THE CLINICAL SIGNIFICANCE OF PLASMA THYROID‐STIMULATING ACTIVITY IN HYPERTHYROIDISM

Abstract

SUMMARYThe long‐acting thyroid stimulator (LATS) measured by the method of McKenzie was detected in 36 of 60 cases of untreated hyperthyroidism—a figure comparable with that in other reported series.An association was found between LATS and several clinical features. There was a definite correlation between LATS and the occurrence of exophthalmos. The mean LATS level of 433% in 13 exophthalmic patients was significantly greater than the mean of 230% in 50 patients without exophthalmos (P<0·02. There was also a significantly higher level of LATS (P<0·05) in 34 patients who had a visible goitre (323%) than in 24 without visible goitre (184%). Sixteen patients who eventually had a recurrence of hyperthyroidism after therapy were found to have a significantly higher mean LATS level (411%) than 34 subjects who remained well (182%) (P<0·01).No correlation could be found between plasma LATS level and (a) thyroid 131I turnover, (b) the plasma level of protein‐bound iodine and (c) the presence of a significant titre of antibodies to thyroglobulin in the patient's blood (Tanned red‐cell titre 1/2500).The association between LATS and pretibial myxœdema was demonstrated by two patients who both had elevated plasma levels of LATS and unequivocal pretibial myxœdema when first examined. Follow‐up studies over the ensuing three years demonstrated resolution of the pretibial myxœdema concurrently with disappearance of LATS from the plasma of one patient, and increasingly severe pretibial myxœdema associated with an increasing plasma level of LATS in the other.It is concluded that there is a significant relation between the plasma LATS level and various clinical features of hyperthyroidism. These data indicate the importance of LATS in relation to the pathogenesis of the disease. Recent chemical studies indicate that LATS belongs to the 7S globulins. These findings indicate that thyrotoxicosis, exophthalmos and pretibial myxœdema may result from disordered immunological mechanisms.