The Myth of Fibroid Degeneration in the Canine Intervertebral Disc: A Histopathological Comparison of Intervertebral Disc Degeneration in Chondrodystrophic and Nonchondrodystrophic Dogs.

Since the seminal work by Hans-Jörgen Hansen in 1952, it has been assumed that intervertebral disc (IVD) degeneration in chondrodystrophic (CD) dogs involves chondroid metaplasia of the nucleus pulposus, whereas in nonchondrodystrophic (NCD) dogs, fibrous metaplasia occurs. However, more recent studies suggest that IVD degeneration in NCD and CD dogs is more similar than originally thought. Therefore, the aim of this study was to compare the histopathology of IVD degeneration in CD and NCD dogs. IVDs with various grades of degeneration (Thompson grade I-III, n = 7 per grade) from both CD and NCD dogs were used (14 CD and 18 NCD dogs, 42 IVDs in total). Sections were scored according to a histological scoring scheme for canine IVD degeneration, including evaluation of the presence of fibrocyte-like cells in the nucleus pulposus. In CD dogs, the macroscopically non-degenerated nucleus pulposus contained mainly chondrocyte-like cells, whereas the non-degenerated nucleus pulposus of NCD dogs mainly contained notochordal cells. The histopathological changes in degenerated discs were similar in CD and NCD dogs and resembled chondroid metaplasia. Fibrocytes were not seen in the nucleus pulposus, indicating that fibrous degeneration of the IVD was not present in any of the evaluated grades of degeneration. In conclusion, intervertebral disc degeneration was characterized by chondroid metaplasia of the nucleus pulposus in both NCD and CD dogs. These results revoke the generally accepted concept that NCD and CD dogs suffer from a different type of IVD degeneration, in veterinary literature often referred to as chondroid or fibroid degeneration, and we suggest that chondroid metaplasia should be used to describe the tissue changes in the IVD in both breed types.

Inflammatory profiles in canine intervertebral disc degeneration.

BACKGROUND: Intervertebral disc (IVD) disease is a common spinal disorder in dogs and degeneration and inflammation are significant components of the pathological cascade. Only limited studies have studied the cytokine and chemokine profiles in IVD degeneration in dogs, and mainly focused on gene expression. A better understanding is needed in order to develop biological therapies that address both pain and degeneration in IVD disease. Therefore, in this study, we determined the levels of prostaglandin E2 (PGE2), cytokines, chemokines, and matrix components in IVDs from chondrodystrophic (CD) and non-chondrodystrophic (NCD) dogs with and without clinical signs of IVD disease, and correlated these to degeneration grade (according to Pfirrmann), or herniation type (according to Hansen). In addition, we investigated cyclooxygenase 2 (COX-2) expression and signs of inflammation in histological IVD samples of CD and NCD dogs. RESULTS: PGE2 levels were significantly higher in the nucleus pulposus (NP) of degenerated IVDs compared with non-degenerated IVDs, and in herniated IVDs from NCD dogs compared with non-herniated IVDs of NCD dogs. COX-2 expression in the NP and annulus fibrosus (AF), and proliferation of fibroblasts and numbers of macrophages in the AF significantly increased with increased degeneration grade. GAG content did not significantly change with degeneration grade or herniation type. Cytokines interleukin (IL)-2, IL-6, IL-7, IL-8, IL-10, IL-15, IL-18, immune protein (IP)-10, tumor necrosis factor (TNF)-α, and granulocyte macrophage colony-stimulating factor (GM-CSF) were not detectable in the samples. Chemokine (C-C) motif ligand (CCL)2 levels in the NP from extruded samples were significantly higher compared with the AF of these samples and the NP from protrusion samples. CONCLUSIONS: PGE2 levels and CCL2 levels in degenerated and herniated IVDs were significantly higher compared with non-degenerated and non-herniated IVDs. COX-2 expression in the NP and AF and reactive changes in the AF increased with advancing degeneration stages. Although macrophages invaded the AF as degeneration progressed, the production of inflammatory mediators seemed most pronounced in degenerated NP tissue. Future studies are needed to investigate if inhibition of PGE2 levels in degenerated IVDs provides effective analgesia and exerts a protective role in the process of IVD degeneration and the development of IVD disease.

"Disk extension beyond the interspace": an investigation into an alternative nomenclature in diagnostic imaging for displaced canine intervertebral disk material.

BACKGROUND: Displacement of canine intervertebral disk material can be seen directly in diagnostic imaging modalities such as magnetic resonance imaging and computed tomographic imaging. Canine intervertebral disk herniation can be differentiated into Hansen type 1 and 2 categories by clinical appearance, but anular- and nuclear disk material cannot be distinguished in computed tomographic images. Therefore, we hypothesized that the "Disk extension beyond the interspace"-nomenclature that describes the displacement by the disk contour might aid diagnosis. The aim of this study was to test the reliability of the "Disk extension beyond the interspace"-nomenclature in the evaluation of canine intervertebral disks via magnetic resonance and computed tomographic imaging. RESULTS: Magnetic resonance and computed tomographic images of 144 intervertebral disks of 43 dogs were evaluated by 3 observers with different degrees of experience from 2 institutions retrospectively. A substantial intraobserver agreement was found, while interobserver agreement was fair to moderate with significant differences in evaluation. Comparison of imaging methods showed a fair to moderate agreement without statistically significant differences in evaluation. CONCLUSIONS: DEBIT-nomenclature cannot be recommended for veterinary clinical usage yet. The largest variability was found in the evaluation of the bulged canine intervertebral disk. The observers' experience and the imaging method influenced DEBIT- evaluation only slightly, while training and working at different institutions influenced DEBIT-evaluation strongly.

Intervertebral disc disease in dogs - part 2: comparison of clinical, magnetic resonance imaging, and histological findings in 74 surgically treated dogs.

The relationship between intervertebral disc (IVD) disease and IVD degeneration remains unclear. The aim of the present study was to compare the clinical severity of IVD herniation (IVDH), determined with a neurological grading system, with findings of magnetic resonance imaging (MRI) and histology using grading systems for IVD degeneration in chondrodystrophic (CD; n=37) and non-chondrodystrophic (NCD; n=37) dogs. This study is the second part of a two-part investigation, where the first part involved the development and validation of a histological grading scheme for classification of canine IVD degeneration. IVD degeneration graded on MRI correlated significantly with IVD degeneration graded on histology, but not with pre-operative clinical signs. Hansen type 1 hernias were more common in the cervical and thoracolumbar segments and Hansen type 2 hernias were more common in the lumbosacral segment. Type 1 hernias occurred more often in CD dogs than in NCD dogs, and CD dogs were clinically more severely affected than NCD dogs. The grade of IVD degeneration on MRI was higher in CD dogs than in NCD dogs, but there was no difference between dogs with type 1 and type 2 hernias. No significant differences in histological grade were found between CD and NCD dogs or between type 1 and type 2 hernias. It was possible to conclude that IVD degeneration did not correlate with the neurological severity of IVDH. The extent of degeneration identified on MRI correlated with degeneration seen histologically. Although the MRI grading system reflected the severity of IVD degenerative changes as confirmed by histopathology, it appeared less useful in predicting the clinical implications.

Cytologic and histopathologic evaluation of extruded canine degenerate disks.

OBJECTIVE: To describe the cytologic and histopathologic appearance of degenerate disk material in dogs with Hansen type I intervertebral disk disease (IVDD). STUDY DESIGN: Case series. ANIMALS: Dogs (n=45) that had surgical intervention for Hansen type I IVDD (January-November 2007). METHODS: Impression smears and histopathologic sections were prepared from surgically removed degenerate disk material. All slides were evaluated for overall cellularity, quantity and attributes of extracellular matrix, types of cells present, and their cytomorphology. Histopathologic sections were also examined for presence of neovascularization and hemorrhage. RESULTS: Cytologically, 11 of 45 samples consisted of only extracellular matrix, 30 had evidence of inflammation, and 20 contained dysplastic spindloid cells. Histologically, hyaline cartilage predominated in 35 of 45 samples, fibrocartilage in 4, and spindloid cells in 6; 37 of 45 were inflamed, 37 were hemorrhagic, and 13 had neovascularization. CONCLUSIONS: The cytologic and histopathologic appearance of extruded degenerate disk material in dogs is variable and can include dysplastic spindloid cells. CLINICAL RELEVANCE: The variability in cytologic findings and frequent presence of dysplastic spindloid cells suggest that cytology alone may not be a reliable tool to differentiate degenerate canine disk material from a mesenchymal neoplasm.