[Silent thyroiditis in a patient under lithium therapy]. / Thyroïdite silencieuse chez un patient traité par lithium.

While hypothyroidism secondary to treatments by lithium are well known, cases of hyperthyroidism are less common. A 48 years old patient under lithium carbonate from about 10 years ago presents hyperthyroidism without any auto-immunity biological markers, associated with a very low thyroid tracer uptake on scintigraphy. Treatments by anti thyroid agents will be necessary during months in order to normalize the hormone level, whereas lithium is maintained. Only few tens of cases of hyperthyroidism related to lithium have been reported in the literature. This observation shows the importance of the thyroid hormonal follow up for patients under lithium, in order to treat them before the outbreak of a thyroid dysfunction. The causal toxic mechanism is still unclear, and may be related with a direct damage of lithium to follicular cells.