[TSH determination in central hypothyroidism]

Central hypothyroidism is one of the limitations of the use of sensitive TSH assays as first line screen in evaluating thyroid function. Studies on this subject are however scarce. The aim of the present study is to evaluate the usefulness of TSH assay before and after TRH on a large series of patients with central hypothyroidism. Fifty two patients presenting with post-partum hypopituitarism (Sheehan's Syndrome), 32 hypothyroids and 20 euthyroids were studied, as well as 21 normal females. There was no difference in TSH basal levels (TSH0) between the hypothyroid (1.43 +/- 0.98 mU/l), the euthyroid patients (1.45 +/- 0.83 mU/l) and the controls (1.32 +/- 0.58 mU/l). Delta TSH (TSH 30 mn after TRH-TSH0) was higher (p < 0.001) in the control group (8.48 +/- 3.76 mU/l) than in the euthyroid group (2.63 +/- 2.22 mU/l) that had a better (p < 0.001) response than the hypothyroid group (0.93 +/- 1.11 mU/l). Ten euthyroid patients had impaired response to TRH, while 6 hypothyroids had a normal test. This test has no advantage over basal TSH in central hypothyroidism diagnosis. TRH test gives many misleading results and have an elevated cost/benefit ratio as compared with the characteristic combination of low thyroxinemia and non elevated TSH0.