The natural history of treated and untreated primary hyperparathyroidism: the parathyroid epidemiology and audit research study.

Background: Primary hyperparathyroidism (PHPT) is a common endocrine disorder with the majority of cases being mild and untreated.

Aim: To provide an update on the natural history of treated and untreated PHPT.

Design: Retrospective population-based observational study.

Methods: From 1997 to 2006, a well-defined cohort of PHPT patients was established in Tayside, Scotland. Subsequent cohorts of 'mild untreated' and 'surgically treated' PHPT patients were selected for the present study. Their serum calcium (S-Ca) and PTH concentrations were followed until September 2009. Surgical outcomes were evaluated using hospital admission data.

Results: A total of 904 'mild untreated' patients were identified (median follow-up=4.7 years), with a baseline median S-Ca of 2.62 mmol/l. A general decreased trend was observed in the S-Ca concentration for up to 12 years but an increasing trend in PTH (P<0.001 in both instances). Disease progression, defined as an increase in S-Ca concentration, was observed in 121 patients (13.4%). Twenty-six (2.9%) patients had undergone surgery during the subsequent follow-up period. Baseline age and PTH concentration were the only significant risk factors for disease progression. In comparison, there were 200 'surgically treated' patients (median follow-up=5.8 years). S-Ca was normalised after surgery, in 196 patients (98%). Hospital admissions for renal complications were reduced after surgery. In conclusion, most untreated patients with mild PHPT had no progression of S-Ca but approximately 15% did show some evidence of progression. Parathyroidectomy, with a high success rate, normalized the S-Ca in patients with PHPT.