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      Radiation exposure and cytotoxic endocrinopathy: It is time for action

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          Abstract

          Unfortunate accidents such as the ones experienced in Chernobyl, Ukraine, in April 1986, and in Japan, in March 2011, remind us of the frailty of human life. As doctors, however, our work is not to just grieve for the victims of these mishaps, but rather to help them manage and overcome the medical consequences of such disasters. Terms like disaster management and disaster medicine relate to various health and medical aspects of caring for victims. Most of this work, however, is related to acute or subacute medical care, and tends to overlook the chronic sequelae that victims have to grapple with. Apart from acknowledging the more than 6000 cases of thyroid cancer in affected areas of Belarus, Ukraine and Russia, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) does not elaborate on the possible endocrinopathies linked with nuclear radiation exposure, an important group of illnesses which impair the quality of life of victims. One of the important medical conditions that may occur after exposure to nuclear irradiation is termed cytotoxic endocrinopathy.[1] Radiation has extensive, but differential, effects upon the endocrine system. The anterior pituitary is highly sensitive to radiation, with growth hormone secretion being the most vulnerable.[2] Irrespective of whether the damage is in pituitary or hypothalamic, growth hormone deficiency is universal (100%) in patients exposed to external radiotherapy (3750–4250 rads given in 15–16 fractions over 22 days). Deficiency of luteinizing hormone (LH), follicle stimulating hormone (FSH) (96%), adrenocorticotropic hormone (ACTH; 84%) and thyroid stimulating hormone (TSH; 49%), with hyperprolactinemia, can also occur.[3] In sharp contrast, the posterior pituitary exhibits extraordinary resilience to radiation exposure.[2] The hypothalamus is more prone to damage after radiation, as compared to the anterior pituitary. This may be due to hypothalamic neuronal damage, rather than reduced cerebral blood flow.[4] A paradoxical situation of precocious puberty, rather than gonadotropin deficiency, has been reported in girls with exposure to low doses of radiation (2500–4750 rads) for management of brain tumors.[5] It is thought that low-dose radiation disrupts the normal restraint of the central nervous system on the hypothalamus and accelerates pubertal growth. The thyroid gland is exquisitely sensitive to environmental thyroid disruptors, including irradiation. Thyroid cancers, especially papillary carcinoma and follicular tumors, which are more often >1.5 cm in diameter, multicentric, with local invasion and distant metastases, are common in patients with exposure to irradiation. Children are at higher risk, as reported from Belarus after the Chernobyl accident.[6] Benign abnormalities, such as focal hyperplasia, single or multiple adenomas, chronic lymphocytic thyroiditis, colloid nodules and fibrosis, may occur is up to 20–30% of an irradiated population.[7] Maximum work related to endocrinology seems to have been carried out in thyroidology after the Chernobyl incident. The Chernobyl Tumor Bank, set up in 1988, has identified over 95% of thyroid tumors as being of the papillary carcinoma variety.[8] A considerable rise in the incidence of thyroid cancer has also been reported from the Polish province of Opole, which suffered high levels of radiation exposure after the Chernobyl accident.[9] Similar findings have been noted in adult survivors of the atomic bombings of Hiroshima and Nagasaki.[10] The parathyroid seems to more resistant to radiation-induced cytotoxicity than its larger neighbor, the thyroid. However, individuals who have received neck irradiation should have their calcium level monitored, even though the latency period for development of hyperparathyroidism is very long (25–47 years).[11] The testes are very radiosensitive organs, and the damage may be irreversible or reversible. The degree of damage and the effect on Sertoli and Leydig cell function depends on the radiation dose, and the age and pubertal status of the boy.[12] The ovaries, is contrast to the testes, have a fixed population of oocytes which cannot be replaced. Hence, radiation-induced ovarian damage is usually permanent.[13] The adrenal gland seems relatively immune to radiation toxicity though its endocrine function involves steroidogenesis similar to that of the gonads. The reason for this is unclear.[2] With the recent incident in Fukushima, Japan, there has been a focused global attention on earthquakes, disaster preparedness, disaster management, nuclear energy and nuclear safety. Along with these issues, sufficient importance should also be devoted to the assessment and study of radiation-induced endocrinopathy or cytotoxic endocrinopathy. An article by Wiwanitkit in the current issue focuses on the important and timely topic of prophylaxis for radiation-induced thyroid dysfunction.[14] Another contribution by Niazi and Niazi highlights the importance of this topic as well.[15] The mechanism behind this group of diseases should be unraveled and appropriate management strategies designed to achieve optimal endocrine function for the people accidentally exposed to nuclear irradiation. The IJEM welcomes contributors and comments on this aspect of endocrinology and metabolism. As we remember the tragedy of Chernobyl, whose 25th anniversary falls on 26 April this year, let us contribute to improving the health of those affected by it and by similar such incidents. Let us sensitize our colleagues, and the world, to the importance of radiation-related endocrinopathy or cytotoxic endocrinopathy.

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          Most cited references16

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          Hypopituitarism following external radiotherapy for pituitary tumours in adults.

