Clinical and Pathological Analysis of Epidural Inflammation in Intervertebral Disk Extrusion in Dogs

Abstract

Background: Little is known about the pathologic changes in the epidural space after intervertebral disk (IVD) extrusion in the dog.Objectives: To analyze the pathology of the epidural inflammatory response, and to search for correlations between this process and clinical findings.Methods: Clinical data from 105 chondrodystrophic (CD) and nonchondrodystrophic (NCD) dogs with IVD extrusion were recorded. Epidural material from these dogs was examined histopathologically and immunohistochemically. Using statistical analysis, we searched for correlations between severity of epidural inflammation and various clinical and pathologic variables.Results: Most dogs exhibited an epidural inflammatory response, ranging from acute invasion of neutrophils to formation of chronic granulation tissue. The mononuclear inflammatory infiltrates consisted mostly of monocytes and macrophages and only few T and B cells. Surprisingly, chronic inflammatory patterns also were found in animals with an acute clinical history. Severity of the epidural inflammation correlated with degree of the epidural hemorrhage and nucleus pulposus calcification (P = .003 and .040), but not with age, chondrodystrophic phenotype, neurologic grade, back pain, pretreatment, or duration. The degree of inflammation was statistically (P = .021) inversely correlated with the ability to regain ambulation.Conclusion and Clinical Importance: Epidural inflammation occurs in the majority of dogs with IVD extrusion and may develop long before the onset of clinical signs. Presence of calcified IVD material and hemorrhage in the epidural space may be the triggers of this lesion rather than an adaptive immune response to the nucleus pulposus as suggested in previous studies. Because epidural inflammation may affect outcome, further research is warranted.

Differences in Epidural Pathology between Cervical and Thoracolumbar Intervertebral Disk Extrusions in Dogs

“…Data of dogs with thoracolumbar IVD extrusion evaluated previously were used for comparison between cervical and thoracolumbar locations in the present study.…”

“…The following breeds were classified as CD: beagle, Cavalier King Charles spaniel, cocker spaniel, dachshund, English and French bulldog, Lhasa apso, Shi tzu, bichon frisé, basset hound, miniature schnauzer, Tibetan spaniel, Welsh corgi, Pekingese, and miniature poodle . The breed distribution of dogs presented to our hospital (2010–2016) was recorded, and percentages of individual breeds were calculated.…”

“…After primary damage of the spinal cord due to contusion and compression, a cascade of secondary events including hemorrhage, changes in intracellular ion concentrations, excitotoxicity, free radical production, and inflammation is triggered . These primary and secondary changes may affect different structures within the vertebral canal after IVD extrusion, including the epidural space . Although the basic pathophysiology is the same, clinical presentation and outcome differ considerably between thoracolumbar and cervical disk extrusions …”

“…Recently, we studied the epidural inflammatory response during thoracolumbar IVD extrusion by histologic and immunohistochemical techniques . Most dogs exhibited an epidural inflammatory response, ranging from acute invasion of neutrophils to chronic lesions with a mononuclear inflammatory pattern associated with connective tissue formation and vascular proliferation.…”

“…Therefore, the aims of this study were as follows: (1) to characterize the extruded IVD material and the inflammatory response in the epidural space histopathologically in dogs after cervical IVD extrusion by the same methods used in a previous study of thoracolumbar IVD extrusion; (2) to evaluate associations between epidural inflammation and clinical signs and specific histopathologic features; (3) to evaluate associations between histologic findings and the chondrodystrophic phenotype; and finally, (4) to compare these findings to those obtained in a previous study of thoracolumbar IVD extrusion …”