SAN FRANCISCO – Neck irradiation of children and adolescents appears to increase their risk of later parathyroid adenoma as well as thyroid carcinoma, doctors at the University of California at San Francisco have reported.
At a regional clinical research meeting, Dr. Michael D. Okerlund said the prevalence of parathyroid adenoma in such patients is 100 to 1,000 times that cited in published studies of the U.S. population.
An assistant professor of radiology, Dr. Okerlund arrived at that estimate after a prospective study of 300 people evaluated primarily for thyroid disease disclosed parathyroid adenomas in eight and a parathyroid carcinoma in another. Three additional patients are being observed for possible parathyroid lesions because elevated parathyroid hormone levels and hypercalcemia were discovered during their initial screenings.
In a control group of 112 people with no history of neck irradiation, only one was found to have an elevated calcium level. Another had an elevated serum parathyroid hormone level, Dr. Okerlund reported, but that finding was not confirmed in a repeat study.
The prospective investigation was prompted by the chance finding of a parathyroid adenoma in a woman who developed a thyroid nodule 32 years after neck irradiation. Next, 55 patients operated on for primary hyperparathyroidism were interviewed. Among that group, said Dr. Okerlund, UCSF surgeons found 19% had a positive radiation history, and 17% more had a history of diseases for which neck irradiation was commonly given. The most frequent radiation sites were skin (for acne), tonsils, adenoids, and cervical lymph nodes.
The latent interval appears to be longer than the ten-to-20-year average for thyroid lesions. Parathyroid disease, in Dr. Okerlund’s study, was found in patients between 40 and 50 years of age. Radiation doses in those with parathyroid lesions ranged between 400 and 935 rads.
Serum calcium should be included in thyroid studies of all patients with a remote history of neck irradiation, Dr. Okerlund concluded, and radiationinduced parathyroid tumors should be sought in those with hypercalcemia, kidney stones, or related symptoms.