Background
Hypothyroidism is a common condition that is frequently irreversible and requires lifelong thyroid replacement therapy.
Objective
To assess the incidence and factors that can predict reversibility of hypothyroidism caused by Hashimoto's thyroiditis.
Methods
We studied 79 patients in whom Hashimoto's thyroiditis was diagnosed according to suggestive cytologic features and/or the presence of thyroid antibodies (antimicrosomal antibody titer, 
1:1600; antiglobulin antibody titer, 1:400). All patients were initially hypothyroid (serum total thyroxine level, 83.5±28.6 nmol/L [6±2 µg/dL]; thyrotropin level, 24.7±28.3 mU/L). Levothyroxine sodium was then administered for 1 year to normalize results of thyroid blood tests. Thereafter, the treatment was stopped for 3 weeks and serum thyrotropin and total thyroxine concentrations were determined.
Results
After withdrawal of levothyroxine treatment, thyroid blood tests showed that the degree of hypothyroidism worsened in 20 patients, remained unchanged in 40, and improved in 19. Nine patients (11.4%) did show normalization of the thyroid blood tests. Before treatment, the presence of the following in a patient—of a goiter that is 35 g or larger, thyrotropin levels greater than 10 mU/L, and an anamnestic familial incidence of thyroid disease— was clearly associated with an increased incidence of recovery of normal thyroid function (relative risk, 5.4; 95% confidence interval, 2.8 to 10.7; P<.0002).
Conclusions
Our results confirm that hypothyroidism caused by Hashimoto's thyroiditis is not always permanent. The presence of a larger goiter and high thyrotropin levels at the time of diagnosis, associated with a familial incidence of thyroid disease, may be related to an increased incidence of hypothyroidism remission.
(Arch Intern Med. 1995;155:1404-1408)
