Diagnosis of Equivocal Hypothyroidism, Using Thyrotropic Hormone (Tsh)*†

THYROTROPIC hormone (TSH) has proved to be a useful agent in differentiating primary thyroid myxedema from myxedema secondary to anterior pituitary insufficiency (1, 2, 3). In hypopituitarism the thyroid gland is dormant but responsive to stimulation, whereas in myxedema of thyroid origin there is no thyroid tissue to react. Using the uptake of radioactive iodine (I131) by the thyroid gland as a measure of its function, TSH substantially augments I131 uptake above baseline levels in pituitary myxedema and in normal individuals, but fails to induce any significant increase in thyroid myxedema. It seemed logical, therefore, to apply this technique to the study of subjects with equivocal, borderline or doubtful states of thyroid failure, in order to ascertain the presence of responsive thyroid tissue. Lack of responsiveness to TSH should be correlated with a diagnosis of hypothyroidism. The differential diagnosis between hypometabolism, asthenia, debility, senility and hypothyroidism may occasionally be extremely difficult. Thyroid failure is often suspected in nephrosis, disorders of menstruation, infertility, habitual abortion, neurasthenia, psychoses, and edematous states. Equivocal laboratory studies may further confuse the issue and any new technique that may serve as a diagnostic adjunct is worthy of trial. This study concerns the effect of TSH upon the I131 uptake of a group of patients suspected of hypothyroidism, to determine whether their response could be correlated with the final diagnosis.