Serum alpha-subunit elevation after TRH administration: a valuable test in presurgical diagnosis of gonadotropinoma?

Clinically nonfunctioning pituitary adenomas (CNFPAs) represent about 30% of pituitary macroadenomas, gonadotropinomas being the most frequent among them. The aim of the present study is to re-evaluate the usefulness of the measurement of alpha-SU serum level in response to TRH stimulation in detecting the gonadotropic nature of nonfunctioning pituitary adenomas before the neurosurgical treatment.

We have studied 14 patients with CNFPAs. The response of alpha-SU to the administration of TRH was studied in each patient before the surgery. alpha-SU blood serum level increase over 50% of the baseline level after TRH treatment was considered to be significant.

The patients were divided into 2 groups, each including 7 subjects. The first group included the patients with gonadotropinomas (tumors immunopositive for FSH and/or LH or their free subunits). The second group included the patients with adenomas immunonegative for gonadotropins and alpha-SU. The basal level of alpha-SU was elevated over the upper limit of normal range in two patients of the first group (gonadotroph adenomas) and in one in the second group. All but one patient from the first group and none of seven patients with tumors immunonegative for FSH, LH or alpha-SU, had a significant alpha-SU (over 50%) response to TRH. In three of seven patients with gonadotropins immunonegative tumors a decrease of alpha-SU serum level after TRH was observed.

The measurement of alpha-SU serum level in response to TRH administration seems to be useful in preoperative identification of gonadotroph adenomas among other nonfunctioning pituitary adenomas.