Unresponsiveness to exogenous TSH in obesity.

(1). Assessment of thyroidal and other indices in 275 instances of obesity with body weight excesses up to 200 percent or more of the ideal revealed absent thyroidal I131 uptake responses to TSH in about one out of five patients. Moreover, basal thyroidal I131 uptake of 10 percent or less, prolongation of ankle reflex time, or high levels of serum cholesterol were present in a minority. Also, occasional instances of unduly elevated serum TSH titers were found. Some of the indices deviated from normal more often with the greater excesses of body weight or with increased age. (2). These findings are consonant with a hypothesis that routine thyroidal or related indices are sporadically abnormal in massive obesity almost always without overt hypothyroidism or myxedema, that total unresponsiveness to exogenous TSH is surprisingly frequent, and that such unresponsiveness represents an unexplained endocrine anomaly in association with gross overweight. (3). Our data suggest that some obese persons are not able to respond to exogenous TSH, nor, presumably, to increases of endogenous TSH. This could result in an economy of caloric expenditure and play a contributory role in the genesis or the perpetuation of the obesity.