Introduction

• A developmental condition of well-fed foals and young horses, especially male Thoroughbreds.
• Condition may have hereditary component.
• Cause: abnormalities in the vertebral bodies, dorsal lamine and/or articular processes   →   dynamic or static stenosis of the vertebral canal   →   focal compression of the spinal cord.
• Signs: gait abnormalities, proprioceptive abnormalities and weakness.
• Diagnosis: neurologic examination, plain radiography, and contrast myelography of the trunk and limbs, computed tomography, ruling out other causes of neurologic disease.
• Treatment: conservative or surgical depending upon severity of condition.
• Prognosis: dependent on severity of neurologic signs and intended use of horse.

Pathogenesis

Pathophysiology

• Progressive spinal cord compression   →   clinical signs.
• Osteochondrosis-like lesions have been seen on the articular surfaces and vertebral body growth plates in some affected horses.
• 2 syndromes are seen: dynamic stenosis and static stenosis.

Dynamic stenosis

• Extension or flexion of neck   →   compression.
• C3-C4 most commonly affected site, followed by C4-C5.
• Seen mostly in weanlings, yearlings and 2 year-olds. Most commonly diagnosed between 8 and 18 months.
• Radiographs taken in neutral position may appear normal.

Static stenosis

• Stenotic canal always present, but may be exacerbated by flexion or extension.
• C5-C7 usually affected.
• Wedging of cranial aspects of vertebral bodies   →   narrowing of vertebral canals   →   cord compression.
• Malformation of articular processes and remodeling of intervertebral joints   →   cord compression.
• Horses 1-4 years old, often diagnosed in training; can also be diagnosed in horses 5-10 years of age.
• Soft tissue compression secondary to synovial proliferation.
• Damage to ascending spinal cord tracts   →   proprioceptive abnormalities on all four legs   →   manifest as ataxia (occasionally as hypermetria).
• Damage to descending spinal cord tracts   →   tetraparesis (particularly evident on doing a 'tail pull'), stiffness or hypometria.

Timecourse

• Variable.
• Usually progressive.
• Onset may be acute (traumatic incident) or insidious.
• Confirmed cases rarely resolve spontaneously.

Epidemiology

• Thoroughbreds and Quarterhorses most commonly affected.
• Males overrepresented.

Diagnosis

Treatment

Outcomes