Pituitary Macroprolactinoma with Mildly Elevated Serum Prolactin: Hook Effect

A 45-year-old man was admitted in our department with complaints of severe headache for over 6 months period. He also suffered from several problems such as visual field defect, decreased energy and libido, body hair loss, cold intolerance, decreased appetite and dry skin. On physical examination, he was afebrile: BP (blood pressure): 110/70 mm/Hg, PR (pulse rate) :65 beat/min, BMI (body mass index): 24. He had no terminal hair on face or chest and subcutaneous adipose tissue mass had been decreased substantially. Laboratory tests revealed; Hb: 12 g/dL (N: 14–17 g/dL), Total testosterone: 1.2 ng/mL (N:–-10 ng/mL), Luteinizing hormone (LH):3.3MIU/mL (N:1–8 MIU/mL), Follicle Stimulating hormone (FSH):1.3 MIU/mL (N:1–7 MIU/mL), T4:3.4 micg/dL (N:4–12 micg/dL), TSH:0.6 MIU/mL (N:0.5–5 MIU/mL), Prolactin:100 ng/mL (2–24 ng/mL), serum cortisol:6 MIU/mL (N:4–21 MIU/mL), IGF1:162 ng/mL (50–245). Pituitary MRI showed macroadenoma (29*16*14 mm) in left side of sella turcica which bulged to suprasellar cistern with pressure effect on left optic nerve (Figure 1, 2). Visual field examination revealed mild temporal hemianopia. These findings are consistent with macroadenoma and mild prolactin elevation. We also observed a discrepancy between pituitary tumor size and prolactin level. The correct estimate of serum prolactin was obtained after serial dilutional measurement. Serum prolactin after dilution was 6470 ng/mL. With these findings pituitary macroadenoma was diagnosed and treatment with cabergoline (dopamine agonist) 0.5 mg/week was started. After one month follow-up he had no symptoms, visual field defect was improved and pituitary MRI showed significant shrinkage of tumor.