Histopathological and morphometric study of cochleosaccular dysplasia in dalmatian dogs

Abstract

Problem: This study shows systematic morphometric and histopathologic analysis of temporal bones of Dalmatian dogs with cochleosaccular dysplasia at different ages in order to better understand the pathogenesis of cochleosaccular dysplasia. Methods: Three groups were selected: (1) deaf Dalmatians (1 month to 5 years); (2) 2 litters of Dalmatians from the same deaf female and same deaf male (1 day to 2 weeks); and (3) hearing age-matched Black Labradors (deafness not described in this breed). Measurements included stria vascularis and spiral ligament area counts, average density of spiral ganglion and Scarpa′s ganglion cells, and standard cytocochleograms. Reissner’s membrane (RM) was classified as normal, collapsed, or hydropic and saccules as normal or collapsed wall, and normal or abnormal otolitic membranes. Results: At 1 week, RM began to collapse close to limbus, but saccule appeared normal. By 10 days, RM and saccular wall were totally collapsed; however, saccular hair cells were preserved. After 1 week, all animals had abnormal otolitic membranes. There was total loss of hair cells in saccular macula in the 5-year-old. Spiral ganglion cells were lost in middle turn, followed by basal. Apical turn was affected only in the 5-year-old. Cochlear hair cells were present only during the first 2 weeks. Scarpa ganglion cells count showed that the normal dogs have more cells than the deaf group. Conclusion: Cochleosaccular dysplasia in this Dalmatian dogs seems to be a progressive disorder that begins with the collapse of Reissner’s membrane at the limbus followed by loss of hair cells and later the loss of spiral ganglion cells. Significance: Cochleosaccular dysplasia is considered the most common cause of profound congenital hearing impairment. Hereditary deafness in Dalmatian dogs generally appears isolated, as in human beings, making these dogs a good model for hereditary deafness. If the disease in human beings is also progressive, new therapeutic approaches could be evaluated to prevent the development of the disease. Support: None reported.