Macroprolactinomas masquerading as pseudoprolactinomas: the high dose hook effect

ABSTRACT

Serum prolactin level is very important to discriminate prolactiomas from other causes of hyperprolactinemia, specially pseudoprolactinomas. We describe two hyperprolactinemic men case 1 is 28y old with headache, left eye visual loss and ptosis associated with a huge mass of the sellar region who was operated on elsewhere by transcranial route. These was no visual amelioration. Two months after surgery the patient was admitted to our Unit with impairment of right eye vision. Galactorrhea was found and imaging evaluation showed persistence of a large tumor. After blood sampling for hormonal assessment, oral bromocriptine (10 mg/day) was started and a dramatic right visual improvement was noticed. However, basal prolactin by immunoradiometric assay (IRMA) was 97mug/L. Due to the clinical signs and response suggesting prolactinoma, prolactin level was reassessed. A two-incubation and serial dilution of the same sample up to 11,200 disclosed a prolactin value of 25,572 mug/L. Case 2 is 20y old with headache, bitemporal hemianopsia, seizures and hypogonadism secondary to a giant tumor arising from the sellas region. Initial serum prolactin level measured by IRMA was 104 mug/L, which after two-incubations and dilutions up to 1200 disclosed a value of 17,736 mug/L; clinical treatment was instituted with good results. In order to avoid unnecessary surgeries, we recommend a two-incubation procedure in routine prolactin determinations when IRMA is used.