RESUMEN
INTRODUCTION: The small cell lung cancer (SCLC) is a rapidly progressive malignancy with a poor prognosis. Its chemosensitivity mandates prompt treatment. Hyponatremia occurs frequently in patients with small cell lung cancer due to the syndrome of inappropriate antidiuretic hormone (SIADH). We report a case of severe hyponatremia induced by chemotherapy that required management in intensive care. OBSERVATION: A 68-year-old patient was undergoing treatment for small cell cancer, invading the right lung. On the second day of the first cycle of treatment (cisplatine-vepeside), the patient became comatose and required transfer to an intensive care unit. The coma was due to severe hyponatremia (107 mmol/L) and improved with specific treatment. The patient had similar episodes on the second day of each chemotherapy treatment but with less and less severe clinical manifestations. Hyponatremia due to chemotherapy in SCLC is not commonly known; a relation between hyponatremia intensity and the tumor size is suspected. CONCLUSION: This clinical case highlights the possibility of severe hyponatremia during small cell lung cancer chemotherapy. Hyponatremia may be related to the reduction in tumor size. Monitoring of electrolytes on day 2 of chemotherapy is advised.