Hyperthyroidism and acromegaly caused by a pituitary TSH- and GH-secreting tumour

A female patient with acromegaly, TSH-induced hyperthyroidism and a large eosinophilic pituitary adenoma is reported. Granules in the adenoma cells were by immunohistochemical methods shown to contain GH and with monoclonal TSH-antibodies it was shown that 5-10 per cent of the cells secreted TSH. The basal serum TSH was elevated in the hyperthyroid phases and was not suppressible by exogenous T3 but decreased markedly with dexamethasone. There was a small subnormal rise in serum TSH after TRH injection which was totally suppressed by T3 (but not dexamethasone). L-dopa, bromocriptine and somatostatin caused a 20-30 per cent decrease in serum TSH. The alpha-subunit concentration was also elevated and was equally depressed by bromocriptine and somatostatin. The urinary excretion of TRH was within reference limits. This mixed tumour obviously secreted an excess of both GH and TSH causing acromegaly and hyperthyroidism.