Otoconia degeneration as a consequence of primary hyperparathyroidism.

Abstract

Primary hyperparathyroidism (PHPT) is a common endocrine condition which disrupts physiologic calcium regulation. PHPT causes persistent hypercalcemia via the elevated and constant secretion of parathyroid hormone. Due to the effects of parathyroid hormone on target organs such as the bones, kidneys and gastrointestinal tract, untreated PHPT can lead to complications such as decreased bone mineral density, nephrolithiasis, and chronic abdominal pain, respectively. Given PHPT's drastic effect on calcium metabolism, it is likely that the condition also affects other organ systems, such as the inner ear, which rely on calcium for normal structure and function. Specifically, the saccule and utricle have otoconia made of calcium carbonate deposited on a protein framework. We hypothesize that PHPT, the epitome calcium disorder, can cause otoconia degeneration, one manifestation of which is benign paroxysmal positional vertigo (BPPV). As a preliminarily test of this hypothesis, we measured the levels of otolin-1, an inner ear glycoprotein found in the otoconia protein framework and a proposed biomarker for otoconia degeneration in patients with PHPT. We found a positive linear relationship between PTH (parathyroid hormone) and otolin-1 levels (R2 = 0.53) and total calcium and PTH levels (R2 = 0.32). These findings suggest that both PTH and total calcium levels affect otolin-1 levels, implying that the calcium dysregulation caused by PHPT may contribute to the otoconia breakdown and may be associated with inner ear disorders such as BPPV.