Ultrastructural Changes in Otoconia of Osteoporotic Rats

Abstract

The etiology of benign paroxysmal positional vertigo (BPPV) remains obscure in many cases and women are affected more often than men. A recent prospective study, performed in women >50 years of age suffering from recurrent BPPV, showed associated osteopenia or osteoporosis in a large percentage of these patients. These results suggested the possible relationship between recurrent BPPV and a decreased fixation of calcium in bone in women >50 years. To test this hypothesis, an experimental study was performed in adult female rats. Utricular otoconia of female rats in which osteopenia/osteoporosis was induced by bilateral ovariectomy (OVX) were compared to those of sham-operated adult females rats (SHAM), as control group. First Study: The morphology of theutricles of OVX and SHAM rats was analyzed with scanning electron microscopy. In osteopenic/osteoporotic rats, the density of otoconia (i.e. the number of otoconia per unit area) was decreased (p = 0.036)and their size was increased (p = 0.036) compared to the control group. Second Study: To test the role of calcium turnover in such morphological changes, utricular otoconia of 2 other groups of OVX and SHAM rats, previously injected with calcein subcutaneously, were examined by conventional and epifluorescence microscopy. In epifluorescence microscopy, labeling with calcein showed no significant fluorescence in either group. This finding was interpreted as a lack of external calcium turnover into otoconia of adult female rats. The ultrastructural modifications of otoconia in osteopenic/osteoporotic female adult rats as well as the role of estrogenic receptors in the inner ear are discussed. The possible pathophysiological mechanisms which support the relationship between recurrent BPPV in women and the disturbance of the calcium metabolism of osteopenia/osteoporosis are debated.

The Role of Oxidative Stress and Inflammatory Mediators in Benign Paroxysmal Positional Vertigo

“…Finally, high-grade disintegration in the otoconia caused complete dissolution and fragmentation of calcium-rich material to the endolymph, creating the possible underlying cause of symptoms in BPPV. Vibert et al [16] also demonstrated that in ovariectomized rats, osteoporosis induction had created a less dense and less calcium-containing otoconia ultrastructure, which can be attributed to the development of BPPV. In addition to the ultrastructural and animal studies, clinical studies have also investigated the probable relationship between BPPV and calcium metabolism.…”

Bone mineral density and serum 25-hydroxyvitamin D in patients with idiopathic benign paroxysmal positional vertigo

“…Otoconia are in a dynamic state, and calcium is required for their mineralization and turnover [23,24]. Calcium and carbonate levels in the endolymph should be kept at critical level to initiate and maintain the mineralization of the otoconia protein matrix and avoid unnecessary mineralization [10,34,36]. It has been suggested that disturbance of calcium metabolism induced by osteoporosis/osteopenia can lead to BPPV.…”

“…It is well known that degradation and fragmentation of otoconiais an age-related process of demineralization, resulting in balance disorder [34,35]. The presence of osteoporosis or another systemic disease during aging may facilitate otoconial demineralization and detachment from the otoconial bed [34].…”

Analysis of Vitamin D and Calcium Levels in Benign Paroxysmal Positional Vertigo

“…This is supported by the fact that BPPV is more common especially in postmenopausal women aged >50 years, in whom osteopenia and osteoporosis are common. Such studies have suggested that osteoporosis and accordingly the Ca metabolism may be a risk factor for developing BPPV by affecting particularly the peripheral zone in otoconia, which have a similar structure with bone tissue (3). The role of vitamin D, which is directly related to Ca metabolism and bone formation, in BPPV has been concerned and the vitamin D levels of BPPV patients have been investigated.…”