Background: Prolactin (PRL) secreting pituitary tumours are the most frequent causes of hyperprolactinaemia in clinical practice.
Case: A 78-year old man presented with gradual visual deterioration over two years particularly affecting left eye and getting progressively worse. Formal visual field testing suggested grossly constricted field defect in left eye and superior temporal field defect in right eye. Examination showed no features of acromegaly. Static pituitary profile including IGF-1 was normal. PRL level (reference range: 0360 mu/l) was markedly raised at 41,042 mu/l (negative macroprolactin screen). Magnetic Resonance Imaging (MRI) of brain confirmed a pituitary macroadenoma extending superiorly to the left side displacing the optic chiasm and the adjacent frontal lobe upwards, with tumour extension into the left cavernous sinus displacing the superior part of the left carotid loop supra-laterally. Surgical treatment was not deemed appropriate at that stage. He was commenced on cabergoline at a dose of 250 mcg twice a week. When reviewed six days later with repeat PRL levels, the patient had already noticed a slight improvement in his vision, even at that stage. PRL levels had reduced significantly to 1735 mu/l after two tablets of 250 mcg cabergoline. After three weeks of treatment, his PRL levels was near normal at 371 mu/l. Repeat MRI scan at two months demonstrated 40% decrease in the volume of the pituitary macroadenoma with marked reduction in the compression of the left side of the optic chiasm. Ophthalmology review confirmed considerable improvement in his visual fields.
Comment: In our patient, the PRL levels decreased to near normal within a period of 3 weeks and the tumour size shrunk by 40% within 8-weeks in contrast to previous reports where tumour shrinkage took 312 months and PRL levels normalised only after 4-months. Such rapid improvement is uniquely distinct in comparison to available literature reports.