Diurnal variation of prolactin secretion differentiates pituitary tumors from the primary empty sella syndrome

In an attempt to find an endocrine function test that might be useful in differentiating the primary empty sella syndrome from a pituitary tumor, we evaluated 24-hour prolactin levels in seven patients with the primary empty sella syndrome, 16 patients with pituitary tumors and 37 normal subjects. All eight patients with the primary empty sella syndrome had normal 24-hour mean prolactin levels and normal diurnal variation of prolactin release whereas in each patient with a pituitary tumor nocturnal prolactin secretion was blunted. In light of these findings and those of other investigators, we do not perform routine invasive study of the pituitary in patients with (1) a typical clinical presentation of the empty sella syndrome, (2) no endocrinopathies, (3) a normal computerized axial tomography scan, when indicated, and (4) normal serum prolactin levels with intact diurnal variation.