Background: The introduction of routine measurement of serum calcium levels led to a sharp increase in the incidence of primary hyperparathyroidism in the early 1970s.
Objective: To evaluate the trends in the incidence of primary hyperparathyroidism since the mid-1970s.
Setting: Rochester and Olmsted County, Minnesota.
Design: Population-based descriptive study.
Patients: All residents of Rochester, Minnesota, who received an initial diagnosis of primary hyperparathyroidism between 1965 and 1992 were identified through the medical records linkage system of the Rochester Epidemiology Project. Included as persons having definite cases (92% of the total) were patients with pathologically confirmed hyperparathyroidism, hypercalcemia with inappropriately elevated parathyroid hormone levels, or hypercalcemia that had lasted for more than a year and had no cause other than primary hyperparathyroidism.
Measurements: Incidence rates were calculated and directly standardized to the population structure of white persons in the United States in 1990.
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 levels was added to the automated serum chemistry panel in July 1974, the incidence increased to 112 per 100 000 person-years in 1975 and then decreased somewhat, reflecting a sweeping effect. Despite improved case ascertainment, however, the incidence rate has continued to decrease; in 1992, the incidence was 4 per 100 000 person-years. A few patients had complications that might have been caused by hyperparathyroidism (22% between 1965 and June 1974 and 6% thereafter), and survival was not impaired in either period. The maximum serum calcium levels did not change (P = 0.15).
Conclusions: The progressive decrease in the incidence of primary hyperparathyroidism is unexpected and suggests a significant change in the epidemiology of this disease.