[A case of hyperthyroidism due to functioning metastasis of differentiated thyroid carcinoma. Discussion and literature review].

We report on a very rare case of hyperthyroidism due to multiple autonomously functioning bone metastasis of papillary thyroid cancer in a 79-year-old woman. This situation remains extremely uncommon, as shown by our review of the literature; only 47 similar cases have been published from 1946 to 2005. The pathogenic mechanism remains largely unknown in spite of several hypotheses (conjunction in volume and differentiation, auto-antibodies). Hyperthyroidism can be severe, and often T3 levels are markedly more elevated than T4 levels. Apart from hyperthyroidism caused by the hormone-production, clinical features are similar to that of usual metastatic thyroid cancer, occurring in elderly women in most cases, and of follicular type on pathology. Metastases mostly occur in bones and lungs. Treatment relies mainly on radio-iodine ((131)I), which is efficient on hormonal disorders, and prognosis appears to be correlated with the ability of the metastatic sites to concentrate radio-iodine.