Introduction: Prolactinoma and macroprolactin are important differentials in the diagnosis of hyperprolactinaemia. We present the case history of a patient with hyperprolactinaemia due to an unusual coincidence of macroprolactin and a non-enhancing pituitary lesion. Case history: A previously well female police officer aged 29, was referred to the endocrine clinic with a history of amenorrhoea and mastalgia for 3 years. She also complained of nausea, dizziness, weight gain, thin skin, mood swings, upper lip hair growth and scalp hair. Her initial biochemistry showed an elevated prolactin concentration of 2717 mIU/L with normal thyroid function tests and gonadotrophins. Iatrogenic causes for hyperprolactinaemia were excluded. A MRI scan showed appearances consistent with a microadenoma on the right side of the pituitary gland. Therapy with bromocriptine and then cabergoline was withheld due to severe nausea, dizziness and agitation. Due to ongoing problems with dizziness off Cabergoline/ Bromocriptine treatment, she had further tests including MRI of internal auditory meatus, pure tone audiogram and caloric tests at the balance clinic and they were normal. She was finally commenced on Quinagolide with no untoward side effects. Despite establishment of her menstrual cycles, the prolactin concentrations showed sustained elevation ranging from 2,5003,350 mIU/L instigating the search for macroprolactin. The recovery with PEG (polyethylene glycol) precipitation was 39% and gel filtration chromatography also identified the presence of macroprolactin contributing to 15% of the total prolactin concentration. Unfortunately, the further clinical course of our patient is unknown as she has been lost to follow-up.
Discussion: The occurrence of macroprolactin together with a prolactinoma has been documented before. Macroprolactin (minimally bioactive in-vivo) due to its variable cross-reactivity with prolactin immunoassay causes hyperprolactinaemia. Despite a demonstrable pituitary lesion, the possibility of contribution from macroprolactin needs to be considered in all hyperprolactinaemic patients with incongruent clinical history.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.