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Endocrine Care: Henry Völzke, André Werner, Henri Wallaschofski, Nele Friedrich, Daniel M. Robinson, Stefan Kindler, Matthias Kraft, Ulrich John, and Wolfgang Hoffmann Occupational Exposure to Ionizing Radiation Is Associated with Autoimmune Thyroid Disease J Clin Endocrinol Metab 2005; 90: 4587-4592 [Abstract] [Full text] [PDF]

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Re: Letter to the Editor

Henry Volzke, Andre Werner, Henri Wallaschofski, Nele Friedrich, Daniel M. Robinson, Stefan Kindler, Matthias Kraft, Ulrich John and Wolfgang Hoffmann   (5 October 2005)

Letter to the Editor

Luca Coppeta, Andrea Magrini, Antonio Pietroiusti, Umberto Iannaccone, Antonio Bergamaschi   (14 September 2005)

Re: Letter to the Editor 5 October 2005
Henry Volzke, MD Ernst Moritz Arndt University, Andre Werner, Henri Wallaschofski, Nele Friedrich, Daniel M. Robinson, Stefan Kindler, Matthias Kraft, Ulrich John and Wolfgang Hoffmann Send letter to journal: Re: Re: Letter to the Editor voelzke{at}uni-greifswald.de Henry Volzke, et al.	In their commentary Drs Coppeta, Magrini, Pietroiusti, Iannaccone and Bergamaschi have critically evaluated our recently published paper on the association between occupational exposure to ionizing radiation and autoimmune thyroid disease (AITD, 1). In their letter, they refer to data from a small retrospective cohort study showing no association between occupational exposure to ionizing radiation and AITD. Unfortunately, some relevant information is missing that would be needed to assess the context of the study and characteristics of the participants: 1) the regional level of iodine supply, as iodine deficiency is an important modulating factor for the relation between ionizing radiation and AITD (2); 2) the cumulative lifetime dosage of those exposed; 3) information regarding potential confounding risk factors, such as education and history of thyroid disorders in the exposed and the non-exposed group. Conflicting results between the study of Coppetta et al. and our report may further be related to the selection of exposed subjects. In a radiological setting, occupational exposure will predominantly–if not exclusively–be due to X- rays. This limits the comparability with our cohort where also nuclear power plant workers are included who were occupationally exposed to ß- and gamma-emitting radionuclides. We agree that the proportion of AITD among the exposed and non- exposed in our study was rather low. This was stated as a limitation of our study. However, the risk estimation for the association between the exposure to radiation and AITD was precise, consistent over a number of sensitivity analyses, and not affected by different categorizations of confounding risk factors. Coppeta et al. are also correct that there were lower proportions of subjects with prior history of thyroid disorders among those with occupational exposure to ionizing radiation compared to the non-exposed. It seems, however, far fetched to suggest that “the lack of exposure to radiation may be a risk factor for thyroid diseases other than AITD”. As listed in table 1 of our paper there were considerable differences in age, sex and smoking status between the exposed and the non-exposed explaining other differences found in the descriptive statistics. It is treacherous to draw conclusions from these bivariate tests as Coppeta et al. have done. The aim of our study was the investigation of possible associations between occupational exposure to ionizing radiation and AITD rather than between the exposure and known thyroid disorders. The latter would require a different statistical approach. Further high-quality studies conducted in large populations, however, are needed to confirm these findings and to prove the causal pathway. The use of thyroid protection shields by radiation workers is strongly recommended based on the precautionary principle. References 1. Volzke H, Werner A, Wallaschofski H, Friedrich N, Robinson DM, Kindler S, Kraft M, John U, Hoffmann W 2005 Occupational exposure to radiation is associated with autoimmune thyroid disease. J Clin Endocrinol Metab 90:4587-4592 2. Vermiglio F, Castagna MG, Volnova E, Lo Presti VP, Moleti M, Violi MA, Artemisia A, Trimarchi F 1999 Post-Chernobyl increased prevalence of humoral thyroid autoimmunity in children and adolescents from a moderately iodine-deficient area in Russia. Thyroid. 9:781-786.
Letter to the Editor 14 September 2005
Luca Coppeta, Professor University of Rome, Tor Vergata, Andrea Magrini, Antonio Pietroiusti, Umberto Iannaccone, Antonio Bergamaschi Send letter to journal: Re: Letter to the Editor antoniobergamaschi{at}tiscali.it Luca Coppeta, et al.	Dear Sir, 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. REFERENCE 1. Volzke H, Werner A, Wallaschofski H, Friedrich N, Robinson DM, Kindler S, Kraft M, John H, Hoffmann W 2005 Occupational exposure to ionizing radiation is associated with autoimmune thyroid disease. J Clin Endocrinol Metab 90: 4587-4592.