Hyponatremia in oncology – often unrecognized, but therapeutically relevant
12.07.2016 11:46
Dr. Helge Bischoff, senior consultant at the Thorax Clinic in Heidelberg, believes it is essential to recognize and adequately treat existing hyponatremia, as he emphasized in a media workshop supported by Otsuka Pharma. Hyponatremia is an often serious electrolyte imbalance that occurs in 15–30 percent of hospitalized patients. In approximately one-third of cases, hyponatremia is triggered by a syndrome of inappropriate antidiuretic hormone secretion (SIADH). Possible causes of SIADH include cancer, particularly of the lungs.
Hyponatremia isn't just a laboratory finding—according to Bischoff, it also increases mortality. Hyponatremia can be hidden behind nonspecific symptoms, ranging from mild weakness to severe general or central nervous system disorders. Due to the variability of symptoms, it often goes undetected and therefore untreated, Bischoff explained. This is despite the fact that hyponatremia can prolong hospital stays and also increase the risk of mortality.
Approximately 15–22% of all hospitalized patients have mild hyponatremia (serum sodium 130–134 mmol/L), 7% have moderate hyponatremia (125–130 mmol/L), and approximately 3% have severe hyponatremia (≤ 125 mmol/L). Hyponatremia that develops acutely in less than 48 hours is an emergency and must be treated immediately, explained Bischoff, as it can lead to cerebral edema. If the electrolyte imbalance develops slowly (> 48 hours), symptoms such as fatigue, confusion, loss of appetite, and personality changes are predominant. However, even mild cases are frequently accompanied by gait disturbances with an increased risk of falls and fractures.
According to Bischoff, the cause of over 30% of hyponatremia cases is SIADH. This is a disorder of osmoregulation characterized by pathologically increased secretion of antidiuretic hormone (ADH). This leads to water retention and resulting dilutional hyponatremia. Carcinomas—particularly of the lungs—can trigger SIADH, but other lung diseases (including infections, asthma, COPD), CNS disorders, and medications (including cytotoxic drugs, psychotropic drugs, and analgesics) are also possible causes.
Bischoff presented his clinical experience with the use of “Samsca” (tolvaptan) in patients with lung cancer.
Treatment of SIADH in lung cancer has a positive impact on overall survival
According to Bischoff, hyponatremia in cancer patients not only leads to shorter survival times, but also to delays or limitations in chemotherapy and a deterioration in general health. 11–15 percent of patients with small cell lung cancer (SCLC) develop paraneoplastic hyponatremia, which has an unfavorable prognosis, due to SIADH. Approximately 2.7 percent of patients with non-small cell lung cancer (NSCLC) are also affected by this during the course of their disease, Bischoff emphasized. He cited chemotherapeutic agents, immunomodulators, and opioids as risk factors that can cause or exacerbate hyponatremia in cancer patients, as well as nausea, vomiting, stress, and fluid overload during infusion therapy.
Bischoff reported that a retrospective analysis of patients with lung cancer (SCLC, NSCLC) demonstrated the importance of timely and effective treatment of hyponatremia due to SIADH. Normalization of serum sodium levels above 138 mmol/L led to a significant increase in the median survival time of these patients compared to the group without correction of sodium levels above 138 mmol/L (13.3 vs. 5.2 months; p = 0.007).
Treatment of SIADH-induced hyponatremia with “Samsca” reduces the need for fluid restriction and can improve the patient’s general condition before chemotherapy.