Hashimoto s thyroiditis

Hypothyroidism, a condition in which the circulating concentrations of thyroid hormones are too low, is the most prevalent thyroid disease. Primary hypothyroidism, the commonest form, is an autoimmune disease (Hashimoto s thyroiditis) often associated with goitre. Like other autoimmune diseases, it is more prevalent in women (4 per 1000) than in men (1 per 1000). Other causes include thyroidectomy, radioac tive ablation and, in some countries, iodine deficiency. Hypothyroidism can also be caused by several drugs, including lithium, interleukin-2 and interferon. Secondary hypothyroidism is a disease caused by decreased secretion of TSH by the pituitary. 

The thyroid gland also regulates its uptake of iodide and thyroid hormone synthesis by intrathyroidal mechanisms that are independent of TSH. These mechanisms are primarily related to the level of iodine in the blood. Large doses of iodine inhibit iodide organification (Wolff-Chaikoff block, see Figure 38-1). In certain disease states (eg, Hashimoto s thyroiditis), this can inhibit thyroid hormone synthesis and result in hypothyroidism. Hyperthyroidism can result from the loss of the Wolff-Chaikoff block in susceptible individuals (eg, multinodular goiter). 

Hashimoto s thyroiditis Autoimmune destruction of thyroid Present early, absent later Mild to severe... 

The most common cause of hypothyroidism in the USA at this time is probably Hashimoto s thyroiditis, an immunologic disorder in genetically predisposed individuals. In this condition, there is evidence of humoral immunity in the presence of antithyroid antibodies and lymphocyte sensitization to thyroid antigens. Certain medications can also cause hypothyroidism (Table 38-5). 

The effectiveness of immunosuppressive drugs in autoimmune disorders varies widely. Nonetheless, with immunosuppressive therapy, remissions can be obtained in many instances of autoimmune hemolytic anemia, idiopathic thrombocytopenic purpura, type 1 diabetes, Hashimoto s thyroiditis, and temporal arteritis. Improvement is also often seen in patients with systemic lupus erythematosus, acute glomerulonephritis, acquired factor VIII inhibitors (antibodies), rheumatoid arthritis, inflammatory myopathy, scleroderma, and certain other autoimmune states. 

Reinhardt W, Luster M, Rudorff KH, Heckmann C, Petrasch S, Lederbogen S, Haase R, Sailer B, Reiners C, Reinwein D, Mann K. Effect of small doses of iodine on thyroid function in patients with Hashimoto s thyroiditis residing in an area of mild iodine deficiency. Eur J Endocrinol 1998 139(l) 23-8. 

Shibata H, Hayakawa H, Hirukawa M, Tadokoro K, Ogata E. Hypersensitivity caused by synthetic thyroid hormones in a hypothyroid patient with Hashimoto s thyroiditis. Arch Intern Med 1986 146(8) 1624-5. 

Nobuyuki Takasu, Masaki Takara, Ichiro Komiya. Rifampicin induced hypothyroidism in patients with Hashimoto s thyroiditis. N Engl J Med 2005 352(5) 518-9. 

Kifor et al. (2003) found autoantibodies to the CaR in four patients who had a clinical picture resembling that of FHH in the setting of other autoimmune conditions (e.g., Hashimoto s thyroiditis and sprue). The patients sera stimulated PTH secretion and inhibited high calcium-stimulated inositol phosphate accumulation and MAPK activation, presumably owing to antibody-mediated inhibition of the CaR. Further studies of a larger number of patients are required to determine the incidence of autoimmune, PTH-dependent hypocalciuric hypercalcemia in the presence of various types of autoimmunity. 

During the acute phase of a viral infection of the thyroid gland, there is destruction of thyroid parenchyma with transient release of stored thyroid hormones. A similar state may occur in patients with Hashimoto s thyroiditis. These episodes of transient thyrotoxicosis have been termed "spontaneously resolving hyperthyroidism." Supportive therapy is usually all that is necessary, such as propranolol for tachycardia and aspirin or nonsteroidal anti-inflammatory drugs to control local pain and fever. Corticosteroids may be necessary in severe cases to control the inflammation. 

Nontoxic goiter is a syndrome of thyroid enlargement without excessive thyroid hormone production. Enlargement of the thyroid gland is usually due to TSH stimulation from inadequate thyroid hormone synthesis. The most common cause of nontoxic goiter worldwide is iodide deficiency, but in the USA, it is Hashimoto s thyroiditis. Less common causes include dietary goitrogens, dyshormonogenesis, and neoplasms (see below). 

Hypothyroidism, known as myxedema in adults, when severe, is the most common disorder of the thyroid gland. Worldwide, hypothyroidism is most often the result of endemic iodine deficiency. In nonendemic areas, where iodine is sufficient in the diet, chronic autoimmune thyroiditis (Hashimoto s thyroiditis) accounts for the majority of cases. This disorder is primarily characterized by high levels of circulating antibodies against a key enzyme (thyroid peroxidase) in the processing of iodine in the thyroid gland. Blocking antibodies directed at the TSH receptor may also be present. Thyroid destruction may also occur via apoptotic cell death. 

Thyroid disorders may be divided into over- and underproduction of the thyroid hormones. These may be caused by thyroid gland disorders or disorders of the pituitary gland (TSH production) or hypothalamus (thyrotropin-releasing hormone release). Thyroid hormone deficiency in infancy may cause mental retardation if it is not corrected immediately after birth. For this reason, many states require thyroid function tests in all newborns. In adults, thyroid deficiency may be caused by Hashimoto s thyroiditis, an immune disorder, or dietary iodine deficiency, in which case it is called simple goiter. The term "myxedema" has been used to refer to hypothyroidism of whatever cause. Myxedemas may... 

Grave s disease (thyrotoxicosis) Hashimoto s thyroiditis Pernicious anaemia Addison s disease Diabetes Type 1 Goodpasture s syndrome Myasthenia gravis Multiple sclerosis ... 

Treatments for autoimmune disease have traditionally been immunosuppressive, antiinflammatory or palliative. Non-immunological therapies, such as hormone replacement in Hashimoto s thyroiditis, treat the outcomes of the autoaggressive response. Dietary manipulation limits the severity of coeliac disease. Steroidal or NSAID treatment limits the inflammatory symptoms of many diseases. 

With certain horse antitoxins and antiprotein sera and in some patients with Hashimoto s thyroiditis who have antibodies to thyro-globulin, one finds a different type of quantitative precipitation curve, termed a flocculation curve.Precipitation occurs only over a narrow range, and soluble antigen-antibody complexes are formed in the region of antibody excess as well as of antigen excess. Flocculation curves have... 

Treatment of thyroiditis (Hashimoto s thyroiditis, subacute thyroiditis of de Quervain). Where hyperthyroidism is a feature, treatment is by a P-adrenoceptor blocking drug. Antithyroid drugs should not be used. Where there is permanent hypothyroidism, the treatment is thyroid hormone replacement. 

Autoimmune diseases include autoimmune thrombocytopenia, Graves disease, hemolytic anemia, Hashimoto s thyroiditis, insulin-dependent diabetes mellitus (diabetes... 

Hypothyroidism is a relative deficiency in thyroid hormones. It manifests as a slowing down of all body functions or a decrease in metabolic rate. There are many causes for hypothyroidism, including Hashimoto s thyroiditis, drug-induced, radiation and radioactive iodine, dyshormono-genesis, congenital, and secondary causes (pituitary or... 

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