Case Presentation: A 70-year-old male with a past medical history of hypertension and diabetes was sent to the emergency room by primary care physician because of persistent hypokalemia while taking oral potassium supplements. Patient reported generalized weakness, low back pain, thirty-pound weight loss and poor appetite for a few months. He smokes one packet of cigarettes per day. Labs showed potassium 2.1, bicarbonate 33, AST/ALT 189/74, bilirubin 1.4 and platelet count 69,000. Initial CT abdomen pelvis without contrast showed several masses within the liver. Further evaluation of CT chest abdomen with intravenous contrast showed extensive mediastinal adenopathy, bilateral supraclavicular adenopathy and liver metastases. He underwent fine-needle aspiration of supraclavicular lymph node which revealed small cell lung carcinoma. ACTH level was 262 pg/mL (reference range:7.2 – 63.3 pg/mL ) and early morning cortisol was 49.9 ug/dl. Hypokalemia slightly improved with potassium supplements and spironolactone during the hospitalization. MRI of the brain showed multiple small punctate infarctions throughout the cerebrum which were attributed due to malignancy-associated hypercoagulable state as echocardiogram was normal and no arrhythmias were detected on telemetry monitoring. After discussing with the oncologist, the patient and his family decided to pursue hospice care at home, he passed away within a few days after discharge.
Discussion: Hypokalemia is frequently associated with diuretic use and gastrointestinal losses. Refractory hypokalemia can occur with urinary losses due to increased mineralocorticoid activity. Small cell lung cancer is a neuroendocrine tumor account for about 15 percent of all lung cancers. Ectopic adrenocorticotropic hormone (ACTH) syndrome is seen in 2 to 5% of patients with small cell lung cancer. Patients can present with hypokalemia and metabolic alkalosis without typical cushingoid features like purple striae, buffalo hump due to the rapid onset and aggressive nature of cancer. Studies show that small cell lung cancer patients with ectopic ACTH production have an overall poor prognosis. For patients with nonresectable tumors who are receiving chemoradiation therapy, medications such as ketoconazole, metyrapone and spironolactone are used in the treatment of hypercortisolism.
Conclusions: Cancer related paraneoplastic syndromes must be considered in differential diagnosis while evaluating patients with refractory electrolyte abnormalities such as hyponatremia and hypokalemia. The importance of age appropriate cancer screening must be emphasized at every opportunity as a timely diagnosis can help in initiating treatment.