s at least secreting prolactin (a prolactinoma), but these things tend to secrete more than one
hormone--what are his ACTH, TSH, GH, FSH, LH, and ADH levels? These are all hormones secreted by the pituitary, and I imagine he's had these levels monitored at one time or another.
I really think that pituitary tumor is causing a lot of these problems...ADH is secreted by the anterior lobe of the pituitary and improper secretion of this results in diabetes.