[Paraneoplastic Cushing's syndrome as cause of refractory hypokalemia]

A 58-year-old man presented with refractory hypokalemia and rapid weight gain. On examination, he had high blood pressure, central obesity and bilateral pitting edema.

Biochemical tests showed hypokalemic metabolic alkalosis due to ACTH-dependent hypercortisolism. CT of thorax and abdomen revealed a pulmonary and a right adrenal mass. Biopsy of the pulmonary mass led to the diagnosis of an ACTH-producing small cell lung cancer.

Under treatment with ketoconazole and chemotherapy a tumor response was reached and the hypercortisolism was controlled. Since the right adrenal mass remained stationary under chemotherapy, an incidental adrenal adenoma seemed the most likely diagnosis.

The diagnosis of paraneoplastic Cushing's syndrome can be challenging, since classical clinical features of hypercortisolism may still be absent, even if the underlying cancer is already advanced. Therefore high clinical suspicion is warranted, especially in patients presenting with new-onset refractory hypokalemia, metabolic alkalosis and arterial hypertension.