An Unlikely Cause of Hypokalemia

Hypokalemia is a common clinical disorder caused by a variety of different mechanisms. Although the most common causes are diuretic use and gastrointestinal losses, elevated cortisol levels can also cause hypokalemia through its effects on the renin-angiotensin-aldosterone system. Cushing's syndrome refers to this general state of hypercortisolemia, which often manifests with symptoms of generalized weakness, high blood pressure, diabetes mellitus, menstrual disorders, and psychiatric changes. This syndrome is most commonly caused by exogenous steroid use, but other etiologies have also been reported in the literature. Ectopic adrenocorticotropic hormone production by small-cell lung cancer is one rare cause of Cushing's syndrome, and may be associated with significant hypokalemia.

We describe the case of a 62-year-old man who presented to the emergency department with weakness and hypokalemia. The patient was initially misdiagnosed with furosemide toxicity. Despite having a 30-pack-year smoking history, this patient's lack of respiratory complaints allowed him to present for medical attention twice before being diagnosed with lung cancer. It was later determined that this patient's hypokalemia was due to Cushing's syndrome caused by ectopic adrenocorticotropic hormone production from small-cell lung cancer. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: This case reminds emergency physicians to consider a broad differential when treating patients with hypokalemia. More importantly, it prompts emergency physicians to recognize comorbid conditions and secondary, less common etiologies in patients with repeated visits for the same complaint.