An 81-years-old gentleman presented with a 2-week history of reduced appetite, lethargy and 2-3 kg weight loss over the previous one month. Routine investigations identified a potassium of 2.2 mmol/L. He was admitted for IV potassium replacement. His repeat potassium level after 3 days, was less than 2.9 mmol/L. His admission chest radiograph showed a suspicious lung lesion. A CT chest was arranged and revealed a left lower lobe lesion, consistent with a new malignancy, suspicious of a small cell lung cancer. Further biochemical and hormonal assays increased suspicions of an ACTH secreting carcinoid tumour. A PET scan, identified increased uptake of FDG in the lung lesion. Tumour histology was positive for ACTH, synaptophysin, chromogranin A and CD56 secretion. Proliferation index assessed with Ki67 was less than 1%. Chromogranin A was elevated, and Urine 5-HIAA testing was positive. A 24-hour free cortisol excretion test was elevated at 213 mmol/L. He was not a surgical candidate. Subsequently, he functionally deteriorated and was referred to the palliative team.

Keywords: Hypokalaemia; Carcinoid lung cancer; Cushing’s syndrome; Carcinoid syndrome