The histopathologic features of lithium-associated thyroiditis.

The case of a 62-year-old woman with lithium-associated thyroiditis is presented. Lithium can produce goiters associated with hypothyroidism and, less commonly, hyperthyroidism and euthyroidism. The characteristic histopathologic features of the affected thyroid gland included fibrosis, lymphoid follicles with atrophy, and hyperplasia of thyroid follicles. The pathogenetic mechanism appears to be immunologic, with lithium acting as a haptene with a thyroid antigen to induce an "autoimmune" type of thyroiditis.