To the Editor: Dr Imaizumi and colleagues1 reported a dose-response relationship between radiation exposure and thyroid disorders using data from a cohort of atomic bomb survivors from Hiroshima and Nagasaki. The strengths of this study include the large population and the accurately defined exposure estimates and end points.
More sophisticated methods to precisely define thyroid disorders might accurately detect radiation effects on the thyroid for diseases other than malignancies. While dose-response associations of radiation exposure with thyroid malignancies, benign nodules, and cysts were consistent over a number of analyses, Imaizumi et al found no significant relation between exposure to radiation and positive levels of antithyroid peroxidase antibody (TPOAb). In their study, a TPOAb cutoff of 10 IU/mL was chosen to define positivity. However, no justification for this choice was given.
Reference values provided by manufacturers might not be sufficiently specific to accurately define autoimmune thyroid disease, and definitions of positive TPOAb levels based on higher cutoffs might have been useful. For example, we found a statistically significant relationship between occupational exposure to ionizing radiation and autoimmune thyroid disease by using TPOAb cutoffs that were at least twice as high as the manufacturer's recommendation.2 While the inclusion of TPOAb in the definition of autoimmune thyroid disease was useful in the subpopulation of women, our data also have indicated that TPOAb levels were less suitable to describe the radiation-related risk of autoimmune thyroid disease among males compared with hypoechogenicity in thyroid ultrasound.2
Given the general variability of TPOAb methods and that diffuse reduction in thyroid echogenicity indicative of lymphocytic infiltration is often seen before TPOAb can be detected,3 it would be of interest if the authors could analyze their data using ultrasound markers of autoimmune thyroid disease as alternative dependent variables.
Financial Disclosures: None reported.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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