SERUM TSH AND THE RESPONSE TO RADIOIODINE TREATMENT OF TOXIC MULTINODULAR GOITER

A retrospective analysis of data from 73 consecutive patients with tox ic multinodular goitre treated with iodine-131 (I-131) during a 2-year period was performed to investigate if serum TSH at the time of I-131 treatment influences the outcome. The dose of I-131 was calculated ac cording to a model compensating for thyroid size estimated by palpatio n and 24-h I-131 uptake. Serum TSH was determined by a third-generatio n assay with a functional sensitivity of 0.03 mU/l. A significantly mo re pronounced response to I-131 treatment was observed in patients wit h TSH>0.0 mU/l than in patients with TSH=0.0 mU/l (P = 0.0006). This d ifference resulted in a threefold lower frequency of non-responders an d a fivefold higher rate of early hypothyroidism in the group with det ectable serum TSH. While the high frequency of hypothyroidism among pa tients with measurable serum TSH can be explained by destruction of no rmal thyroid tissue, the high frequency of treatment failure in the gr oup with serum TSH=0.0mU/l suggests that autonomous thyroid tissue may also be sensitized to a deleterious effect of I-131 through stimulati on by TSH. We conclude that serum TSH has a significant influence on t he outcome of I-131 treatment of toxic multinodular goitre. The result s of I-131 treatment may be improved by adjustment of the dose of I-13 1 according to the serum TSH level, in addition to adjustment for goit re size and 24-h I-131 uptake.