[Severe Hyponatremia as a Marker of Malignancy in Patients with Liver Cirrhosis. Clinical Implications and Prognostic Relevance in Two Cases].

Severe hyponatremia is a common complication (21.6%) in patients with decompensated cirrhosis. It can sometimes manifest as a paraneoplastic syndrome, which may precede the diagnosis of cancer in 5% of cases. It can be associated with lung cancer (25 - 45%), colorectal cancer, breast cancer, or lymphomas. Hyponatremia reflects the complexity of the interactions between liver disease and oncological processes. In decompensated cirrhotic patients, hyponatremia is usually caused by the kidney´s inability to excrete free water, resulting in dilution of blood sodium. However, in the context of cancer, factors such as ectopic antidiuretic hormone secretion by tumors can exacerbate this condition. This inappropriate antidiuretic hormone secretion can lead to additional water retention, worsening the hyponatremia in these patients. We present two clinical cases that illustrate this relationship: a patient with liver metastases and a patient with pulmonary nodules, both with compensated cirrhosis as a chronic disease, who were admitted with severe hyponatremia. The management of these patients requires a multidisciplinary approach, searching for occult neoplasms and carefully normalizing sodium levels to prevent neurological complications. Early identification of hyponatremia is crucial due to its prognostic impact.