Intervertebral disc disease (IVDD) is a major health problem in Dachshunds. Of all the dog breeds they have the highest incidence of IVDD, owing to their chrondrodystrophy and subsequent accelerated intervertebral disc (IVD) degeneration. Degenerated IVDs are predisposed to herniation, resulting in spinal cord injury and commonly paralysis. Late-stage IVD degeneration can include dystrophic calcification, and this calcification may be detected on spinal radiographs (radiographically detectable intervertebral disc calcification [RDIDC]). IVDD and RDIDC are highly heritable in Dachshunds, with RDIDC scores at young adult age being a strong predictor of clinical IVDD occurrence later in life. A screening program was developed whereby potential breeding candidates undergo spinal radiography and scoring for RDIDC, with the aim of reducing the incidence of IVDD through selective breeding. Despite the existence of a large body of literature around IVDD in Dachshunds, including a solid scientific basis for the development of the radiographic screening tool, several deficiencies and areas for ongoing research were identified and guided this project. Widespread global awareness and application of the screening program was lacking. Therefore, an extensive appraisal of the literature was performed resulting in the paper ‘Radiographic scoring for intervertebral disc calcification in the Dachshund’, which is available in the Veterinary Journal. For a test to be useful it must be precise, and the scorer variability (precision) for RDIDC scoring had not been evaluated. Accordingly, the within-scorer (repeatability) and between-scorer (reproducibility) variability of RDIDC scoring was estimated using five scorers with varying levels of prior experience, both at the individual IVD level and at the whole dog level for breeding classification purposes. Overall, RDIDC scoring was found to be highly consistent within scorers, with increased precision achieved by scorers with greater experience. However, unique individual scorer patterns were identified as a factor. These results supported the ongoing use of the screening program, and were published in Preventive Veterinary Medicine. Investigation of the utility of alternate diagnostic imaging modalities, namely computed tomography (CT) and magnetic resonance imaging (MRI), for scoring IVD calcification in Dachshunds had not previously been undertaken. The first step in evaluating these modalities for potential use was to assess scorer agreement for CT and MRI, and compare these results with radiography (i.e. RDIDC scoring). Supporting the results of prior work, radiography was identified as a highly precise test with repeatability and reproducibility estimates that were greater than for CT and MRI, likely attributable to scorer familiarity with the modality and RDIDC scoring. Again, increased scorer experience corresponded with greater RDIDC scoring precision. Despite these findings, CT identified substantially higher overall numbers of IVD calcifications than the other modalities, and further analysis of this data to examine the accuracy of the various modalities is warranted. Despite the work achieved through this project, ongoing research is needed. Additional experiments are planned, including analysis of the potential effect of instruction and training on RDIDC scorer subjectivity, and an epidemiological study of the Australian Dachshund population.Thesis (MPhil) -- University of Adelaide, School of Animal & Veterinary Sciences, 201
