Primary myxedema thyroiditis

AITD have high concentrations of circulating thyroid autoantibodies (Arai et ai, 2000 Carle et aL, 2006 Feldt-Rasmussen, 1996), for the most part the disorder appears to be the consequence of tissue damage initiated by T lymphocytes (Weetman and McGregor, 1994). Measurement of autoantibodies against thyroid peroxidase (TPO-Ab) and thyroglobulin (Tg-Ab) has for many years been a major tool in the diagnosis of autoimmune thyroid diseases, such as Hashimotos thyroiditis, primary myxedema and postpartum thyroiditis (Feldt-Rasmussen et ai, 1991 Feldt-Rasmussen, 1996). 

The TSH stimulation is primarily a test of thyroid reserve and has three main applications (1) to identify those patients with minor impairment in thyroid function where the conventional thyroid function tests produce normal results (2) to determine whether or not a patient, who is receiving thyroid therapy for presumed idiopathic myxedema, requires this therapy (3) to distinguish between idiopathic (primary) myxedema from hypothyroidism secondary to pituitary disease. 

Vallotton, M. B., Pretell, J. Y., and Forbes, A. P., Distinction between idiopathic primary myxedema and secondary pituitary hypothyroidism by the presence of circulating thyroid antibodies. J. Clin. Endocrinol. Metab. 27, 1-10 (1967). 

Hypothyroidism occurs in children (cretinism) and in adults (myxedema see Fig. 8-10). Myxedema may be primary and result from direct injury to the thyroid gland, or be secondary and due to interference with thyrotropin secretion. In contrast to primary myxedema, which is resistant to TSH injection, secondary myxedema can be corrected by thyrotropin administration. 

The pathogenesis of primary myxedema is not always easy to trace except when hypothyroidism follows thyroidectomy or massive necrosis of the thyroid. Autoimmune reactions probably are at least in some cases responsible for thyroid destruction. In myxedema, the thyroid is usually small and hard. Histologically, the typical follicular pattern has disappeared and is replaced by fibrosis. The thyroid is goitrous in a few cases, and presents the histological characteristics of hyperplasia. 

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