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.