PTH and vitamin D deficiency: The diagnosis of nPHPT is established after exclusion of secondary causes of hyperparathyroidism, such as renal disease, vitamin D deficiency, malabsorption and dietary calcium deficiency or use of medications that may increase PTH level (i.e. bisphosphonates, denosumab, loop diuretics, antiepileptic drugs, lithium) (16), and virtually all of these conditions were excluded in our patients.