Radiation-related thyroid autoimmunity and dysfunction

Abstract

The thyroid gland is vulnerable not only to external radiation but also to internal radiation, because the thyroid cells can incorporate radioactive iodine when synthesizing thyroid hormones. Since radiation-induction of thyroid neoplasia, including thyroid cancer, is well recognized, the data on radiation-related thyroid autoimmunity and dysfunction are summarized and reviewed. High-dose irradiation, irrespective of being external or internal, is strongly associated with a risk of hypothyroidism (with the prevalence ranging from 2.4% to 31%) and of Graves’ hyperthyroidism (with the prevalence being up to 5%). It is easy to understand that high-dose irradiation induces hypothyroidism with some frequency, because high-dose irradiation destroys the thyroid gland. On the other hand, the basis for development of hyperthyroidism is mechanistically unclear, and it is merely speculative that autoantigens may be released from damaged thyroid glands and recognized by the immune system, leading to the development of anti-thyrotropin receptor antibodies and Graves’ hyperthyroidism in subjects who are immunologically predisposed to this ailment. In contrast, the data on moderate to low-dose irradiation on thyroid autoimmunity and dysfunction are inconsistent. Although it is difficult to draw a definitive conclusion, some data may suggest a transient effect of moderate- to low-dose irradiation on hypothyroidism and autoimmune thyroiditis, implying that the effect, if it exists, is reversible. Finally, no report has shown a statistically significant increase in the prevalence of moderate- to low-dose irradiation–induced Graves’ hyperthyroidism.

Thyroid Sequelae of Pediatric Cancer Therapy

“…Although the mean time to primary hypothyroidism after craniospinal irradiation ranges from 1.5 to 6 years in the literature [46-48], hypothyroidism can occur years to decades after the diagnosis and treatment of cancer [9, 10](Fig. 1).…”

“…It is well-established that radiation can immediately cause transient thyrotoxicosis (followed by euthyroidism or hypothyroidism) via direct destruction of the thyroid parenchyma (so called destructive or radiation-induced thyroiditis) when the thyroid gland is directly within the field of irradiation [10, 21, 78]. This is usually subclinical in nature and typically not identified since thyroid function tests (TFTs) are not routinely checked during or shortly after radiotherapy is given.…”

“…As a late effect, hyperthyroidism has been reported to occur in 0.3–4.6% of cancer (predominantly Hodgkin lymphoma and leukemia) survivors [10, 20-22, 24, 26, 57, 79, 80]. In the study by Sklar et al[26] in Hodgkin disease survivors, the risk of hyperthyroidism was eightfold greater than the incidence reported by sibling controls, and a thyroid radiation dose of ≥35 Gy was the main risk factor identified.…”

Hospital-based Analytical Study of Anti-thyroid Peroxidase Titre Among Type-2 Diabetic Patients Suffering from Thyroid Disorders

“…In spite of having associa on between type-2 diabetes and thyroid abnormality, clinicians s ll use an -TPO to lesser correlate with autoimmune disorders related to thryoidi s. Based on certain studies, one can use an -TPO as predictor [20][21][22][23] of thyroid abnormality in rela on to autoimmune disorders. So evalua on of an -TPO can play a significant role in determining appropriate diagnosis and clinical outcomes.…”

Progress in low dose health risk research

“…Supposedly, these immunomodulatory effects might have a bearing on IR induced carcinogenesis [102]. Immunemodulatory effects that differ at low, moderate and high doses are also thought to differently affect radiation-related thyroid autoimmunity and dysfunction [160].…”