Adequate thyroid-stimulating hormone levels after levothyroxine discontinuation in the follow-up of patients with well-differentiated thyroid carcinoma.
BACKGROUND
In the follow-up of patients with well-differentiated thyroid carcinomas (WTC), a thyroid-stimulating hormone (TSH) >or=30 micro U/mL is generally accepted as adequate to perform whole body scans (WBS), determine thyroglobulin (Tg), and administer radioiodine therapeutically. These patients, inevitably rendered hypothyroid, are traditionally switched to T3 for 3-4 weeks prior to withdrawing all thyroid hormones for an additional 2-3 weeks. Neither TSH and Tg elevation dynamics nor WBS characteristics after simply interrupting L-T4 treatment without T3 administration have been evaluated.


METHODS
TSH, total T4 and T3, as well as FT4 were measured weekly after discontinuing L-T4 in 21 subjects (group I) and after thyroidectomy in 10 subjects (group II). WBS and Tg determination was performed upon achievement of TSH >or=30 micro U/mL.


RESULTS
By the second week, 42% of group I patients and 70% of group II patients had TSH >or=30 micro U/mL. By the third week, 90% in group I and 100% in group II had achieved this target. Group I patients who needed 4 weeks to increase TSH received a greater cumulative radioiodine dose and had higher Tg levels. Positive WBS were found in eight cases and the incidence of a negative WBS with elevated Tg was significantly higher when evaluation occurred at the second week of L-T4 withdrawal compared to the fourth week.


CONCLUSIONS
L-T4 interruption is a reasonable alternative to temporary T3 in preparation for radioiodine scanning and treatment.
Sánchez
Reyna
R
Servicio de Endocrinología, Unidad de Investigación Médica en Endocrinología Experimental, Hospital de Especialidades, Centro Médico Nacional Siglo XXI (CMN-SXXI), Instituto Mexicano del Seguro Social (IMSS), Mexico City, Mexico.
Espinosa-de-los-Monteros
Ana Laura
AL
Mendoza
Victoria
V
Brea
Eduardo
E
Hernández
Irma
I
Sosa
Ernesto
E
Mercado
Moisés
M
D000328:Adult; D002454:Cell Differentiation; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011877:Radionuclide Imaging; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy* / Q000473:pathology; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood / Q000494:pharmacology*; D013997:Time Factors; D014284:Triiodothyronine / Q000097:blood
D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine