Intervertebral disc disease in dogs - Part 1: A new histological grading scheme for classification of intervertebral disc degeneration in dogs

Three independent observers evaluated 35 IVDs at different stages of degeneration using the scheme. Glycosaminoglycan contents of the nucleus pulposus and macroscopic grading according to Thompson, which are considered 'gold standards' for IVD degeneration, were used to validate the scheme. Reproducibility was assessed by analysing the inter-observer reliability of all individual variables of the grading scheme, using a weighted kappa analysis. Significant correlations were found between Thompson grading and total histological score (r = 0.94; P < 0.01) and between glycosaminoglycan content and total histological score (r = -0.72; P < 0.01). Most individual histological variables showed 'moderate' to 'almost perfect' inter-observer reliability. The high correlation with the gold standards in combination with the high reproducibility indicates that the proposed histological grading scheme is reliable and objective for classification of IVD degeneration in both chondrodystrophic and non-chondrodystrophic dog breeds. (C) 2012 Elsevier Ltd. All rights reserved.