title: Thyroxine to triiodothyronine hyperconversion thyrotoxicosis in patients with large metastases of follicular thyroid carcinoma.
abstract: OBJECTIVE
  We experienced two cases of follicular thyroid carcinoma with distant metastases, which showed high levels of free triiodothyronine (T(3)) while free thyroxine (T(4)) levels remained in the low or normal range. In this report, we described the detail of these cases and examined the cause of T(3) thyrotoxicosis.
  
  
  METHODS
  In one of the cases, quantitative measurement of types I and II iodothyronine deiodinase mRNAs was performed using a surgically dissected tissue from the primary tumor and a distant metastasis.
  
  
  RESULTS
  In the both tissues, types I and II iodothyronine deiodinase mRNAs were expressed in the same level as in the normal thyroid tissues.
  
  
  CONCLUSIONS
  These results suggest that T(3) thyrotoxicosis in our patients was caused by hyperconversion of administered levothyroxine to T(3). In the follow-up of patients with distant metastases of follicular carcinoma, not only free T(4), but also free T(3) should be tested to avoid the excessive administration of levothyroxine.
authors.affiliation: Department of Laboratory Medicine, Osaka University Graduate School of Medicine, Suita, Osaka, Japan. ttakano@labo.med.osaka-u.ac.jp
authors.forename: Toru
authors.initials: T
authors.lastname: Takano
authors.forename: Akira
authors.initials: A
authors.lastname: Miyauchi
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Ito
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Amino
mesh_terms: D018263:Adenocarcinoma, Follicular / Q000097:blood / Q000473:pathology*; D000328:Adult; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis; D012333:RNA, Messenger / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000097:blood / Q000473:pathology*; D013971:Thyrotoxicosis / Q000150:complications* / Q000175:diagnosis; D013974:Thyroxine / Q000097:blood / Q000378:metabolism*; D014057:Tomography, X-Ray Computed; D014284:Triiodothyronine / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D014284:Triiodothyronine; D013974:Thyroxine