title: Substernal oxyphil parathyroid adenoma producing PTHrP with hypercalcemia and normal PTH level.
abstract: BACKGROUND
  Parathyroid adenoma is the most common cause of primary hyperparathyroidism. Preoperative serum calcium and intact-parathyroid hormone levels are the most useful diagnostic parameters that allow differentiating primary hyperparathyroidism from non-parathyroid-dependent hypercalcemia. Parathyroidectomy is the definitive treatment for primary hyperparathyroidism. Approximately 5% of patients who underwent parathyroidectomy present with persistent or recurrent hyperparathyroidism due to ectopic localization of the adenoma. Functioning oxyphil parathyroid adenoma is an uncommon histological form, seldom causing primary hyperparathyroidism. Parathyroid adenoma with hypercalcemia exhibiting normal parathyroid hormone level is rare. An incidence of 5% to 33% has been documented in the literature; no etiologic explanation has been given. In 1987, parathyroid-hormone-related peptide was isolated as a causative factor of humeral hypercalcemia of malignancy. The presence of parathyroid-hormone-related peptide in parathyroid tissue under normal and pathological conditions has been described in the literature; however, its role in causing hyperparathyroidism has not yet been defined.
  
  
  METHODS
  We present a case of persistent hypercalcemia with a normal level of intact-parathyroid hormone due to a substernal parathyroid adenoma, treated with radioguided parathyroidectomy. The final histological diagnosis was oxyphil adenoma, positive for parathyroid-hormone-related peptide antigens.
  
  
  CONCLUSIONS
  In clinical practice, this atypical biochemical presentation of primary hyperparathyroidism should be considered in the differential diagnosis of hypercalcemia. The parathyroid-hormone-related peptide should be considered not only in the presence of malignancy.
authors.affiliation: Department of Applications in Surgery of Innovative Technologies, University Medical School of Bari, Italy.angelagurrado@libero.it
authors.forename: Angela
authors.initials: A
authors.lastname: Gurrado
authors.forename: Andrea
authors.initials: A
authors.lastname: Marzullo
authors.forename: Germana
authors.initials: G
authors.lastname: Lissidini
authors.forename: Agostino
authors.initials: A
authors.lastname: Lippolis
authors.forename: Domenico
authors.initials: D
authors.lastname: Rubini
authors.forename: Gaetano
authors.initials: G
authors.lastname: Lastilla
authors.forename: Mario
authors.initials: M
authors.lastname: Testini
mesh_terms: D000236:Adenoma / Q000097:blood / Q000150:complications* / Q000175:diagnosis* / Q000473:pathology / Q000601:surgery; D000328:Adult; D006801:Humans; D006934:Hypercalcemia / Q000097:blood / Q000175:diagnosis / Q000209:etiology* / Q000601:surgery; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood*; D044162:Parathyroid Hormone-Related Protein / Q000097:blood*; D010282:Parathyroid Neoplasms / Q000097:blood / Q000150:complications* / Q000175:diagnosis* / Q000473:pathology / Q000601:surgery; D016105:Parathyroidectomy; D013249:Sternum
chemical_list: D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein