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Parathyroid hormone (PTH) disorders are characterized by a wide spectrum of clinical and biochemical presentations. The increasing use of serum PTH assay in the set of the diagnostic workout in patients with osteoporosis has identified patients with features of surgically confirmed primary hyperparathyroidism (PHPT) associated with persistent normal serum calcium levels, which has been recognized as a distinct entity from hypercalcemic PHPT (HPHPT) by the last international consensus. Normocalcemic PHPT (NPHPT) affects about 6–8% of PHPT patients. Although hypercalcemia is absent, patients with NPHPT experience kidney, bone, and cardiovascular impairments similar to those observed in HPHPT, suggesting that NPHPT may significantly affect the health of patients. Diagnosis of NPHPT requires an intensive diagnostic workup aimed to: (1) exclude all causes of secondary hyperparathyroidism, and (2) evaluate the occurrence of PTH-related diseases. The management of NPHPT is controversial in part due to lack of solid data about the natural history as well as the effects of surgical or medical treatments. Nonetheless, a clinical and biochemical follow-up is recommended in order to detect potential progression. When hypercalcemia and/or PTH-related disorders arise, parathyroidectomy can be considered. When surgery is not advisable, medical treatment aimed to increase bone mineral density may be a therapeutic option.

© 2019 S. Karger AG, Basel

Parathyroid hormone (PTH) is generating great interest as it is a master regulator of the bone metabolism and a marker of cardiometabolic risk. Though PTH has often been used as a marker for the differential diagnosis of hypercalcemic disorders, nowadays it is widely measured in normocalcemic subjects in the set of the diagnostic workflow for osteoporosis and bone metabolic diseases. In this context, most individuals have been diagnosed with normocalcemic primary hyperparathyroidism (NPHPT).

Fig. 1. Spectrum of parathyroid disorders according to serum calcium and PTH levels. ↑, increased; ↓, decreased; ◆, hypercalcemic disorders; ○ (small circles), normocalcemic disorders; ■, hypocalcemic disorders; ○ (large circle), NPHPT. SHPT, secondary hyperparathyroidism; hypo-PTH, hypoparathyroidism; hyper-PTH, hyperparathyroidism; pseudohypo-PT, pseudohypoparathyroidism; N, normal serum PTH levels. Dashed lines indicate the thresholds of serum PTH levels for the diagnosis of hypoparathyroidism (40.0 pg/mL) and hyperparathyroidism (65 pg/mL).

Primary hyperparathyroidism (PHPT) is sustained by autonomous PTH release from one or more parathyroid glands and includes a wide spectrum of clinical presentations (Fig. 1). Besides severe symptomatic and sometimes life-threatening hypercalcemia, PHPT often occurs with mild asymptomatic hypercalcemia. Symptoms related to hyperparathyroidism span throughout the different clinical presentations (Fig. 2). This wide spectrum includes NPHPT, which was firstly recognized in 2008 by the panel of experts of the Third International Workshop on Asymptomatic Primary Hyperparathyroidism [1], who positively answered the question: “Is normocalcemic hyperparathyroidism, which is defined as normal serum calcium with raised PTH in the absence of any common cause of secondary normocalcemic hyperparathyroidism, part of the diagnostic spectrum?”

Fig. 2. Spectrum of PHPT clinical presentations according to serum calcium levels; kidney and bone diseases are transversal to the different clinical presentations. The serum calcium threshold suggested as an indication for parathyroidectomy in asymptomatic PHPT by the most recent guidelines is reported. PTX, parathyroidectomy; eGFR, estimated glomerular filtration rate; FHH, familial hypocalciuric hypercalcemia; *, according the most recent guidelines [25].