Applications from horses to the University of Kentucky Veterinary Diagnostic Laboratory over a 10-year period (2011-2021) for diagnoses of significant spinal diseases were inquired. A total of 426 cases have been identified. Disease distribution includes cervical vertebral myelopathy (n = 224), fracture/dislocation (n = 123), abnormal spinal curvature (n = 51), osteomyelitis (n = 13), intervertebral disc disease (n = 7), congenital anomalies of the spine (n = 5), and tumors (n = 3).
Spinal diseases associated with equine cervical stenosis (wobbler syndrome) make up the majority of cases. This is not surprising given the density of purebred horses in the central Kentucky area and the documented susceptibility of their bloodlines to the disease. Wobbler syndrome occurs when a deformity of the cervical vertebrae leads to narrowing of the spinal canal and compression of the cervical spinal cord. In general, wobbler syndrome is categorized as affecting two groups of horses. The first is young horses growing up with complex multifactorial interactions between sex, growth rate, diet, and genetic determinants. The second group is seen in older horses with age-related changes in the neck, particularly osteoarthritis. In this recall, males were most common (n = 182 males; n = 34 females), the mean age was 23.1 months (4–168 months), and Thoroughbreds were the most common breed (n = 165). Vertebrae are classified as irregular bones because of their complex shape. Therefore, changes in different places of the bones themselves can lead to compression of the spinal cord. Lesions of the articular process joints were the most common cause of spinal cord compression (n = 71) followed by subluxation of the vertebral body (n = 67), generalized narrowing of the canaliculus (n = 27), and thickening or elongation of the dorsal lamina (n = 13). Lesions of the articular process were largely due to osteoporosis, followed by osteonecrosis.
The cervical shaft was the most common site of fracture/subluxation (n = 69), with the vertebral body most frequently involved. In 11 cases, partial transection of the spinal cord was described. While a clinical history of trauma was reported in all of the identified cases, six had evidence of an underlying neurological disease (wobbler syndrome or primary equine myelitis).
Acquired spinal curvature disorders (such as scoliosis, lordosis or kyphosis) were identified in 51 cases, with 50 cases considered congenital and 1 case considered acquired. Among the congenital conditions, 71% had other skeletal abnormalities, including limb retraction or facial abnormalities. Dystocia was described in 66% of the histories provided. The thoracic column was the most common location (n = 27), followed by the lumbar column.
All cases of vertebral osteomyelitis occurred in horses under the age of one year. The lumbar spine was the most common location. Rhodococcus equi And the Streptococcus zooepidemicus were common bacterial isolates. A secondary pathologic fracture was observed in six cases.
Clinically significant intervertebral disc disease is an area of recent interest. In this review, cases of intervertebral disc disease showed yellowing of the disc material with varying degrees of fibrillation, fissure and loss. All cases had a clinical history of ataxia. Secondary spinal cord compression was observed in four cases.
Among the remaining disease categories, congenital anomalies of the spine included cystic vertebral body or vertebral fusion. Tumoral processes affecting the spine included primary vertebral body sarcoma, metastatic lymphosarcoma, and metastatic melanoma.
A variety of disease processes can affect a horse’s spine. Pathological evaluation of the equine spine in conjunction with clinical information will continue to aid a better understanding of these processes and their impact on equine health.
Editor’s note: This is an excerpt from the University of Kentucky’s Equine Science Review, Issue 21, published March 5, 2022. Jennifer Janes, DVM, PhD, Dipl. ACVP, associate professor of anatomical pathology at the University of Kentucky Veterinary Diagnostic Laboratory, provided this information. Source: January 2022 Seasonal equine disease.