Endocrine Abstracts (2004) 7 P277

A diagnostic pitfall: concomitant occurrence of macroprolactinaemia and a non-secreting pituitary adenoma

U Krishnan1, MZ Qureshi1, J Burrows2, M Labib2 & TM Fiad1

1Department of Endocrinology, Dudley NHS Trust, West MIdlands, UK; 2Department of Clinical Biochemistry, Dudley NHS Trust, West MIdlands, UK.

We present the case of a 49 year old man who initially presented to his GP with complaints of tiredness, weight gain and tingling in his right hand. GP requested thyroid hormone measurements which showed FT4 level of 3.4 picomoles per litre and TSH 10.89 milli international units per litre. The inappropriately low TSH level raised the possibility of central hypothyroidism and triggered further investigations which revealed a low level for GH, LH, FSH, testosterone and cortisol and a prolactin value more than 5,400 milli units per litre. He was seen in our endocrine clinic on an urgent basis. He denied headaches, decreased libido, visual symptoms or galactorrhoea. Visual fields were normal by confrontation. Insulin induced hypoglycaemia test showed a peak cortisol of 203 nanomol per litre. Repeated prolactin measurement showed a value more than 14,800 milli units per litre. MRI scan of the pituitary showed a macroadenoma without pressure effects. A diagnosis of prolactin secreting macroadenoma with panhypopituitarism was made and he was commenced on cabergoline as well as hydrocortisone and thyroxine replacement. Subsequent screen for macroprolactin confirmed the presence of macroprolactin in the patient's serum interfering with prolactin assay. Gel precipitation quantified the macroprolactin level as significant. On clinic follow-up and while on cabergoline therapy, his repeat MRI showed increase in size of the pituitary adenoma, but still without local pressure effects. Patient's diagnosis was revised to non-secreting pituitary adenoma and concomitant presence of macroprolactinaemia. He was referred for neurosurgery. In summary, the rare co-existence of macroprolactin and a non-functioning pituitary adenoma represented a misleading situation which led to delay in making the correct diagnosis. This case highlights the importance of screening for macroprolactin in all subjects with hyperprolactinaemia even if there is evidence of pituitary dysfunction.

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