SIADH: differential diagnosis and clinical management

Despite the widespread prevalence of hyponatremia and its deleterious effects on patients, it is often overlooked and consequently undertreated. This set of four cases provides practical advice on how to identify, diagnose, and treat patients with syndrome of inappropriate antidiuretic hormone (SIADH). The first steps that a physician should take when diagnosing a patient with hyponatremia are to assess the severity of neurological symptoms, and check the patient's volemic status in order to determine whether emergency treatment with hypertonic saline is indicated. Laboratory tests are necessary for the diagnosis of SIADH, but, in severe, symptomatic cases of hyponatremia, patients need treatment before the results of laboratory tests can be obtained. In this series, Case 1 demonstrates how awareness of hyponatremia led to early diagnosis and treatment. Case 2 demonstrates how multiple causes of hyponatremia can be diagnosed and managed sequentially. Case 3 illustrates how a patient with severe symptoms should be treated while waiting for laboratory test results to confirm diagnosis. Case 4 examines how the priorities of a patient should inform the management of their chronic SIADH, using palliative care of a patient with small-cell lung cancer as an example. There are several factors that clinicians should consider when making treatment decisions, including signs and symptoms, risks and benefits of different treatments, psychosocial factors, and the patient's wishes. All the available treatment options have a place in the management of patients with SIADH, and a physician should individualize decisions based on a patient's needs and priorities.