Mifepristone Increases Thyroid Hormone Requirements in Patients With Central Hypothyroidism: A Multicenter Study

PURPOSE: Mifepristone is a glucocorticoid and progesterone receptor blocker that can be used for patients with hyperglycemia and Cushing syndrome in whom surgery failed to achieve remission or who were ineligible for surgery. We report a case series of patients with Cushing disease (CD) and central hypothyroidism that presented with increased levothyroxine requirements during mifepristone therapy. METHODS: Retrospective longitudinal case series of patients with CD and central hypothyroidism treated with mifepristone in a retrospective database at four pituitary centers in the United States. RESULTS: Five patients with CD were found, all women, median age 50 (interquartile range 47 to 64.5). They received mifepristone because no adequate response or intolerance to other drugs was observed. Mifepristone initiation was associated with a decrease in free thyroxine levels, mandating a dose increase of a median 1.83 (1.71 to 3.5) times the initial dose of levothyroxine to achieve normal levels. Weight loss was seen in four of five patients, ranging from 3.2 to 42.6 kg in up to 54 months of follow-up. CONCLUSIONS: Although the mechanism behind the decrease in thyroid hormone level is unknown, intestinal malabsorption, decreased residual thyroid function and increased inactivation of T4 via deiodinases are all potential causes. Whereas therapies for hypercortisolism aim to decrease features of hypercortisolemia such as weight gain and depression, hypothyroidism can hamper these goals. This case series raises awareness on the importance of assessment of thyroid status in patients receiving mifepristone to optimize clinical outcomes.