Presentation and Surgical Outcomes of Primary Hyperparathyroidism After Radioactive Iodine Therapy

Background: Radioactive iodine (RAI) is a common treatment for various thyroid diseases. Previous studies have suggested susceptibility of parathyroid glands to the mutagenic effect of RAI and the development of primary hyperparathyroidism (PHPT). We tested the possible link between prior RAI treatment, disease presentation, and treatment outcomes.

Methods: A retrospective analysis of 704 individuals who underwent parathyroidectomy for PHPT at a tertiary care center between the years 2015 and 2023 was performed. Preoperative and postoperative parameters, including demographic characteristics, biochemical markers, imaging data, and surgical and pathology findings were collected and analyzed to compare differences in patients who had previous RAI treatment and those who did not (non-RAI). Univariate statistical analyses were performed.

Results: Twenty-nine patients had a history of RAI treatment. Indications for RAI treatment included hyperthyroidism (n = 18), papillary thyroid cancer (n = 6), subacute thyroiditis (n = 1), follicular cancer (n = 1), and toxic goiter (n = 1). Average latency time between RAI exposure and development of PHPT was 18.4 ys. On comparison of the two groups, there was no difference in age, sex, race/ethnicity, day of surgery body mass index, preoperative parathyroid hormone, calcium, glomerular filtration rate, creatinine, vitamin D, or phosphate levels. There was also no difference in preoperative diagnosis of osteoporosis or nephrolithiasis. Postoperatively, there was no difference in parathyroid hormone, calcium, or creatinine levels, or in rate of cure. There was significantly higher chance of unilateral exploration in the operating room (75.9% RAI, 54.1% non-RAI, P = 0.02) and increased rate of single-gland disease in the RAI group, although the latter finding was not statistically significant (79.3% RAI, 65.2% non-RAI, P = 0.12). There was no difference in adenoma size as noted on the pathology report (greatest dimension 1.7 cm RAI, 1.7 cm non-RAI, P = 0.28). Subgroup analysis of the RAI group based on reason for RAI treatment (cancer versus hyperthyroidism) showed no statistically significant differences in the examined demographic or clinical data.

Conclusions: There does not seem to be a relationship between prior RAI treatment and the clinical presentation of PHPT. Additionally, differences in RAI dose do not appear to be associated with a change in clinical presentation. Our study revalidates that age and latency are inversely related, which is a previously shown finding. Clinicians may be reassured that patients with prior RAI history may not have differences in clinical characteristics, disease presentation, or treatment outcomes.