Distinction between idiopathic primary myxedema and secondary pituitary hypothyroidism by the presence of circulating thyroid antibodies.

Abstract

Immunologic studies for the detection of circulating antibodies, including the tanned red cell agglutination test, the complement fixation reaction and the double-layer technique of immunofluorescence, were compared in idiopathic primary myxedema (29 cases) and in secondary pituitary hypothyroidism of various causes (41 cases). The immunofluorescence technique was also applied for the detection of antibodies directed against the gastric parietal cells. Thyroid antibodies were detected at a significant level in idiopathic primary myxedema in 55% of cases by the TRC, and in 51.7 and 65.5%, respectively, for the cytoplasmic and the colloidal antigens by the immunofluorescence method, in contrast to 0 % by the TRC and 4.9 and 9.8% for the cytoplasmic and the colloidal antigens in secondary pituitary hypothyroidism. The complement fixation test was positive in only 10 cases, all primary myxedema. Antibodies to stomach were found frankly positive in 45 % of cases of primary myxedema and in 2.4% of cases of secondary hypothyroidism. The difference was still significant if the women of both groups were compared. The theoretical implications of these results are discussed with respect to the unsettled question whether antibodies precede, accompany, or are the consequence of anatomical alteration of the thyroid gland. The usefulness of these immunologic tests in differentiating primary involvement of the thyroid from secondary hypothyroidism is pointed out.