Normocalcemic primary hyperparathyroidism
Normocalcemic primary hyperparathyroidism (NC-PHPT) is a condition characterized by normal albumin-adjusted total serum calcium or ionized calcium and persistently elevated serum PTH. Therefore, to recognize this entity it is necessary to measure PTH in normocalcemic individuals. The question arises why would someone measure PTH in a normocalcemic subject? A pro-active approach to women evaluated in their early postmenopausal years for parameters of skeletal health as well as the attitude of measuring PTH in all subject undergoing evaluation for low bone mineral density may at least partially answer this question. In the diagnostic workup vitamin D status should be firstly evaluated. Indeed vitamin D insufficiency (25OHD levels below 30 ng/ml) is a rather common condition and often account for elevated PTH levels. Patients with low 25OHD should be replaced with vitamin D and reevaluated. Occasionally these patients will become hypercalcemic, thus unmasking the more typical hypercalcemic PHPT. If PTH remains elevated following vitamin D repletion, all other causes of secondary hyperparathyroidism, such as liver disease, renal disease, significant hypercalciuria (urinary calcium >350 mg/24 h), and gastrointestinal disease associated with malabsorption, or other metabolic bone disease that could affect PTH levels (e.g. Pagets disease) should been considered and ruled out. Patients taking drugs which might affect PTH levels (lithium carbonate, thiazide diuretics) or calcium metabolism (estrogens, loop diuretics, bisphosphonates, and anticonvulsants) should be reevaluated after drug withdrawal. The natural history of NC-PHPT is unknown, but observational studies provided evidence that some individuals may develop hypercalcemia or evidence of disease progression with development of kidney stones, decline of bone mineral density, fractures, marked hypercalciuria. The current evidence indicates that NC-PHPT is a real clinical entity, which has been recognized at the 3rd International Workshop on the Management of Asymptomatic PHPT as a variant of PHPT.
Declaration of interest: The author declares that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.