Symptomatic hyponatremia induced by low-dose cyclophosphamide in patient with systemic lupus erythematosus: A case report.

RATIONALE Cyclophosphamide (CY) is an alkylating agent used widely to treat cancer and autoimmune diseases. Hyponatremia is a common adverse effect of high-dose and moderate-dose of intravenous CY, but is rare in patients treated with low-dose (<15 mg/kg). PATIENT CONCERNS A 52-year-old woman with new-onset systemic lupus erythematosus (SLE) was treated with low-dose cyclophosphamide (8 mg/kg, CY), but showed sudden headaches, disorientation and weakness. Laboratory examinations revealed severe isovolumic hyponatremia along with low-serum osmolality and high urine osmolality. DIAGNOSIS The acute hyponatremia was consistent with the syndrome of inappropriate antidiuretic hormone secretion (SIADH) and was an adverse event of low-dose CY, with no evidence of endocrine, cancer, pulmonary, or cerebral abnormalities relevant to the SIADH. INTERVENTION The hyponatremia was resolved after the supplementation of NaCl solution. OUTCOMES The hyponatremia was resolved without any complications. LESSONS Hyponatremia induced by low-dose CY should be recognized as an underlying life-threatening complication in clinical practice.