Serum long acting thyroid stimulator (LATS) and LATS-protector (LATS-P) in Graves' disease associated with localized myxedema.

When localized myxedema occurs in Graves' disease, there is often very high serum long acting thyroid stimulator (LATS) activity. However, this association is not invariable and no pathogenetic role for this IgG associated activity is known. Serum LATS protector (LATS-P) is a closely related IgG activity which is present in the majority of cases of untreated Graves' disease. It usually coexists in LATS positive sera in a substantially greater concentration. Its association with localized myxedema has not been studied, nor have serial studies been performed on this activity during the clinical course of the disease. Fourteen patients (13 females, 1 male) with localized myxedema and a history of Graves' disease were examined. In 13 serum LATS was detectable with a wide range of activity from 2.4 to 1,000 units/ml. Serum LATS-P was detected in all including the LATS negative patient with a range of activity from 46 to 4,068 units/ml. Serial studies for at least 2 years were conducted in 8 patients. In two there was no change in either skin lesions or in serum LATS and LATS-P. In 6 the skin lesions partially or completely resolved. In 5 this was associated with statistically significant falls in serum LATS and LATS-P but in one no significant change occurred. The study demonstrated the high prevalence of LATS and LATS-P in localized myxedema. In the sole LATS negative patient there was a high concentration of LATS-P. The role of these activities in the pathogenesis of the disease remains unknown but in serial studies falls in activity were usually associated with clinical improvement.