Occupational Exposure to Ionizing Radiation Is Associated with Autoimmune Thyroid Disease

In the August issue of the Journal (1) Volzke et al. claim that occupational exposure to ionizing radiation is associated with autoimmune thyroid disease (AITD). Since this is the first published study on this subject, Authors suggest that additional case-control studies are needed to confirm their findings. We are performing a study similar to that of Volzke et al reaching, however, opposite conclusions. In fact, we have data on 125 subjects (70 males and 55 females) exposed to ionizing radiations and on 125 controls of similar age (± 2 years) and of the same sex, never exposed to radiation. Both patients and controls worked in a large teaching hospital, and the study was performed in their working environment, so that accurate information about the cumulative dosage and time of exposure was obtained. Using the combined presence of a hypoechogenic thyroid echopattern and positive antithyroperoxidase antibodies (anti-TPO) levels for the diagnosis of AITD, we diagnosed the disorder in 3 female subjects in both groups (p=1), and in no male subject. No relationship between time of exposure or dosage and AITD was observed. In addition, we feel that the conclusion of Volzke et al is not justified by their own data. In fact, AITD was diagnosed in 3.3 % of exposed subjects (4 out of 120) and in 3.4% of the female population of controls (data on the prevalence of AITD in male control population are not given); among exposed males (representing two thirds of the whole exposed population) no subject had AITD; the prevalence of a hypoechogenic thyroid echopattern and positive anti-TPO levels was quite similar in the 2 groups: positive anti-TPO were found in 3.1% of exposed subjects and in 4.6% of non exposed ones, whereas a hypoechogenic pattern was detected in 8.1% and 7.3%, respectively. Last but not least, overt thyroid disorders were more frequent in non exposed subjects (10%) than in exposed ones (5.6%), barely missing statistical significance (p=0.07): should one infer that lack of exposure to radiation may be a risk factor for thyroid diseases other than AITD? In conclusion, on the basis of the present evidence, we disagree that workers exposed to ionizing radiation are at high risk for AITD. Nevertheless, the possibility of a marginal risk cannot be excluded, and further studies may be useful in this respect.