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Atrophic autoimmune thyroiditis (primary myxedema) is, after postablative hypothyroidism, the most common cause of thyroid failure in the adult. It is more common in women than in men and usually occurs between the ages of 40 and 60 atrophic autoimmune thyroiditis, autoimune. The presence of circulating thyroid autoantibodies in as many as 80% of the patients and overlap of the clinical and immunologic features with the autoimmune diseases indicate that what was once thought to be a separate disease in fact represents the end stage of an autoimmune thyroiditis in which goiter either was absent or had gone unnoticed prior to atrophy. Although most cases probably reflect autoimmune destruction of the thyroid parenchyma, some cases of nongoitrous hypothyroidism are due to antibodies that block the response to endogenous TSH, so-called blocking TSHR autoantibodies. Primary hypothyroidism may also occur as part of an autoimmune syndrome of polyglandular failure.
On histopathologic examination the thyroid remnant consists largely of fibrous tissue with an occasional thyroid follicle and foci of lymphocytic infiltration. The thyroid is usually impalpable or normal in size. Typical laboratory findings.
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