[Lithium therapy and hyperthyroidism: disease caused or facilitated by lithium? Review of the literature apropos of a case of hyperthyroidism preceded by transient hypothyroidism].

A case of hyperthyroidism occurring in a 68 year old man receiving lithium carbonate (1 g/day) for 5 years is reported. The clinical history of the patient, treated for bipolar affective disorder, was remarkable for transient hypothyroidism followed several months later by tremor, increased free thyroxine and triiodothyronine, and decreased TSH levels which led to lithium withdrawal. Two months later, clinical and biological signs were unchanged, Tc99m-scan displayed a homogeneous and increased isotope uptake. In this setting, high levels of autoantibodies against TSH-receptor, and grade I exophthalmos and slightly ocular muscle enlargement at CT-scan favored the diagnosis of Graves' disease (perhaps facilitated by lithium therapy). Carbimazole treatment was effective in controlling hyperthyroidism. Review of the literature disclosed 44 cases of hyperthyroidism occurring in lithium-treated patients. Most of these cases concerned specific thyroid diseases, particularly with an autoimmune mechanism. There is also evidence for an actual role of lithium in increasing intrathyroid iodide pool and for an impact of lithium on the immune system. Thus, the hypothesis that lithium may trigger the development of an autoimmune thyroid disease in predisposed patients deserves further investigation.