Paraneoplastic Cushings syndrome due to prostate cancer: a rare occurrence
Subash Sivaraman & David Jenkins
We present the case of a 72-year-old gentleman was admitted to our hospital with atrial fibrillation secondary to severe hypokalemia of 1.8 mmol/l, but normal serum sodium and creatinine. He had prostate cancer with extensive liver and bone metastases. After potassium supplementation 180200 mmol/day for 10 days serum levels persisted between 2.3 and 2.9 mmol/l. During this short period he developed early Cushingoid features, jaundice and diabetes. After overnignt dexamethasone 1 mg, his serum cortisol was 1988 nmol/l with corresponding ACTH of 434 ng/l (046). Free cortisol in 24 h urine was >2942 nmol/l (<350). We treated him with metyrapone which normalised potassium levels at 3.7 mmol/l within 4 days enabling us to stop supplements. Unfortunately he died from metastatic prostate cancer 6 weeks after initial presentation.
Cushings syndrome as a paraneoplastic manifestation of prostate cancer is rare and prognosis after its onset is poor, survival ranging from a few days to 3.5 months in various case reports. We used metyrapone as it is short acting, has few adverse effects and is effective in doses from 250 mg to 6 g daily thus lending itself to precise titration. Prolonged therapy with metyrapone can cause production of adrenal androgens which could be detrimental in a patient with prostate cancer. However it is unlikely to be significant in this setting where the life expectancy is very short.
There is one previous case report of metyrapone being successfully used as single agent to control steroid excess in the setting of prostate cancer. Metyrapone is underused probably because of restricted availability and unfamiliarity of oncologists with the drug.