A case report of osilodrostat treatment in primary bilateral macronodular adrenal hyperplasia associated with bilateral adrenal mass reduction

Abstract Primary bilateral macronodular adrenal hyperplasia (PBMAH) is a rare cause of Cushing syndrome (CS), characterized by bilateral adrenal nodules larger than 1 cm. Cortisol hypersecretion in PBMAH is driven by intra-adrenal rather than pituitary adrenocorticotropic hormone (ACTH), with its pathogenesis mediated by aberrant hormone receptor expression in the adrenal cortex. This article reports a case of a 60-year-old woman with PBMAH in whom a marked reduction in bilateral adrenal masses was observed following treatment with osilodrostat. The patient presented with typical Cushingoid features, accompanied by hypertension, diabetes mellitus, osteoporosis, and severe restrictive lung disease. Genetic testing identified a pathogenic mutation in the ARMC5 gene, confirming the diagnosis. Because she was intolerant of surgical treatment, left adrenal artery embolization (AAE) was performed but failed to control hypercortisolism. Osilodrostat therapy was subsequently initiated—this potent 11β-hydroxylase inhibitor was recently approved in China for the treatment of Cushing syndrome. Notably, after 23 weeks of treatment, the patient's 24-hour urinary free cortisol (24 hours-UFC, CLIA) level returned to normal. Treatment was then discontinued, and during 11 months of follow-up the patient’s 24 hours-UFC remained within the normal range. Moreover, imaging performed during the period of osilodrostat therapy demonstrated significant shrinkage of both adrenal glands. To our knowledge, this is the first reported case of bilateral adrenal mass reduction observed in temporal association with osilodrostat treatment in a PBMAH patient. However, prior AAE confounds the attribution of tumor shrinkage to osilodrostat alone. These findings highlight an observed association between the drug and mass reduction, warranting further investigation to clarify its potential role beyond symptomatic control.