Apparent Mineralocorticoid Excess in a Case of Lung Paraneoplastic Cushing Syndrome

Severe hypokalemia is a life threatening event, which triggers a number of therapeutic and diagnostic attitudes. In this paper we present a case of 63 years old man, who presented with progressive lassitude, edema, weight loss. The mild hypertension and hyperglycaemia were treated with spironolactone and diet. Initial evaluation showed severe hypokalemia (1.7 mmol/l), hepatomegalia, hyperplasic/nodular adrenal masses; in addition, he has developed a right middle lobe pneumonia which improved with antibiotics. Referred for the suspicion of hyperaldosteronism, aldosterone values were normal (9.3-9.5 μg/dl), but ACTH was high (725 pg/ml) and did not suppress (710.8 pg/ml) to high dose DXM, as well as cortisol: basal values 27.78 ug/dl, high dose DXM 35.06 ug/dl, showing an ACTH dependent Cushing syndrome despite lack of suggestive clinical signs. Tumor markers suggested a neuroendocrine neoplasia: carcinoembryonic antigen=101 ng/ml (normal values=0.52-6.3 ng/ml), CA 19-9= 155 ng/ml (N < 33 ng/ml). Further radiological evaluation showed a 3 cm right lobe lung tumour. Despite high potassium supplements and spironolactone, the hypokalemia remained around 3.2 mmol/l, characteristic for an apparent mineralocorticoid excess. Because of aggressive evolution of the lung tumour, he died three months after the initial admission into the hospital. Pathology report showed a lung carcinoma. ACTH immunostaining of the lung tumour was positive and revealed a paraneoplastic secretion.