Alterations in thyroid hormone economy in patients with hydatidiform mole

Studies of several aspects of thyroid hormone economy have been conducted in 11 patients before and after removal of a molar pregnancy. Before evacuation of the mole, all patients demonstrated moderately to greatly elevated values for thyroidal (131)I uptake, absolute iodine uptake, and serum protein-bound-(131)I. Values for serum PBI and serum thyroxine (T(4)) concentration were consistently and often greatly increased, averaging more than twice those found in normal pregnancy and three times those in normal controls. On the other hand, the maximum binding capacity of the T(4)-binding globulin (TBG) was variably affected, and ranged between the values found in normal controls and those found in normal pregnancy. Values for the absolute concentration of free T(4) in serum were, on the average, only moderately elevated, since the proportion of free T(4) was moderately low, although not as low as in normal pregnancy. Sera of patients with molar pregnancy contained high levels of thyroid stimulating activity, as assessed in the McKenzie mouse bioassay system. The stimulator displayed a more prolonged duration of action than that of TSH and did not reveal a major immunological cross-reactivity with either human or bovine TSH, differing in the latter respect from the chorionic thyrotropin of normal human placenta. Abnormalities in iodine metabolism were rapidly ameliorated after removal of the molar pregnancy, and this was associated with the disappearance from serum of the thyroid stimulator. Despite the foregoing evidence of thyroid hyperfunction and hypersecretion of T(4), patients with molar pregnancy were neither goitrous nor overtly thyrotoxic. They did display, however, high values of the urinary pigment/creatinine ratio, a possible indication of the presence of a hypermetabolic state. It is concluded that in patients with molar pregnancy, thyroid function and T(4) secretion are stimulated, often greatly so, by an unusual thyroid stimulator which is demonstrable in the blood and which is probably of molar origin. The nature of the stimulator, as well as the reasons for both the variability of the increase in TBG which occurs in molar pregnancy and the lack of frank thyrotoxicosis, remain to be clarified.