[Gonadotroph Pituitary Adenoma Causing Severe Headache Following Repeated Use of GnRH Agonist for Prostate Cancer].

Gonadotropin-releasing hormone (GnRH) agonists play an important role in androgen deprivation therapy (ADT) employed for locally advanced prostate cancer. A 76-year-old man presented with elevated levels of prostate-specific antigen (PSA, 8.33 ng/ml). Subsequently he was diagnosed with cT3bN0M0 prostate cancer, Gleason score 4＋5. Before he was referred to our clinic, he had been administered bicalutamide (80 mg/day) daily by the referring physician, followed by subcutaneous injection of goserelin (3. 6 mg) 15 days later. The second dose of another GnRH agonist (leuprolide, 22.5 mg) was administered at his first visit to our clinic, 11 days after goserelin injection, at the discretion of the attending physician (26th day after bicalutamide administration). Bicalutamide administration was concomitantly maintained throughout the period. The patient presented with severe headache the next morning, and imaging studies detected a prominent pituitary adenoma. A trans-sphenoidal surgery was conducted for symptomatic relief. Histopathological analysis revealed a gonadotroph (follicle-stimulating hormone-secreting) pituitary adenoma. Although speculative, repeated injection of GnRH agonist was concluded to be the most likely cause of acute symptomatic gonadotroph pituitary adenoma. The irregular use of medication can cause undesirable and unanticipated adverse events. Awareness is the key to the prevention of such conditions.