To compare the hypothyroid state in patients with thyroid cancer prepared either by placebo or L-T3 following L-T4 withdrawal in preparation for whole body scintigraphy. To evaluate the time needed for TSH elevation (> 30 mUI/L) on placebo vs. L-T3.

Patients with well differentiated thyroid cancer (DTC) need whole-body scintigraphy (WBS) and thyroglobulin (Tg) measurement in order to detect recurrence. Classically, withdrawal from levothyroxine (L-T4) during 4-6 weeks is needed for TSH elevation (> 30mUI/L), to allow iodine uptake and Tg production. As a result, patients become hypothyroid with impaired quality of life and a potential for tumour flare-up. Recombinant hTSH before WBS prevents hypothyroidism but is not yet approved for radioiodine treatment and is an expensive therapy. L-T3 substitution during the first 2-3 weeks of withdrawal is an alternative used empirically to prepare patients; however, no data exists to prove its benefit upon reducing hypothyroidism.

Objectives: 1) To compare the hypothyroid state in patients prepared either by placebo or L-T3 following L-T4 withdrawal. 2) To evaluate the time needed for TSH elevation (> 30 mUI/L) on placebo vs. L-T3.

Method: At the time of L-T4 withdrawal or after thyroidectomy, patients with DTC awaiting WBS or radioiodine treatment were randomized in two groups (double-blind): L-T3 (50 mg qd) or an identical placebo for 3 weeks, after which treatment was stopped for 2 weeks. A validated questionnaire of signs and symptoms of hypothyroidism (Billewicz's scale) was administered every 2 weeks until the WBS. TSH, fT4 and fT3 were measured weekly.

Inclusion Criteria:

• Patients with well-differentiated thyroid cancer, with total thyroidectomy
• 18 y.o. or older

Exclusion Criteria:

• Use of rhTSH for Whole Body Scintigraphy preparation
• Non stable cardiac arrythmias
• Any condition impairing TSH elevation(glucocorticoid use, hypopituitarism)
• Allergy to Liothyronine
• Inability to give a consent