Method of Endogenous TSH Stimulation in the Follow-up of Differentiated Thyroid Cancer

The treatment of differentiated thyroid cancer (DCT) includes surgery followed by radioiodine treatment. In the follow-up of patients it is necessary to induce TSH elevation to test for cancer recurrence. One of the options is to stop L-thyroxin replacement for several weeks. Current pilot study aims to induce the necessary TSH elevation by decreasing the L-thyroxin dose. The main hypothesis is that necessary TSH stimulation will be achieved during 4-6 weeks in majority of patients.

The treatment of differentiated thyroid cancer (DCT) includes surgery followed by radioiodine treatment. In the follow-up of patients it is necessary to induce TSH elevation for the measurement of thyreoglobulin and/or total body scanning. There are two principal methods to obtain TSH elevation: 1) injection of recombinant human TSH , and 2) to stop L-thyroxin replacement for several (3-4) weeks. As use of recombinant TSH is rather expensive, this method is not feasible in many countries. The problem with stopping L-thyroxin is development of severe hypothyroidism for several weeks with concomitant symptoms and signs. Current pilot study aims to induce the necessary TSH elevation by decreasing the L-thyroxin dose. The main hypothesis is that necessary TSH stimulation will be achieved during 4-6 weeks in majority of patients with fixed dose of L-thyroxin. Concomitantly, blood tests and symptoms and signs of hypothyroidism will be obtained to get information about possible deviations during treatment with low dose of thyroxin.

Low dose of L-thyroxin (50 microg/day) will be used during 4 weeks. If TSH is < 30 after 4 weeks the study continues up to 6 weeks.

The percentage of patients obtaining TSH level at least 30 imU/L at the end of study period. Blood tests will be obtained after 4 weeks. If TSH > 30 the patient has completed the study. If TSH < 30 patient will continue for 1 week and blood tests will be obtained after week 5. If TSH > 30 the patient has completed the study. If TSH < 30 patient will be monitored during 1 week and blood tests will be obtained after 6 weeks.

Billewitz index measures the severity of hypothyroidism symptoms. Billewitz index will be recorded after 4 weeks and after 5 and 6 weeks if patient continues after 4 or 5 weeks (see primary endpoint for details).

Change in parameters related to hypothyroidism (thyroid hormones, creatinine kinase, cholesterol,ultra sensitive CRP, creatinine).

Inclusion Criteria: Differentiated thyroid cancer treated by thyroidectomy and at least 1 ablation with 131-I > 5 months ago TSH < 4 imU/L Exclusion Criteria: Pregnancy Known metastasis