THE RISE AND FALL OF PRIMARY HYPERPARATHYROIDISM - A POPULATION-BASEDSTUDY IN ROCHESTER, MINNESOTA, 1965-1992

Background: The introduction of routine measurement of serum calcium l evels led to a sharp increase in the incidence of primary hyperparathy roidism in the early 1970s. Objective: To evaluate the trends in the i ncidence of primary hyperparathyroidism since the mid-1970s. Setting: Rochester and Olmsted County, Minnesota. Design: Population-based desc riptive study. Patients: All residents of Rochester, Minnesota, who re ceived an initial diagnosis of primary hyperparathyroidism between 196 5 and 1992 were identified through the medical records linkage system of the Rochester Epidemiology Project. Included as persons having defi nite cases (92% of the total) were patients with pathologically confir med hyperparathyroidism, hypercalcemia with inappropriately elevated p arathyroid hormone levels, or hypercalcemia that had lasted for more t han a year and had no cause other than primary hyperparathyroidism. Me asurements: Incidence rates were calculated and directly standardized to the population structure of white persons in the United States in 1 990. Results: From 1965 to June 1974 (the prescreening era), the age- and sex-adjusted incidence of primary hyperparathyroidism in Rochester was 15 cases per 100 000 person-years. After measurement of calcium l evels was added to the automated serum chemistry panel in July 1974, t he incidence increased to 112 per 100 000 person-years in 1975 and the n decreased somewhat, reflecting a sweeping effect. Despite improved c ase ascertainment, however, the incidence rate has continued to decrea se; in 1992, the incidence was 4 per 100 000 person-years. A few patie nts had complications that might have been caused by hyperparathyroidi sm (22% between 1965 and June 1974 and 6% thereafter), and survival wa s not impaired in either period. The maximum serum calcium levels did not change (P = 0.15). Conclusions: The progressive decrease in the in cidence of primary hyperparathyroidism is unexpected and suggests a si gnificant change in the epidemiology of this disease.