Managing hyponatremia in patients with syndrome of inappropriate antidiuretic hormone secretion

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.

Clinical aspects of symptomatic hyponatremia

Hyponatremia (HN) is a common condition, with a large number of etiologies and a complicated treatment. Although chronic HN has been shown to be a predictor of poor outcome, sodium-increasing treatments in chronic stable and asymptomatic HN have not proven to increase life expectancy. For symptomatic HN, in contrast, the necessity for urgent treatment has broadly been accepted to avoid the development of fatal cerebral edema. On the other hand, a too rapid increase of serum sodium in chronic HN may result in cerebral damage due to osmotic demyelinisation. Recently, administration of hypertonic saline bolus has been recommended as first-line treatment in patients with moderate-to-severe symptomatic HN. This approach is easy to memorize and holds the potential to greatly facilitate the initial treatment of symptomatic HN. First-line treatment of chronic HN is fluid restriction and if ineffective treatment with tolvaptan or in some patients other agents should be considered. A number of recommendations and guidelines have been published on HN. In the present review, the management of patients with HN in relation to everyday clinical practice is summarized with focus on the acute management.

Hyponatremia secondary to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH): therapeutic decision-making in real-life cases

Despite being the most common electrolyte disturbance encountered in clinical practice, the diagnosis and treatment of hyponatremia (defined as a serum sodium concentration <135 mmol/L) remains far from optimal. This is extremely troubling because not only is hyponatremia associated with increased morbidity, length of hospital stay and hospital resource use, but it has also been shown to be associated with increased mortality. The reasons for this poor management may partly lie in the heterogeneous nature of the disorder; hyponatremia presents with a variety of possible etiologies, differing symptomology and fluid volume status, thereby making its diagnosis potentially complex. In addition, a general lack of awareness of the clinical impact of the disorder, a fear of adverse outcomes through overcorrection of sodium levels, and a lack of effective targeted treatments until recent years, may all have contributed to a reticence to actively treat cases of hyponatremia. There is therefore a clear unmet need to further educate physicians on the pathophysiology, diagnosis and management of this important condition. Through the use of a variety of real-world cases of patients with hyponatremia secondary to the syndrome of inappropriate secretion of antidiuretic hormone—a condition that accounts for approximately one-third of all cases of hyponatremia—this supplement aims to provide a comprehensive overview of the challenges faced in diagnosing and managing hyponatremia. These cases will also help to illustrate how some of the limitations of traditional therapies may be overcome with the use of vasopressin receptor antagonists.

Clinical guidelines for management of diabetes insipidus and syndrome of inappropriate antidiuretic hormone secretion after pituitary surgery

Changes in water metabolism and regulation of vasopressin (AVP) or antidiuretic hormone (ADH) are common complications of pituitary surgery. The scarcity of studies comparing different treatment and monitoring strategies for these disorders and the lack of prior clinical guidelines makes it difficult to provide recommendations following a methodology based on grades of evidence. This study reviews the pathophysiology of diabetes insipidus and inappropriate ADH secretion after pituitary surgery, and is intended to serve as a guide for their diagnosis, differential diagnosis, treatment, and monitoring.

SIADH and partial hypopituitarism in a patient with intravascular large B-cell lymphoma: a rare cause of a common presentation

Hyponatraemia is a very common electrolyte abnormality with varied presenting features depending on the underlying cause. The authors report the case of a 75-year-old, previously fit, gentleman who presented with weight loss, lethargy and blackouts. He required four admissions to the hospital over an 8-month period. Investigations revealed persistent hyponatraemia consistent with a diagnosis of syndrome of inappropriate antidiuretic hormone secretion, macrocytic anaemia and partial hypopituitarism. Unfortunately, all other investigations that were performed failed to identify the underlying cause and a diagnosis of intravascular large B-cell lymphoma was only confirmed following postmortem studies. The authors recommend that endocrinologists should be involved at the outset in the management of patients with persistent hyponatraemia and that intravascular large B-cell lymphoma should be considered in the differential diagnosis of hyponatraemia.

Perspectives on the management of hyponatraemia secondary to SIADH across Europe

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is the most common cause of euvolaemic hyponatraemia. However, although first described over 50 years ago, the management of hyponatraemia secondary to SIADH is not always straightforward. Some of the issues surrounding the management of hyponatraemia secondary to SIADH were explored in the European Hyponatraemia Survey completed by attendees of the European Hyponatraemia Network Academy Meeting 2011. This article describes the findings of this survey and the specific issues raised regarding the management of hyponatraemia secondary to SIADH in Europe. Some of these issues - including awareness, education, diagnosis, management and cost considerations of the condition - were common to countries across Europe.

