Differences in Pathological Findings and Growth Hormone Responses in Patients with Growth Hormone-Producing Pituitary Adenoma

Plasma growth hormone (GH) responses to various stimuli were examined in 21 patients with GH-producing pituitary adenomas, classified into three types by the immunohistochemistry of cytokeratin and the glycoprotein hormone α-subunit distribution. Seven type 1 adenomas were exclusively composed of cells in which the cytokeratin formed a dot-like pattern; they were chromophobic to hematoxylin and eosin (H & E), occasionally positive for GH, and almost completely negative for the α-subunit. Thirteen type 2 adenomas were composed of cells with cytokeratin that had a perinuclear distribution; they were eosinophilic to H & E, and diffusely positive for both GH and the α-subunit. One patient had a type 3 adenoma which had a mixed pattern of intracellular cytokeratin distribution and was chromophobic and eosinophilic to H & E. Clinically, type 1 is characterized by earlier onset, larger tumor size, and more frequent aggressive extension. Paradoxical GH responses to TRH and OGTT were seen in 1 of 6 patients (16.7%) of type 1 and 8 of 9 patients (88.9%) of type 2, and 0% of type 1 and 62.5% of type 2, respectively. Type 2 cases showed higher plasma GH response to GH-releasing hormone, and a tendency to greater suppression of plasma GH by bromocriptine compared with type 1. Octreotide acetate administration revealed that the nadir/basal ratio of plasma GH levels was 42.9±6.6% in type 1 and 13.5±5.8% in type 2. These results suggest that there is a pathophysiological difference between these two distinct types of GH-producing pituitary adenomas.