Large somatostatin-insensitive thyrotrophin-secreting pituitary tumour responsive to d-thyroxine and dopamine agonists

Abstract

A unique thyrotrophin (TSH)-secreting pituitary tumour is described in a patient with a history of recurrent thyrotoxicosis. Unlike other previously reported TSHomas, the tumour is insensitive to octreotide, a somatostatin analogue. It does not accumulate [111In]octreotide but expresses functional dopamine receptors and responds to the d-isomer of thyroxine, two characteristics beneficial in the management of the patient.Patients with TSH-secreting pituitary tumours are rare.

Neuroendocrine Tumor Markers

“…Probably, corticotroph adenomas do produce CgA, but as these microadenomas frequently have a diameter of only a few millimeters, their small CgA production may not be enough to raise the concentrations in the petrosal venous circulation. CgA is produced by a wide variety of normal neuroendocrine tissues throughout the body [11]. Its circulating plasma pool is substantially greater than that of many other peptide hormones and it has a relatively long plasma halflife of 16-18 minutes [26].…”

“…Although its biological role has not yet been established, its potential value as a marker of endocrine function is apparent. One of the most promising clinical uses is its ability to identify non functioning endocrine tumours [10][11][12]. Most hormone-negative neoplasms of endocrine origin retain the capacity to produce egA.…”

“…It is a velY hydrophilic protein with an abundance of charged, mostly acidic amino-acids. It contains multiple sites with two or more adjacent basic amino-acids, far exceeding the number observed in other proteins [10][11][12]. Seven of these dibasic residues are conserved in all mammalian CgA species.…”

“…Therefore several investigators have tried dopamine agonist therapy, usually bromocriptine, in patients with CNPA. The results are rather disappointing, however, showing improvement of visual field defects and/or reduction of tumour mass in only a small number of patients [11,[20][21][22][23][24]. Since bromocriptine is generally not well tolerated in high doses, rather low doses were used in these studies.…”

In vivo imaging of pituitary tumours using a radiolabelled dopamine D2 receptor radioligand

“…Variable effects of dopamine agonists in TSH-secreting tumours have been reported, and suppression of the inappropriate TSH secretion by these agents has been demonstrated in a few cases (Karlsson et al, 1993;Verhoeff et al, 1993).…”