title: Immunoheterogeneity of parathyroid hormone in parathyroid cysts: diagnostic implications.
abstract: Parathyroid cysts are uncommon lesions of the neck leading to hypercalcemia in a significant percentage of cases. The distinction between parathyroid and thyroid cysts is difficult to make on a clinical basis alone and relies on the demonstration of elevated PTH levels in cyst fluid. We describe a case of a parathyroid cyst in which intact PTH (1-84) levels were misleadingly low while midmolecule 44-68 PTH was markedly elevated. To explain this discrepancy, we studied cyst fluid from this and two other patients using Sephadex G-75 gel chromatography. Fractions were analyzed using an immunoradiometric assay for intact hPTH (1-84) and a RIA specific for the midmolecular 44-68 region of hPTH. Immunoreactivity corresponding to hPTH (1-84) was absent in the first case but present in the remaining two. Immunoreactive peaks corresponding to PTH fragments were demonstrable in all three cyst samples. Patients with elevated hPTH (1-84) in cyst fluid were hypercalcemic; in contrast, the patient with a low cyst level of hPTH (1-84) was normocalcemic despite having markedly elevated levels of midmolecule PTH (44-68) in both serum and cyst fluid. Parathyroid cysts may thus produce fragments rather than intact PTH; reliance on an intact hPTH assay could lead to misdiagnosis. The measurement of PTH by a midmolecular assay may be preferable to the measurement of intact PTH in the evaluation of fluid from cystic neck masses.
authors.affiliation: UCLA School of Medicine, Department of Medicine 90024.
authors.forename: J
authors.initials: J
authors.lastname: Birnbaum
authors.forename: A J
authors.initials: AJ
authors.lastname: Van Herle
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002118:Calcium / Q000378:metabolism; D002850:Chromatography, Gel; D003560:Cysts / Q000175:diagnosis / Q000276:immunology* / Q000378:metabolism; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D010279:Parathyroid Diseases / Q000175:diagnosis / Q000276:immunology*; D010281:Parathyroid Hormone / Q000276:immunology / Q000378:metabolism; D013954:Thyroglobulin / Q000378:metabolism
chemical_list: D007457:Iodine Radioisotopes; D010281:Parathyroid Hormone; D013954:Thyroglobulin; D002118:Calcium