Thyroid hypofunction,

Larsen PR, Conard RA, Knudsen K. Thyroid hypofunction appearing as a delayed manifestation of accidental exposure to radioactive fallout in a Marshallese population. In Biological Effects of Ionizing Radiation 1. Vienna International Atomic Energy Agency, 1978 101. 

SAFETY PROFILE Poison by ingestion, subcutaneous, and intraperitoneal routes. An experimental teratogen. Experimental reproductive effects. Human systemic effects blood pressure elevation, change in heart rate, coma, convulsions, diarrhea, hypermotility, pulse rate increase, thyroid hypofunction. When heated to decomposition it emits toxic fumes of I", NOx, and Na20. 

Thyroid Hypofunction Hypothyroidism is the most common disorder of thyroid function. It can be divided into patients who have a failure of the thyroid gland to produce sufficient thyroid hormone (primary hypothyroidism) and patients in which pituitary or hypothalamic disease is associated with impaired TSH stimulation (central or secondary hypothyroidism). Worldwide, primary hypothyroidism is caused most often by iodine deficiency. In areas where iodine is sufficient, chronic autoimmune thyroiditis (Hashimoto s thyroiditis) accounts for most cases. Other causes include postpartum thyroiditis, surgical removal, or radioactive iodine ablation of the gland. Hypothyroidism present at birth (cretinism) is the most common preventable cause of mental retardation in the world. 

Thyroid hypofunction is the most common hormonal deficiency in the general population (Roberts and Ladenson, 2004). The prevalence of hypothyroidism seems to rise with age, and is clearly higher in middle age and the elderly in relation to the younger population. However, hypothyroidism in aged people may go unnoticed because of its paucity of clinical manifestations, or because many of the chnical signs and symptoms are unspecific and may be confounded with the normal ageing process (Di ez, 1998). We herein review the main chnical aspects of this common condition in middle age and in the elderly. 

Post-operatory hypothyroidism is a consequence of partial or total thyroidectomy in patients with nodular goiters or thyroid tumors. This etiology was found in about one fourth of our patients. Patients with surgical procedures in the neck may also develop thyroid hypofunction, especially in cases in which surgery is combined with radiotherapy (Griffin, 1990). 

Iodine deficiency is the most common cause of hypothyroidism worldwide, but it is uncommon in developed countries where there is sufficient intake of iodine in the diet (Delange, 1998 Delange etal., 2001). Iodine administtation is another cause of thyroid hypofunction (AUen et al., 1986 ... 

Markou et aL, 2001), and this was the case in about 1% of our patients. Iodine excess inhibits iodine organification and T4andT3 synthesis (WoUf-Chaikoff effect). Normal subjects escape from this effect however, patients with abnormal thyroid gland do not and may develop thyroid hypofunction. Iodine also inhibits thyroid hormone release and decreases serum T4 and T3 levels (Woeber, 1991). Furthermore, iodine seems to be an important factor in thyroid autoimmunity in genetically predisposed individuals (Laurberg... 

Subacute thyroiditis exhibits easily recognizable clinical features. It is not a common cause of hypothyroidism in the elderly. Painless thyroiditis is also infrequent in aged people. These conditions may cause transient hyperthyroidism followed by a transient permanent thyroid hypofunction phase. Infiltrative diseases affecting the thyroid gland (Riedel s thyroiditis, hemochromatosis, scleroderma, leukemia, amyloidosis) and infections are rare causes of hypothyroidism at all ages. Toxic injury to the thyroid gland has been reported after exposure to polybrominated biphenyls and polychlorinated biphenyls (Roberts and Ladenson, 2004). 

Signs and symptoms usually associated with thyroid hypofunction in middle age and in the elderly are summarized in Table 106.2. Clinical presentation of hypothyroidism... 

Drugs that induce thyroid hypofunction iodine Lithium... 

Previous total or subtotal thyroidectomy for nodular goiter and the presence of an increase in serum TSH level indicate the diagnosis of post-operative hypothyroidism. Loss of thyroid function may also occur after definitive therapy for previous thyrotoxicosis, either with radioiodine or thyroidectomy. Some patients may exhibit a transient phase of thyroid hypofunction after partial thyroidectomy or radioiodine therapy with recovery of function. Other causes of hypothyroidism, such as thyroid dysgenesis, infiltrative diseases, iodine deficiency, iodine excess, painless thyroiditis and subacute thyroiditis are less common in the elderly and are usually easily recognizable by their clinical and analytical features. 

In most patients, cfinical history and physical examination and a fimited number of investigations are enough to diagnose the cause of thyroid hypofunction. 

Figure 107.1 Adequate control of hypothyroidism as a function of the duration of therapy. The relationship between duration of therapy (years) and the percentage of patients who showed adequate control of thyroid hypofunction in a cross-sectional study (a 385 patients) and in a follow-up study (b 56 patients). Figures in parentheses indicate the total number of patients in each group. Data from Dfez (2002). Reproduced with permission of the Gerontological Society of America.

In patients with known thyroid hypofunction and programed surgery, replacement therapy is indicated with the aim of attaining adequate control of thyroid hypofunction before an operation. Euthyroidism can be easily documented with the measurement of TSH as part of the pre-operative evaluation (Stathatos and Wartofsky, 2003). 

Note-. There is no agreement in the recommendations for screening of thyroid hypofunction in middie-aged and eideriy patients. Here we have summarized the opinions of some prestigious scientific societies. 

Biochemical Features A serum TSH elevation suggests primary hypothyroidism. A measurement of serum thyroxine (T4) (classically FT4) permits the classification of patients according to the severity of thyroid hypofunction OH when FT4 is below normal or SCH when it is normal... 

Recent reviews on the laboratory aspects of thyrotropin (TSH) assay have been published by Hall (H4) and Raud and Odell (Rl), so that it is only necessary here to discuss some aspects of the application of TSH assay. The key role of TSH in the control of thyroid secretion has been outlined in Section 2.4, and it is clear that TSH assays are of importance in the diagnosis of thyroid disorders, especially where thyroid hypofunction is involved. When combined with some form of stimulus, such as thyrotropin-releasing hormone (TRH), TSH levels are also useful in the investigation of thyrotoxicosis. 

On the basis of what has been said, there is only a suspicion of thyroid hypofunction. It is possible that a lowered activity may be ascertained by the use of more reliable thyroid tests. Further study of the problem is suggested. 

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