FRI314 Prolactinoma And Macroprolactin; A Diagnostic Dilemma

Disclosure: A. Farooqi: None. S. Dewan: None. J. Jun: None. Prolactin is a 199 amino acid, 23 (Kilo Dalton) kDa protein secreted by pituitary lactotroph cells. The two other major forms of prolactin present in circulation are big prolactin, the dimeric 40-60 kDa prolactin and big-big prolactin or macroprolactin, 100-150 kDa complexes of 23 kDa prolactin and IgG autoantibodies. Hypothalamic dopamine is the primary regulator of prolactin secretion through its inhibitory effect. Prolactinoma accounts for ∼40% of pituitary tumors with clinical presentations of hypogonadotropic hypogonadism and tumor-related mass effects. A 77-year-old female with a past medical history of hypertension and hyperlipidemia was admitted after a mechanical fall. She underwent a computed tomography (CT) of the brain which incidentally showed a pituitary mass. Magnetic resonance imaging (MRI) of pituitary showed a homogenously enhanced 3.0 x 3.5 x 2.8 cm mass centered in the Sella turcica, invading the supra-seller cistern, left cavernous sinus, and orbital apex abutting the optic chiasm and optic tracts. The patient did not report headache, nausea, vomiting, visual changes, or abnormal milky nipple discharge. Physical examination was unremarkable without any neurologic deficit. Formal ophthalmology evaluation showed intact extra ocular movements, visual field-testing using octopus 24-2 and Humphrey test showed few missed points, though not suggestive of pituitary related loss. Serum prolactin was measured at 1432 ng/ml (reference range, 0-25). The presence of macroprolactin was considered due to the absence of clinical features of hyperprolactinemia. The monomeric prolactin was found to be 68.7% (<40%) at 867.5 ng/ml of the total prolactin at 1259.7 ng/ml with 31.3 % of other prolactin forms are present. Evaluation for other pituitary functions was unremarkable with thyroid stimulating hormone (TSH) of 0.72 uIU/ml (0.49-4.76l), morning serum cortisol of 52.9 ug/dl (6.7-22.4), and insulin like growth factor (IGF-1) 73 ng/ml (20-214). Cabergoline 0.5 mg twice weekly was prescribed. This case illustrates a menopausal state as a probable explanation for lack of clinical features of hyperprolactinemia with macro adenoma while macroprolactin should be considered. Presentation: Friday, June 16, 2023