Severe Cushing's syndrome from an ectopic adrenocorticotropic hormone-secreting neuroendocrine tumour treated by osilodrostat.

Summary: Severe Cushing's syndrome from an ectopic adrenocorticotropic hormone-producing tumour is rare but often demands rapid diagnostics and treatment of hypercortisolism with its comorbidities. Pharmacotherapy of hypercortisolism by ketoconazole, metyrapone and osilodrostat is currently available. If unsuccessful or insufficient a bilateral adrenalectomy is an option. We present a 28-year-old female with severe Cushing's syndrome caused by a bronchial metastatic neuroendocrine tumour (NET). Hypercortisolism was efficiently treated by osilodrostat with block-replace and then titration regimen. A once-daily dose was finally used with normalised cortisol levels. Androgen levels measured by liquid chromatography-mass spectrometry were slightly elevated during the treatment but without any symptoms. A simple once-daily use of osilodrostat with titration regimen led to normalised cortisol levels in a severe Cushing's syndrome patient with an uncurable bronchial NET. Transient hypocortisolism during treatment appeared but was easily treated by hydrocortisone. Learning points: Cushing's syndrome from an ectopic adrenocorticotropic hormone-producing tumour is rare. Cortisol upregulation is often severe and rapid, though clinical signs are not always fully pronounced. Rapid treatment is a key for preventing and reducing complications such as fractures, thromboembolism, bleeding, hyperglycaemia, and arterial hypertension. The novel potent steroidogenesis inhibitor osilodrostat can be used as first-line treatment for reducing hypercortisolism.