A case of prolonged adrenal insufficiency following osilodrostat discontinuation with a review of the literature.

Osilodrostat is an oral steroidogenesis inhibitor used in the treatment of hypercortisolism. It works by inhibiting 11-beta-hydroxylase, a key enzyme in cortisol synthesis. As a consequence of drug action, adrenal insufficiency can be observed in about 40% of patients. Although this effect has been accepted as a consequence of therapy, recent reports suggest adrenal insufficiency can persist even after discontinuation of osilodrostat. We present the case of a 74-year-old female patient who developed prolonged adrenal insufficiency after withdrawal of osilodrostat. The patient was diagnosed with ectopic ACTH-dependent Cushing's syndrome and underwent radiotherapy for a primary lesion located in the anterior mediastinum. During treatment, osilodrostat was introduced (2 to 4 mg/d), and adrenal insufficiency developed within four weeks. Hydrocortisone (intermittently dexamethasone) replacement therapy was initiated, and over time, undetectable morning cortisol levels continued. After de-escalating the osilodrostat dose, the drug was withdrawn 15 months after initiation. Despite being off the drug for 11 months, the patient with adrenal insufficiency (morning serum cortisol: 37.2 nmol/L), still requires hydrocortisone substitution. The underlying mechanism of prolonged adrenal insufficiency after osilodrostat discontinuation remains unclear. It is unknown whether this is due to permanent inhibition of 11-beta-hydroxylase or interference at another step in steroidogenesis. Factors such as treatment duration, dose, or individual sensitivity may play a role, but other mechanisms, such as an adrenolytic effect, should also be considered. We expect an increase of similar cases, which we believe will lead to further research to better understand the mechanisms behind prolonged adrenocortical blockade after osilodrostat discontinuation.