title: Immeasurably low and non-TRH-stimulatable TSH associated with normal I-123 uptake in two goitrous euthyroid patients: possible existence of other thyroid-hormone regulated thyroid stimulators other than TSH.
abstract: We described two euthyroid patients with normally functioning goiters, but with persistently undetectable and non-stimulatable TSH levels. Subject 1 was a 64-year-old woman with a large diffuse goiter who has been clinically and biochemically euthyroid without any medication for at least 19 years. Subject 2 was a 31-year-old woman with a small diffuse goiter who has been euthyroid for 4 years. Both patients had persistently undetectable levels of serum TSH, TSH receptor antibodies (TRAb) and thyroid stimulating antibodies (TSAb). Their basal TSH levels were very low and their T3 responses to TRH were very diminished or absent. In contrast, the basal levels of the other pituitary hormones and their responses to LHRH, GRH and CRH stimulation were all within normal limits in both patients. MRI images of pituitary glands, 123I thyroid uptake, and thyroid scans were normal. Ectopic thyroids were not detected on (99m)TcO4- and 123I total body scans. Factors interfering with the measurement of TSH were excluded by recovery studies. In subject 1 a T3-suppression test was positive and a perchlorate discharge test was negative. In subject 2 a T3-suppression test was negative. Euthyroid Graves' disease, subclinical hyperthyroidism, destructive thyroiditis, thyrotoxicosis of extrathyroid origin, central hypothyroidism, and nonthyroidal illness were all ruled out by these observations. These results suggest that an unknown factor, such as thyrostimulin, but not TSH or TSAb, stimulates the thyroid and maintains euthyroidism, and may have a role in the regulation of the hypothalamus-pituitary-thyroid axis.
authors.affiliation: Hyogo Health Service Association, Mikage-honmachi, Kobe, Japan.
authors.forename: Katsuji
authors.initials: K
authors.lastname: Ikekubo
authors.forename: Megumu
authors.initials: M
authors.lastname: Hino
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Saiki
authors.forename: Cheol
authors.initials: C
authors.lastname: Son
authors.forename: Toshio
authors.initials: T
authors.lastname: Iwakura
authors.forename: Hiromasa
authors.initials: H
authors.lastname: Kobayashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Ishihara
mesh_terms: D000328:Adult; D005260:Female; D006042:Goiter / Q000000981:diagnostic imaging / Q000378:metabolism / Q000503:physiopathology*; D006801:Humans; D018828:Immunoglobulins, Thyroid-Stimulating / Q000097:blood; D007455:Iodine / Q000493:pharmacokinetics*; D007457:Iodine Radioisotopes; D008875:Middle Aged; D011877:Radionuclide Imaging; D013961:Thyroid Gland / Q000000981:diagnostic imaging / Q000503:physiopathology*; D013963:Thyroid Hormones / Q000378:metabolism; D013972:Thyrotropin / Q000097:blood* / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014284:Triiodothyronine / Q000097:blood
chemical_list: D018828:Immunoglobulins, Thyroid-Stimulating; D007457:Iodine Radioisotopes; D013963:Thyroid Hormones; D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D007455:Iodine