Morphological studies in a case of thyrotoxicosis complicated by lithium therapy for bipolar depression

The histological and ultrastructural features of the thyroid in a case of thyrotoxicosis complicated by lithium therapy (for bipolar depression) are described. Despite the bizarre and disturbing pathological appearances, it is proposed that their interpretation should be modified in view of the biosynthetic block imposed by lithium administration. The cellular appearances are considered to reflect a hyperplastic state with coincidental impairment of synthetic activity, and not to represent a neoplastic process. The use of lithium in the management of psychiatric illness is increasing. It is important to be aware of the possible effect of the drug not only on thyroid function but also on the histopathological appearances of the thyroid when interpreting any associated or incidental lesion of the gland.