Acta Veterinaria Scandinavica 2007, 49:39 http://www.actavetscand.com/content/49/1/39 viously reported in radiographic [17,18] and MR [10] examinations in dogs. detectable calcification in affected discs represents the dis- tribution of a continuous variable. Radiographs and histological sections were each evalu- ated by one person, which means that both the radio- graphic and the histopathologic examination were subject to significant interobserver variation. With two or more persons evaluating the radiographs and the histological sections respectively, the interobserver variation and con- sequently the standard deviations of the observations pre- sented in Table 2, would decrease. Consequently, the calculated sensitivity of 0.6 represents an underestimate. At the radiographic examination, additional radiographs were taken if there was any doubt about calcification. At the histopathologic examination, at least two complete histological sections of each disc were examined to remove any doubt about calcification. By this, the present study should not be encumbered with significant intraob- server variation. A specificity of 1.0 indicates that no false-positive errors were made at the radiographic examination. The high technical quality of the radiographs is probably a signifi- cant reason for this. Another reason could be a reserved attitude by the reader of the radiographs, evaluating discs with uncertain calcification as negative. Von Kossa, a special stain for identification of calcium, was included in the histopathologic examination of all intervertebral discs. In previous histopathologic examina- tions of disc degeneration in dogs [4,10], this stain was not used. In the study by Seiler et al. [10], decalcification was also part of the preparation for histopathologic exam- ination. A discrepancy in results can easily arise when dif- ferent studies adopt different protocols. In the present study, histopathology was found consider- ably more sensitive than radiography in identifying calci- fied discs. Nevertheless, in ten discs the degree of calcification was found to be higher in radiography than in histopathology. A histopathologic examination of non representative sections could be an explanation for the different findings in these ten discs. Conclusion A histopathologic examination is superior to a radio- graphic examination in identification of calcified interver- tebral discs in the dachshund. A sensitivity of 0.6 and a specificity of 1.0 for radiography is calculated using number of calcified discs as parameter and histopathol- ogy as the gold standard. Calcification of the nucleus pul- posus and/or the annulus fibrosus is a significant sign of disc degeneration in dachshunds and the distribution of Competing interests The author(s) declare that they have no competing inter- ests. Authors' contributions ØS conceived of the study, carried out the radiographic examination and is the main author of the paper. ØK car- ried out the histopathologic examination. Both authors read and approved the final manuscript. Additional material Additional file 1 Table 3. Degree of calcification, evaluated by a radiographic and a his- topathologic examination in 26 intervertebral discs from each of 20 dachs- hunds. Degrees of calcification evaluated by radiography: light grey: slight. dark grey: moderate. black: severe. Degrees of calcification evalu- ated by histopathology: 1 slight. 2 moderate. 3 severe. Other note: -: intervertebral disc not available for a final histopathologic examination. Click here for file [http://www.biomedcentral.com/content/supplementary/1751- 0147-49-39-S1.doc] Acknowledgements We are grateful to Ms. Birgit Røe and Ms. Anne-Kristine Fevang for per- forming the histopathologic sections, to Dr. Agnar Kvellestad for practical help with photographic editing and to Dr. Monica Theresa Johnsen for lan- guage consultation. References 1. Seim HB: Thoracolumbar disk disease: diagnosis, treatment and prognosis. Canine Pract 1995, 20(1):8-13. 2. Priester WA: Canine intervertebral disc disease – occurrence by age, breed, and sex among 8.117 cases. Theriogenology 1976, 6:293-303. 3. Ball MU, McGuire JA, Swaim SF, Hoerlein BF: Patterns of occur- rence of disk disease among registered dachshunds. J Am Vet Med Assoc 1982, 180:519-522. 4. Hansen HJ: A pathologic-anatomical study on disc degenera- tion in dogs. Acta Orthop Scand Suppl 1952:1-117. 5. Havranek-Balzaretti B: Beitrag zur Aetiologie der Dackellähme und Vorschlag zur züchterischen Selektion. (The etiology of intervertebral disc disease in the dachshund and proposal of an eradication programme). Zürich: Veterinär-Chirurgischen Klinik und Institut für Veterinärpatologie. Dissertation, Universität Zürich; 1980. 6. Stigen Ø: Calcification of intervertebral discs in the dachs- hund. A radiographic study of 115 dogs at 1 and 5 years of age. Acta Vet Scand 1996, 37:229-237. 7. Stigen Ø: Calcification of intervertebral discs in the dachs- hund. A radiographic study 327 young dogs. Acta Vet Scand 1991, 32:197-203. 8. Stigen Ø, Christensen K: Calcification of intervertebral discs in the dachshund. An estimation of heritability. Acta Vet Scand 1993, 34:357-361. 9. Jensen VF, Christensen KA: Inheritance of disc calcification in the dachshund. J Vet Med A Physiol Pathol Clin Med 2000, 47:331-340. 10. Seiler G, Häni H, Scheidegger J, Busato A, Lang J: Staging of lumbar intervertebral disc degeneration in nonchondrodystrophic Page 6 of 7 (page number not for citation purposes)