Considerations regarding the management of hyponatraemia secondary to SIADH

Treatment of hyponatraemia secondary to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) should be guided by the symptomatology of the patient, which can be used as a surrogate for the duration of the hyponatraemia. However, in patients with acute symptomatic hyponatraemia (developing in <48 hours), the need to actively treat hyponatraemia is more imperative due to the potential risks associated with leaving hyponatraemia untreated (including the potential for development of serious neurological manifestations, such as seizures and brain stem herniation). In patients with hyponatraemia care needs to be taken not to exceed the recommended rates of correction, as this increases the risk of osmotic demyelination syndrome. This article will discuss the potential impact of prompt intervention in the treatment of hyponatraemia, particularly secondary to SIADH, and the need to weigh the benefits of treatment against the potential risks associated with overly rapid correction.

Evaluation of costs associated with tolvaptan-mediated hospital length of stay reduction among US patients with the syndrome of inappropriate antidiuretic hormone secretion, based on SALT-1 and SALT-2 trials

BACKGROUND

Two randomized clinical trials, the Study of Ascending Levels of Tolvaptan in Hyponatremia 1 and 2 (SALT-1 and SALT-2), showed that tolvaptan was an efficacious and safe therapy for the treatment of hyponatremic patients with the syndrome of inappropriate antidiuretic hormone secretion (SIADH).

HYPOTHESIS

This study evaluated the potential cost savings associated with tolvaptan usage based on the SALT-1 and SALT-2 trials.

METHODS

Hospital length of stay (LOS) reduction associated with tolvaptan versus placebo was evaluated among hyponatremic patients with the SIADH (serum sodium < 135 mEq/L) from the combined data of the SALT-1 and SALT-2 trials. The Healthcare Cost and Utilization Project 2009 Nationwide Inpatient Sample database was used to estimate hospital cost and LOS for hospitalizations of adult (age ≥ 18 years) patients with the SIADH. A cost-offset model was constructed to evaluate the impact of tolvaptan on hospital cost and LOS, with univariate and multivariate Monte Carlo sensitivity analyses.

RESULTS

In the SALT-1 and SALT-2 trials, patients with the SIADH receiving tolvaptan had a shorter hospital LOS than patients receiving placebo (4.98 vs 6.19 days, respectively). There were 21 718 hospitalizations for the SIADH identified from the Healthcare Cost and Utilization Project Nationwide 2009 Inpatient Sample database, with a mean LOS of 5.7 days and mean total hospital costs of $8667. Using an inpatient tolvaptan treatment duration of 4 days, with a daily wholesale acquisition cost of $250, the cost-offset model estimated an LOS reduction among SIADH hospitalizations of 1.11 days. The total cost offset, including tolvaptan drug cost, was estimated to be $694 per admission. The cost-neutral break-even duration of tolvaptan therapy is 6.78 days. Univariate and multivariate sensitivity analyses demonstrated consistent cost reduction associated with tolvaptan usage. Ten thousand cycles of Monte Carlo simulation showed the 95% CI for cost offset to be $73 to $1405.

CONCLUSION

Based on the SALT-1 and SALT-2 trials, tolvaptan usage is associated with a shorter hospital LOS than placebo among patients with the SIADH. Including the drug cost for 4 days of inpatient tolvaptan therapy, tolvaptan is associated with an estimated mean hospital cost reduction of $694 per admission in the United States.

Syndrome of inappropriate antidiuretic hormone secretion concurrent with liver disease in a dog

A 5-year-old female Chihuahua was presented for acute collapse. Laboratory examinations showed markedly elevated levels of hepatobiliary enzymes. Empiric antibiotic therapy for bacterial infection of the liver was ineffective. The clinical signs worsened with the development of hyponatremia with hypoosmolality and elevated urine sodium levels. The dog was suspected of having acute cholangiohepatitis associated with an immune-mediated disease. Subsequently, it was diagnosed with syndrome of inappropriate antidiuretic hormone secretion (SIADH) on the basis of the specific disease criteria. Further tests showed normal function of the adrenal and thyroid glands, and MRI and cerebrospinal fluid (CSF) analysis did not show any intracranial diseases. Immunosuppressive therapy and water restriction resolved the clinical signs and improved the SIADH in this dog. This case indicates that SIADH can occur concurrently with suspected immune-mediated liver disease in dogs.