A nineteen year old man was admitted by his GP with profound weight loss. He had avoided contact with primary care services as he feared doctors, but had been referred to an eating disorders clinic. He had a diet of exclusively snack food and had been losing weight for two years.
On examination he was cachectic and pale with scanty body hair. His body mass index was 13 kg/m2, with a weight of 44 kg. He was clinically thyrotoxic, a small diffuse goitre was palpable and bitemporal hemianopia was detected.
Admission tests revealed TSH 24 miu/L, freeT4 >100 pmol/L and alpha subunit 100.5 iu/L. He also had a microcytic anaemia, elevated GH and SHBG levels. Interestingly IGF-1 levels were low. Further tests were consistent with secondary hypoadrenalism and hypogonadotrophic hypogonadism.
MRI pituitary revealed a large pituitary adenoma with invasion of the cavernous sinus bilaterally, sphenoidal sinus and extension into the suprasellar cistern to the level of the third ventricle. There was associated hydrocephalus.
Corticosteroid and testosterone replacement were initiated, followed by treatment with octreotide. This has led to a doubling of his weight over 3 months, a small improvement in his visual fields, and significant shrinkage of the pituitary macroadenoma on serial MRI scans. GH, SHBG and TFTs have normalised. IGF-1 level has risen. The microcytic anaemia has resolved with oral iron supplementation and dietary changes.
TSH secreting adenomas are rare and account for less than one percent of all pituitary tumours. 14 percent of these co-secrete GH. This case highlights that thyroid function should be checked in all patients with unexplained weight loss. It also demonstrates the effectiveness of octreotide in tumour shrinkage and that IGF-1 levels may be misleadingly low in states of profound weight loss.