Endocrine Abstracts

Hyperthyroidism associated to hyperthyrotropinemia is a rare condition which can be due to two different causes: resistance to thyroid hormones and TSH secreting adenoma. The differential diagnosis is not easy.

We have observed 8 patients with hyperthyroidism associated to inappropriately elevated TSH. All patients had similar basal levels of thyroid hormones and 7 out of 8 had a multinodular goiter.

Four out of 8 patients showed lack of TSH response to TRH stimulation. In all these cases MRI showed a pituitary adenoma. Two of them also showed lack of GH suppressibility after oral glucose load, suggestive of mixed adenoma secreting GH and TSH. Three out of 4 patients underwent successfull transsphenoidal surgery while one patient, affected by a mixed adenoma, was successfully treated by octreotide.

In the other 4 patients, TSH response to TRH stimulation was present, but 1 of them showed a pituitary adenoma. The thyrotoxicosis persisted after adenomectomy despite the decrease of TSH levels. Thyroidectomy was performed with histological diagnosis of Graves’ disease.

Three out of 4 patients were diagnosed as resistance to thyroid hormones. Two of them underwent thyroidectomy because of goiter. A papillary carcinoma was diagnosed in 1. This patient, because of the impossibility of obtaining a proper TSH suppression, represents a unique model of thyroid cancer follow-up under TSH constantly elevated.

These cases demonstrate that differential diagnosis of hyperthyroidism associated to hyperthyrotropinemia is hard to be done. It is necessary to evaluate clinical features, laboratory data and imaging. An adequate response to TRH in presence of mild clinical features is suggestive of resistance to thyroid hormones, while in case of overt hyperthyroidism other etiologies should be excluded. MRI scan is essential for diagnosis of TSH secreting adenoma.