Endocrine Abstracts

Prolactinomas are the most common hormone-secreting pituitary tumors. They typically present with hypogonadism, decreased libido, infertility, and gynaecomastia in men. We present an interesting case of a 44-year-old gentleman who was referred to our endocrine clinic for ‘abnormal thyroid function tests’ with a low T4 despite a normal TSH (TSH 2.01, T4 7.5, T3 3.9). He reported a few years’ history of increasing weight gain and lethargy, generalized aches and pains, occasional frontal headaches and low libido. His visual fields were normal to confrontation. There were no clinical features suggestive of cortisol excess. TFTs suggestive of central hypothyroidism (CH) led to a full pituitary profile as follows: Prolactin 131,000, Macroprolactin negative. Oestradiol <100, LH 0.5, FSH 1.4, testosterone 1.1, SHBG 11, GH<0.05, IGF1 12.3, random cortisol 278. MRI pituitary confirmed a large macroadenoma with expansion into the left cavernous sinus and suprasellar extension causing displacement of the optic chiasm. A diagnosis of pituitary macroprolactinoma was made with evidence of secondary hypothyroidism and hypogonadism. He was started on Cabergoline 250 mcg weekly uptitrated to 500 mcg 3× week over a period of few months with reduction in prolactin levels from 131000 o 12566 (see attached graph 2). Insulin tolerance test to further assess his anterior pituitary function revealed a baseline cortisol of 225 with peak cortisol 284, baseline GH <0.05 with peak GH 0.06 consistent with secondary cortisol and GH deficiency. He was started on Hydrocortisone 10 mg, 5 mg, and 2.5 mg. Levothyroxine was started few weeks after this. A repeat MRI 3 months since start of treatment showed reduction in size of lesion particularly the suprasellar and left parasellar components with no displacement of the optic chiasm.

Learning points:

- Treatment with dopamine agonists is usually well tolerated and effective in normalizing the prolactin level and shrinking the tumor mass of even large prolactin-secreting tumors.

- We wish to highlight the importance of identifying the spectrum of ‘abnormal’ thyroid function and having a high suspicion to consider a pituitary pathology with a picture suspicious of central hypothyroidism. Our case had a mildly low free T4, with normal TSH that led to a diagnosis of a macroprolactinoma with anterior hypopituitarism.

- Patients with central hypothyroidism usually display mild to moderate non-specific symptoms and signs similar of primary hypothyroidism.

- In patients at risk for combined pituitary hormone deficiencies potential concomitant central adrenal insufficiency must be excluded before starting levothyroxine therapy due to the risk of precipitating an adrenal crisis.