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Chapter 17: The Kidney in Malignancy

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You are referred a patient for evaluation of hypomagnesemia on cetuximab therapy. The patient is a 59-year-old male patient with metastatic colon cancer previously treated failed FOLFOX therapy and now started on cetuximab. He has been complaining of fatigue and muscle weakness. His electrolytes reveal a potassium level of 3.2 mg/dL and magnesium of 0.9 mg/dL. He has a high fractional excretion of magnesium. What are the risk factors for the development of hypomagnesemia with cetuximab therapy?

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A. Duration of therapy

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B. Race (African–American)

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C. Elderly

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D. Chronic kidney disease

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E. A and C

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The answer is E. Cetuximab, a monoclonal antibody against epithelial growth factor receptor (EGFR) is known to cause hypomagnesemia. This happens as a result of reduction in the transport of transient receptor potential melastatin (TRPM) 6/7 ion channels to the apical membrane of the distal renal tubule. Filtered magnesium (Mg) is reabsorbed mainly in the thick ascending limb of Henle and the distal tubule, where most of the EGFR is located in the kidney. Epidermal growth factor is an autocrine paracrine hormone that regulates renal Mg reabsorption by regulating the activity and transport of TRPM6. Blocking EGFR with cetuximab blunts the movement of TRPM6/7 channel, which leads to renal Mg wasting and hypomagnesemia. The main risk factors for developing hypomagnesemia are duration of treatment, age, and baseline Mg values. Hence, choice E is correct.

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An elderly gentleman who has CLL comes for a route clinic visit. He has no complaints. His blood work reveals a WBC of 190,000/mL and mild thrombocytopenia. The serum potassium level is 8.5 mEq/L. The patient is sent to emergency room for evaluation. The repeat potassium is 2.5 mEq/L. There are no ECG changes and physical examination and history are unremarkable. What should be done next?

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A. Admit for IV potassium repletion

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B. Request a plasma K level

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C. Give sodium polystyrene and place on low K diet

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D. Admit to telemetry floor

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The answer is B. This is a case of spurious hyperkalemia and hypokalemia. For patients with very elevated WBCs, the cells can lyse in the test tube, producing hyperkalemia. Pseudohypokalemia can also occur since the cells are metabolically active and can take up potassium while in the test tube. A plasma sample should provide a more accurate read of the serum potassium. Choice B is correct.

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A 65-year-old male patient with history ...

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