Misinterpretation of prolactin levels leading to management errors in patients with sellar enlargement

Serum prolactin concentrations and clinical features were correlated with the histopathologic diagnosis in 128 patients, without acromegaly or Cushing's syndrome, referred for surgical treatment of a presumed pituitary adenoma. A serum prolactin concentration of more than 8,000 mU/liter was always due to a prolactin-secreting adenoma. Prolactin levels of less than 8,000 mU/liter occurred with a variety of pathologic diagnoses. Fifteen patients had lesions other than pituitary adenomas, most commonly intrasellar craniopharyngioma; 10 of these had modest hyperprolactinaemia (maximum, 5,260 mU/liter) and four had received inappropriate bromocriptine therapy. Adenomas that were not prolactinomas frequently caused mild hyperprolactinaemia, although this was usually less than 3,000 mU/liter; three of these patients, however, had serum prolactin concentrations greater than this (maximum, 8,000 mU/liter). If the serum prolactin concentration is less than 3,000 mU/liter in the presence of significant pituitary enlargement, surgical removal is essential for both diagnosis and treatment since only prolactin-secreting adenomas are likely to shrink with dopamine agonist therapy. A serum prolactin concentration between 3,000 and 8,000 mU/liter is consistent with any diagnosis, whether the fossa is greatly enlarged or not, and great care must be taken with dopamine agonist therapy in such patients.