Cyclophosphamide-Induced Severe Acute Hyponatremic Encephalopathy in Patients with Breast Cancer: Report of Two Cases

BACKGROUND: Cyclophosphamide is an alkylating agent widely used in antineoplastic and immunosuppressive therapies. Symptomatic hyponatremia can be a rare but life-threatening complication in patients treated with cyclophosphamide. CASE PRESENTATIONS: We report 2 patients who presented with severe acute hyponatremic encephalopathy after receiving their first cycles of a low-dose cyclophosphamide-containing regimen for breast cancer. In case 1, a 58-year-old female received the combination of docetaxel and cyclophosphamide, and in case 2, a 56-year-old female received the combination of doxorubicin and cyclophosphamide. Both patients recovered after correction of their serum sodium concentration without neurological deficits. Future cycles of chemotherapy were well tolerated without recurrence of hyponatremia after cyclophosphamide was discontinued from the respective regimens. CONCLUSION: Clinicians must always keep in mind that acute hyponatremic encephalopathy can be induced by low-dose cyclophosphamide.