Hyperthyroidism due to non-tumoural inappropriate TSH secretion

Abstract
Inappropriate hypersecretion of TSH was investigated in a 25 year old man whose hyperthyroidism had relapsed 4 years after subtotal thyroidectomy. Serum TSH levels were further increased by both TRH and metoclopramide and were partially suppressed by triiodothyronine (120 μ/day). The serum α-subunit: TSH molar ratio was < 1.0, and computerised axial tomography showed no evidence of a pituitary tumour. These features are characteristic of inappropriate TSH secretion due to thyrotroph resistance to thyroid hormones. A long-acting somatostatin analogue (SMS 201-995), 50 μg injected sc twice-daily for three days, suppressed TSH levels and nearly normalised thyroid hormone levels. Somatostatin analogues may be therapeutically useful in thyrotoxicosis due to non-tumoural inappropriate TSH hypersecretion.

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