Prolactinoma in a Male to Female Transgender Woman on Gender Affirming Hormone Therapy

Background: Estrogen promotes prolactin secretion and its role in prolactin secreting adenomas is still under investigation. The genesis and resolution of prolactinomas may be affected by gender affirming hormone therapy. Case Description: A 50 year old transgender female presented with new onset tunnel vision and extremity parathesias for one day. She had been taking oral estrogen for six years. Physical exam showed bilateral gynecomastia as well as galactorrhea. Her visual fields were intact by confrontation. Her brain MRI revealed a pituitary macroadenoma measuring 1.4cm x 1.3cm x 1.3cm. Laboratory studies showed prolactin 538 ng/mL (<20 ng/mL), IGF-1 89.0 (66-303 ng/ml). TSH 1.7 (0.4-4.7 mcIU/mL), Free T4 0.997 (0.58-1.76 ng/dL) and estradiol 103 pg/ml (N/A). She was treated with bromocriptine 5mg daily. Three months later galactorrhea had resolved, but gynecomastia was unchanged. The patient had a prolactin level of 3 ng/mL. Follow up brain MRI at one and three years showed no significant decrease in size of macroadenoma. Discussion: Despite this patient’s biochemical and symptomatic response to dopamine agonist therapy, her pituitary adenoma did not decrease in size over 3 years, which is a common occurrence with macroprolactinomas. However, her prolactin levels declined and her galactorrhea resolved with therapy. Research into the long term effects of gender transition therapy remains mainly in the realm of case reports and retrospective studies. Our review of the medical literature suggests that some transgender patients on estrogen therapy may have an increased risk of developing pituitary adenomas. However, guidelines have not yet been published and currently there are no recommendations for routine imaging or biochemical assessment during follow-up of these patients. While there are established reference ranges for prolactin levels for men, non-pregnant and pregnant women, no established reference ranges for prolactin levels are available for transgender women on gender affirming hormone therapy. Studies indicate that 76-86% of patients have a reduction in the size of their prolactinomas after dopamine agonist therapy. However, the same may not be true for transgender women on transfeminine hormone therapy with estrogen. Conclusion: Prolactinomas may commonly occur and be masked in transgender women on gender affirming hormone therapy due to the expected symptoms of gynecomastia, erectile dysfunction, and diminished libido from reduced testosterone levels. Estrogen promotes prolactin secretion by the pituitary gland and may have a role in development and expansion of prolactinomas. More research is needed in regards to the assessment and monitoring of the pituitary gland in transgender women on gender affirming hormone therapy with estrogen.