Isolated idiopathic central hypothyroidism in an adult, possibly caused by thyrotropin releasing hormone (TRH) deficiency.

Central hypothyroidism (Central H) is mainly due to acquired lesions, either in the pituitary, the hypothalamus or both, and in such cases it is usually associated with deficient secretion of ther pituitary hormones. Isolated central hypothyroidism (I Central H) remains a very rare disease. By the use of the serum thyroid stimulating hormone (TSH) assay as an initial screening test for thyroid disease, the diagnosis of I, Central H can be missed or delayed, since most of these patients have normal or even slightly high serum TSH concentrations. We present a 54-year-old woman with intense tiredness, in whom hypothyroidism was initially and persistently excluded because of normal TSH levels. Further investigations showed again a normal TSH with slightly low free thyroxine (FT4), and Central H was suspected. A thyrotropin releasing hormone (TRH) stimulation test confirmed the diagnosis. No lesion was found by magnetic resonance imaging (MRI). No other pituitary hormone insufficiency was detected. Finally, after excluding, the intake of any drug affecting the hypothalamo-pituitary-thyroid axis and the presence of critical systemic illness, the unusual diagnosis of idiopathic isolated Central H was made. When suspecting Central H, both FT4 and TSH should be measured and if these values are low, TSH response to TRH is recommended to reach specific diagnosis.