination must be passed before training could commence
Surgical—ventral cervical vertebral stabilization. This procedure uses a stainless-steel basket filled with cancellous bone graft to fuse the vertebrae. This has proved successful for both forms of CVM. The procedure is most successful in younger and mildly affected horses. Horses can take up to a full year to show improvement of neurologic deficits; some never fully recover but still become athletes. Owners should be aware that this is a long-term commitment and there are still liability issues involved if the horse is put into training

Medications ⬆ ⬇

MEDICATIONS

None indicated; corticosteroids give no long-term benefit.

Follow-up ⬆ ⬇

Outline

Prevention/Avoidance
Possible Complications
Expected Course and Prognosis

FOLLOW-UP

Prevention/Avoidance

Avoid overfeeding rapidly growing foals.

Possible Complications

Falling on rider and handler is a serious risk.

Expected Course and Prognosis

Once clinical signs are seen, prognosis for performance is grave unless surgery is undertaken
Mildly affected horses may be kept as pets as they may not progress; breeding type 1 CVM horses is strongly discouraged

Miscellaneous ⬆ ⬇

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