Limitations of using serum prolactin as a guide to distinguish between a prolactinoma and a non-functioning pituitary adenoma with disconnection hyperprolactinaemia.
Amin A1, Mendoza N2, Mehta A3, Meeran K1, Hatfield E1, Martin NM1
1Department of Endocrinology; 2 Department of Neurosurgery; 3Department of Radiology. Charing Cross Hospital, Imperial College Healthcare NHS Trust, Fulham Palace Road, London W6 8RF
A 28 year old man presented in June 2009 to the Neurologists with a 3 month history of headaches and visual loss. He was shaving twice weekly and had a recent absence of morning erections. Perimetry confirmed a well demarcated bitemporal hemianopia. A MRI of his pituitary gland revealed a large pituitary macroadenoma with elevation and compression of the optic chiasm and involvement of the left cavernous sinus. He was transferred to our centre for urgent surgical intervention. Endocrine review confirmed an elevated prolactin 10,175 mU/L (negative for macroprolactin), low random cortisol 62 nmol/L, probable growth hormone deficiency GH <0.05 mg/l, IGF-1 9.0 nmol/L (NR 15-37 nmol/l), secondary hypothyroidism TSH 2.27 mU/L, fT4 6.6 pmol/L, and secondary hypogonadism LH <0.05 IU/L, FSH 1.6 IU/L, testosterone 0.5 nmol/L.
The endocrine team was concerned that the prolactin level was higher than expected for a non-functioning pituitary adenoma and requested that surgery by postponed. Serial dilutions were performed which confirmed the prolactin result remained elevated at 11,000 mU/L. He was commenced on hydrocortisone and cabergoline 250 mcg twice weekly. The aim was to assess whether there was an improvement in his visual fields in the short-term, to support the use of medical rather than surgical treatment in this patient. However, there was little change of his visual fields following three weeks of treatment, and hence he was referred for urgent transsphenoidal surgery. There was good improvement of his visual fields post-operatively. Histology confirmed a bony invasive gonadotroph adenoma secreting FSH beta subunit, supporting a diagnosis of a non-functioning pituitary adenoma with disconnection hyperprolactinaemia rather than a prolactinoma.
This case highlights a number of important points. Prolactin cannot always be used reliably to guide whether a large pituitary tumour, in the context of hyperprolactinaemia, is a non-functioning pituitary adenoma or a prolactinoma. This case shows the limitations of a proposal to use a cut-off for serum prolactin of >2000 mU/L to distinguish between these two tumour types.