Endocrine Abstracts

Pituitary enlargement with long standing hypothyroidism is well established.

The clinical evolution of pituitary hyperplasia to thyroid hormone should be monitored closely during primary hypothyroidism because of the rare possibility of an incidental non thyrotropic pituitary tumor that will not regress on thyroid hormone. We report a case of a pituitary mass not responding to thyroid hormone therapy.

A 46 years old women was admitted for investigation for a pituitary adenoma. The patient presented for evaluation of amenorrhoea galactorrhoea and visual field changes.

Initial biochemical profile repeated twice was indicative of primary hypothyroidism with high levels of serum TSH: 100 mUI/ml (normal range (0.4–4 mUI/ml) with a FreeT4: 5 pmol/l (normal range: 12–24 pmol/l). Antithyroid peroxides (anti-TPO) were negative.

Prolactin level was 120 ng/ml. Dynamic tests of thyroid function included a TRH stimulation test which led to a strong stimulation of TSH to a peak at 300 mUI/ml.

A pituitary MRI revealed a symmetrical enlargement measuring 22 mm in height suggesting a pituitary hyperplasia. The patient was started on LT4 at a dose of 200 μg/day three months later (TSH: 1 mUI/ml while prolactin level remained high at 60 ng/ml two years later, the patient is euthyroid and still on amenorrhoea despite a normal TSH (0.13 mUI/ml). A pituitary MRI revealed a partial regression with persistence of mass of 19 mm suggesting a pituitary macro adenoma.

In conclusion: in patient with primary hypothyroidism complicated by pituitary hyperplasia, thyroid function tests and pituitary imaging may be unable to differentiate between pituitary tumor and hyperplasia.