Context: Small cell prostate cancer has rarely been reported in associated with ectopic secretion of adrenocorticotropic hormone (ACTH) and severe clinical Cushing’s syndrome.
Case description: A 91 year old man presented with hypertension and peripheral oedema. His background history consisted of hypertension, type 2 diabetes, atrial fibrillation, transient ischaemic attack, and prostate carcinoma with resection. On examination he had upper limb bruising, centripetal obesity and moderate pitting oedema. He was found to have a metabolic alkalosis, hypokalaemia (K+ 2.4 mmol/L) and initially received intravenous potassium followed by oral replacement.
Investigations revealed markedly elevated morning serum cortisol and ACTH, and non-suppression on a 1mg dexamethasone suppression test. Imaging of his brain, chest, abdomen, and pelvis were normal. Further evaluation of the presumed ectopic secretion of ACTH was not undertaken because of the frailty of the patient and his clearly expressed wishes. Bilateral adrenalectomy was also considered but declined.
Management consisted of ongoing potassium replacement and Ketoconazole 400mg/day commenced with the aim of inhibiting cortisol synthesis. This led to an improvement in serum potassium but was poorly tolerated. Metyrapone 500mg/day was also trialled but ceased due to the development of abdominal pain and diarrhoea. There was little improvement in overall health and the patient opted for medication withdrawal. Post mortem examination revealed high-grade small cell prostate carcinoma, which is a very rare cause of ectopic ACTH.
Conclusions: In difficult to treat hypokalaemic alkalosis the differential diagnosis of ectopic ACTH Cushing's syndrome should be considered. Whilst most causes of ectopic ACTH secretion are found within the chest it is important to contemplate other aetiologies such as prostate cancer.