[Diagnostic evaluation and differential diagnosis of primary hyperparathyroidism]

Primary hyperparathyroidism (PHPT) is characterized by the autonomous production of parathyroid hormone (PTH), in which there is hypercalcemia or normal-high serum calcium levels, in the presence of elevated or inappropriately normal serum PTH concentrations. Exceptionally, in symptomatic patients, a diagnosis can be established on the basis of clinical data. PHPT must always be evaluated in patients with clinical histories of nephrolithiasis, nephrocalcinosis, osseous pain, subperiosteal resorption, and pathologic fractures, as well as in those with osteoporosis-osteopenia on dual-energy X-ray absorptiometry (DEXA), a personal history of neck irradiation, or a family history of multiple endocrine neoplasia syndrome (types 1 or 2). Diagnosis of PHPT is biochemical. Asymptomatic hypercalcemia (total serum calcium corrected by albumin), without guiding signs or symptoms, is the most frequent manifestation of the disease. For the differential diagnosis, PTH(1-84) must be measured, as well as phosphate, chloride, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and calcium-to-creatinine clearance. Suppressed or inappropriately low PTH1-84 guides the diagnose toward tumoral hypercalcemia and less frequently to granulomatous disease (sarcoidosis, tuberculosis, etc.), inadequate intake of 1alpha-hydroxyvitamin D or calcitriol, vitamin D or A intoxication, lithium intake, endocrinopathies (hyperthyroidism, Addison's disease, etc.) or treatment with thiazides, among other possibilities. Diagnosis of PHPT is confirmed by demonstrating persistent hypercalcemia (or normal-high serum calcium levels) in the presence of inappropriately normal or elevated serum PTH(1-84) concentrations, unless the urinary calcium-to-creatinine clearance ratio is lower than 0.01. In these cases, in the absence of thiazide intake or severe vitamin D deficiency, diagnosis should focus on benign familial hypercalcemic hypocalciuria. Parathyroid gland imaging is useful for localization of PHPT, but not for diagnosis of this entity.