Review of clinical data from 350 patients with
small-cell lung cancer (SCLC) revealed
hyponatremia (
sodium less than 130 mEq/L) attributable to the syndrome of inappropriate secretion of
antidiuretic hormone (
SIADH) in 40 patients (11%). Although
hyponatremia was severe in most instances (median,
sodium 117 mEq/L), symptoms attributable to
water intoxication were identified in only 27% of hyponatremic episodes. Development of
SIADH showed no correlation with clinical stage, distribution of metastatic sites, sex, or histologic subtype of
small-cell carcinoma.
SIADH occurred most often with initial presentation (33 of 40), and resolved promptly (less than 3 weeks) with initiation of
combination chemotherapy in 80% of evaluable patients. The presence of
SIADH did not influence response to
chemotherapy or overall survival as an independent variable. However, in five patients profound
hyponatremia developed immediately following primary cytotoxic
therapy (range, one to five days). Despite initial control of
SIADH, dilutional
hyponatremia recurred in 70% of patients with
tumor progression. Our findings suggest that development of clinically demonstrable
SIADH in patients with SCLC is dependent on functional properties of the neoplastic cells, rather than
tumor burden or metastatic site. The potential for development of clinically significant
hyponatremia early in the course of cytotoxic
therapy emphasizes the need to closely monitor patients, particularly those receiving
chemotherapy regimens requiring substantial intravenous hydration.