Increased incidence of parathyroid adenomas following X-ray treatment of benign diseases in the cervical spine in adult patients

Summary Objective To determine whether or not exposure to ionizing radiation as an adult increases the risk of developing parathyroid adenomas. Design and Patients A cohort of 27 415 patients had received X‐ray treatment to palliate pain originating from arthrosis and spondylosis from 1950 to 1964. In a subcohort of 8144 patients the cervical spine was the target, or one of the targets for the treatment. With the technique used it could be assumed that, as a rule, the parathyroid glands had been included in the treated volume. Patients with parathyroid adenomas were obtained from the Swedish Cancer Register from 1958 to 1995. The standardized incidence ratio (SIR) was calculated. Results The number of person‐years at risk was 180 492 in the cohort exposed at the cervical spine, and 412 994 in the control cohort irradiated only at other sites. The calculated dose in the parathyroid region in the study cohort was about 1 Gy. The observed number of parathyroid adenomas in the study cohort was 22, and 24 in the control cohort. Expected numbers based on population data were 12·0 and 24·7, respectively, giving an SIR of 1·83 (95% CI 1·14–2·76) and 0·97 (CI 0·62–1·45), respectively. Mean age at exposure was 48·9 years (SD 10·2) and at diagnosis 71·5 years (SD 8·3). The time from exposure to diagnosis varied from 2 to 34 years (median 26 years). The excess relative risk was about 0·8 per Gy. Conclusion Exposure to ionizing radiation to the cervical spine in adult age seems to be associated with an increased risk of developing parathyroid adenomas.