Endocrinological evaluation of ACTH-secreting pituitary microadenomas: their location and α-melanocyte stimulating hormone immunoreactivity

It has been hypothesized by Lamberts and coworkers in their analysis of 15 cases that adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas may be derived from either the anterior lobe or the intermediate lobe. The intermediate lobe type of Cushing's disease is thought to be controlled through a hypothalamic pathway and is characterized by hyperprolactinemia, suppressibility of cortisol with bromocriptine, and lower sensitivity to dexamethasone. The authors investigated the validity of this hypothesis in 125 cases of ACTH-secreting pituitary microadenomas by analyzing the endocrine findings, the locations of the microadenomas, and alpha-melanocyte stimulating hormone (alpha-MSH) immunoreactivity in the adenoma cells. No significant differences in the basal hormone levels, cortisol suppressibility with bromocriptine, sensitivity to dexamethasone, and recurrence rate were observed between patients with the microadenoma adjacent to the posterior lobe (considered typical of the intermediate lobe-derived tumor) or those with the microadenoma located in the anterior lobe. The locations of the microadenoma were not correlated with alpha-MSH immunoreactivity in the adenoma cells. No significant differences in endocrine findings were noticed between adenomas positive or negative for alpha-MSH. Thus, Cushing's disease cannot be simply divided into either the anterior lobe type or the intermediate lobe type by endocrinological evaluation as described by Lamberts, et al.