This report shows our conclusions on the clinical, biochemical and densitometry characteristics of 35 normocalcemic primary hyperparathyroidism (PHPT) patients. This condition is defined by a high level of intact parathyroid hormone (iPTHI) with persistently normal serum and ionized calcium in the absence of secondary hyperparathyroidism. Our selection consisted of 30 women (90%) and 5 men (10%). The control group of 55 hypercalcemic patients with primary hyperparathyroidism included 51 women (93%) and 4 men (7%). The average age at diagnosis of normocalcemic PHPT was 61.4 ± 11.7 years and 56.4 ± 11.3 years in hypercalcemic PHPT. Besides the expected differences in serum calcium, ionized calcium, phosphorus and 24 h urinary calcium, we found no significant changes in other biochemical variables, and no differences in densitometry evaluations such as the presence of osteopenia or osteoporosis and the number of fractures in the two types of PHPT. But there was a significant difference in the presence of renal lithiasis between normocalcemic PHPT (11.4%) and clasic PHPT (49.1%) p < 0.0005, to some extent associated to the presence of hypercalciuria in classic PHPT. Two of the 35 patients with normocalcemic PHPT became classic hypercalcemic PHPT over a 4 year follow-up period. Our findings support the hypothesis that the normocalcemic PHPT could be an early stage of the classic PHPT, both having similar clinical effects to metabolic renal and bone levels.
Keywords: calcemia; intact parathyroid hormone; ionic calcium; normocalcemic hyperparathyroidism.