          The development of anterior pituitary hormone deficiencies has been studied in a group of 165 patients who underwent external radiotherapy for tumours of the pituitary or closely related anatomical sites, and who have been observed for up to 10 years. One hundred and forty had undergone pituitary surgery before radiotherapy. All patients received external radiotherapy by a three-field technique, giving 3750-4250 cGy in 15 or 16 fractions over 20-22 days. A combined test of anterior pituitary function using insulin hypoglycaemia or glucagon stimulation in conjunction with thyrotrophin and gonadotrophin releasing hormone tests and basal estimations of prolactin, thyroid hormones and testosterone or oestradiol was performed before radiotherapy. This was repeated six and 12 months later and subsequently annually. Before radiotherapy, 18 per cent of patients had normal growth hormone secretion, 21 per cent had normal gonadotrophin secretion, 57 per cent had normal corticotrophin reserve and 80 per cent had normal thyrotrophin secretion. Life table analysis demonstrated increasing incidences of all anterior pituitary hormone deficiencies with time: by five years all patients were growth hormone deficient, 91 per cent were gonadotrophin deficient, 77 per cent were corticotrophin deficient and 42 per cent were thyrotrophin deficient. At eight years, respective incidences of deficiencies were 100, 96, 84 and 49 per cent. Radiation-induced hyperprolactinaemia was seen in 73 patients; mean serum prolactin concentration rose from 227 +/- 11 mU/l to a peak of 369 +/- 60 mU/l at two years and subsequently declined towards the basal value. The primary diagnosis, patient age, sex, irradiated tissue volume and previous surgery were examined as variables that might influence the rate of development of anterior pituitary hormone deficiencies, but none of these factors had a significant effect. The radiation induced hyperprolactinaemia was however more marked in female patients. Although anterior pituitary hormone deficiencies most commonly developed in the order growth hormone, gonadotrophin, corticotrophin, thyrotrophin (61 per cent of patients), other sequences were evident. Most notably corticotrophin deficiency occurred before gonadotrophin deficiency. There is a high incidence of anterior pituitary hormone deficiencies in patients treated surgically for pituitary tumours and the incidence increases after external radiotherapy. Deficiencies may occur in an unpredictable sequence and endocrine testing is recommended on an annual basis.
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            Ovarian failure following abdominal irradiation in childhood: the radiosensitivity of the human oocyte.

            Ovarian function has been studied sequentially since 1975 in 19 patients treated in childhood for an intra-abdominal tumour with surgery and whole abdominal radiotherapy (total dose 30 Gy). Eleven patients received chemotherapeutic agents that are not known to cause gonadal dysfunction. All but one patient have developed ovarian failure with persistently elevated gonadotrophin levels (FSH and LH greater than 32 IU/litre) and low serum oestradiol values (less than 40 pmol/litre) before the age of 16 years. The majority (n = 12) did not progress beyond breast stage 1 without sex steroid replacement therapy. As the number of oocytes within the ovary declines exponentially by atresia from approximately 2,000,000 at birth to approximately 2000 at the menopause, we have been able to estimate that the LD50 for the human oocyte does not exceed 4 Gy.
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              The Chernobyl thyroid cancer experience: pathology.

              The Chernobyl accident was followed by a large increase in the incidence of thyroid carcinoma in the areas exposed to high levels of fallout. The Chernobyl Tumor Bank was set up in 1998 to make tumours available for study internationally, and a pathology panel reviewed all the tumours and established an agreed diagnosis. The thyroid tumours that were discovered after the Chernobyl nuclear accident were virtually all (95%) of the papillary carcinoma type. Rare examples of other tumour types were identified. Within the papillary group, several subtypes were noted, including classical or usual type, follicular variant, solid variant and mixed patterns Diffuse sclerosis variant, cribriform/morular type and Warthin-like variant were rare. No tall cell or columnar cell variants were identified. The tumours examined by the Pathology Panel of the Chernobyl Tumor Bank constitute a large representative sample (estimated at about 50%) of the tumours that developed in this population. This overview describes the method adopted by the panel and the different diagnostic categories adopted; illustrates the pathology of these neoplasms; compares the pathological characteristics of the early lesions with those identified after long latency periods and the institution of screening programmes and outlines the possible associated causes for the various morphological patterns seen. Copyright © 2011 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.
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                Author and article information

                Journal
                Indian J Endocrinol Metab
                IJEM
                Indian Journal of Endocrinology and Metabolism
                Medknow Publications (India )
                2230-8210
                2230-9500
                Apr-Jun 2011
                : 15
                : 2
                : 73-74
                Affiliations
                [1] Department of Endocrinology, BRIDE, Karnal, Haryana, India
                [1 ] Amrita Institute of Medical Sciences, Kochi, India
                [2 ] Growth and Diabetes Centre, Singapore
                Author notes
                Corresponding Author: Dr. Sanjay Kalra, BRIDE, Kunjpura Road, Karnal – 132 001, Haryana, India. E-mail: brideknl@ 123456gmail.com
                Article
                IJEM-15-73
                10.4103/2230-8210.81934
                3125010
                21731862
                9a336a51-5c61-4211-98cf-787a18cbfc07
                © Indian Journal of Endocrinology and Metabolism

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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                Endocrinology & Diabetes
                Endocrinology & Diabetes

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