Severe Hyponatremia with High Urine Sodium and Osmolality

Trimethoprim-sulfamethoxazole-induced hyponatremia in an elderly lady with Achromobacter xylosoxidans pneumonia: Case report and insights into mechanism

RATIONALE

Hyponatremia occurs frequently in the hospital setting and may be attributable to a host of etiologies. Drugs are frequently implicated. Trimethoprim-sulfamethoxazole (TMP/SMX) represents a well-recognized pharmacologic precipitant of drug-induced hyponatremia, with several reports extant in the retrievable literature. Nephrologists thus debate the mechanisms giving rise to TMP/SMX-induced hyponatremia and the precise mechanism by which treatment with TMP/SMX generates reductions of serum sodium concentration remain controversial. The agent has a well-known effect of antagonizing the effects of aldosterone upon the distal nephron. Renal salt wasting and the syndrome of inappropriate antidiuretic hormone secretion represent implicated mechanistic intermediaries in TMP/SMX-induced hyponatremia.

PATIENT CONCERNS

The patient endorsed no explicit concerns.

DIAGNOSES

We describe the case of an 83-year-old female clinically diagnosed with pneumonia found to have an initial serum sodium in the range of 130 to 134 mEq/L consistent with mild hyponatremia upon admission. Sputum cultures grew Achromobacter xylosoxidans susceptible to TMP/SMX. The patient's serum sodium concentration precipitously decline following institution of treatment with TMP/SMX to 112 to 114 mEq/L during the course of 5 days.

INTERVENTIONS

Severe hyponatremia proved recalcitrant to initial therapy with supplemental salt tabs and standard doses of the vasopressin receptor antagonist tolvaptan.

OUTCOMES

Escalating doses of tolvaptan increased the patient's sodium to 120 to 124 mEq/L. The patient was transferred to another hospital for further management. During her stay, the patient did not exhibit frank or obvious clinical features consistent with hyponatremia nor readily appreciable evidence of volume depletion.

LESSONS

TMP/SMX represents a frequent, though underreported cause of hyponatremia in the hospital setting several authors believe natriuresis may represent the most common mechanism underlying TMP/SMX-induced hyponatremia. Evidence implicating natriuresis to be mechanistic in TMP/SMX-induced hyponatremia include clinically appreciable hypovolemia and resolution of hyponatremia with oral or intravenous salt repletion. Salt repletion failed to monotherapeutically enhance our patient's hyponatremiadisfavoring renal salt wasting as originately mechanistic. Contemporaneous refractoriness of serum sodium to fluid restriction nor standard doses of tolvaptan confounded our initial attempts to mechanistically attribute the patient's hyponatremia to a specific cause. Clinical euvolemia and rapid response of hyponatremia to exceptionally high doses of tolvaptan strongly favors syndrome of inappropriate antidiuretic hormone to represent the chief mechanism by which TMP/SMX exacerbates hyponatremia.

Severe hyponatremia after donor nephrectomy

Living kidney donation is safe and established but can lead to short- and long-term complications. Hyponatremia is the most common disorder of body fluid and electrolyte balance in clinical practice, associated with increased morbidity, mortality, and the length of hospital stay. A correct diagnosis of the etiology of hyponatremia is critical, both to determine correct management and prognosis. Here, we present a case of a severe hyponatremia following left- sided donor nephrectomy with a physical examination suggestive of mild hypovolemia. Laboratory tests revealed high urine osmolality and sodium concentration mimicking syndrome of inappropriate antidiuretic hormone secretion (SIADH), in the setting of abnormally blunted response to Synacthen. The patient responded well to hydrocortisone replacement. Differentiating between primary adrenal insufficiency and SIADH as a cause of severe hyponatremia was the key to successfully treating this patient. Hyponatremia following donor nephrectomy is unusual and could be explained in this case by hypocortisolism.

Diagnosis and Treatment of Hyponatremia: Compilation of the Guidelines

Hyponatremia is a common water balance disorder that often poses a diagnostic or therapeutic challenge. Therefore, guidelines were developed by professional organizations, one from within the United States (2013) and one from within Europe (2014). This review discusses the diagnosis and treatment of hyponatremia, comparing the two guidelines and highlighting recent developments. Diagnostically, the initial step is to differentiate hypotonic from nonhypotonic hyponatremia. Hypotonic hyponatremia is further differentiated on the basis of urine osmolality, urine sodium level, and volume status. Recently identified parameters, including fractional uric acid excretion and plasma copeptin concentration, may further improve the diagnostic approach. The treatment for hyponatremia is chosen on the basis of duration and symptoms. For acute or severely symptomatic hyponatremia, both guidelines adopted the approach of giving a bolus of hypertonic saline. Although fluid restriction remains the first-line treatment for most forms of chronic hyponatremia, therapy to increase renal free water excretion is often necessary. Vasopressin receptor antagonists, urea, and loop diuretics serve this purpose, but received different recommendations in the two guidelines. Such discrepancies may relate to different interpretations of the limited evidence or differences in guideline methodology. Nevertheless, the development of guidelines has been important in advancing this evolving field.

Clinical practice guideline on diagnosis and treatment of hyponatraemia

Hyponatraemia, defined as a serum sodium concentration <135 mmol/l, is the most common disorder of body fluid and electrolyte balance encountered in clinical practice. It can lead to a wide spectrum of clinical symptoms, from subtle to severe or even life threatening, and is associated with increased mortality, morbidity and length of hospital stay in patients presenting with a range of conditions. Despite this, the management of patients remains problematic. The prevalence of hyponatraemia in widely different conditions and the fact that hyponatraemia is managed by clinicians with a broad variety of backgrounds have fostered diverse institution- and speciality-based approaches to diagnosis and treatment. To obtain a common and holistic view, the European Society of Intensive Care Medicine (ESICM), the European Society of Endocrinology (ESE) and the European Renal Association - European Dialysis and Transplant Association (ERA-EDTA), represented by European Renal Best Practice (ERBP), have developed the Clinical Practice Guideline on the diagnostic approach and treatment of hyponatraemia as a joint venture of three societies representing specialists with a natural interest in hyponatraemia. In addition to a rigorous approach to methodology and evaluation, we were keen to ensure that the document focused on patient-important outcomes and included utility for clinicians involved in everyday practice.

Clinical practice guideline on diagnosis and treatment of hyponatraemia

Hyponatraemia, defined as a serum sodium concentration <135 mmol/l, is the most common disorder of body fluid and electrolyte balance encountered in clinical practice. It can lead to a wide spectrum of clinical symptoms, from subtle to severe or even life threatening, and is associated with increased mortality, morbidity and length of hospital stay in patients presenting with a range of conditions. Despite this, the management of patients remains problematic. The prevalence of hyponatraemia in widely different conditions and the fact that hyponatraemia is managed by clinicians with a broad variety of backgrounds have fostered diverse institution- and speciality-based approaches to diagnosis and treatment. To obtain a common and holistic view, the European Society of Intensive Care Medicine (ESICM), the European Society of Endocrinology (ESE) and the European Renal Association - European Dialysis and Transplant Association (ERA-EDTA), represented by European Renal Best Practice (ERBP), have developed the Clinical Practice Guideline on the diagnostic approach and treatment of hyponatraemia as a joint venture of three societies representing specialists with a natural interest in hyponatraemia. In addition to a rigorous approach to methodology and evaluation, we were keen to ensure that the document focused on patient-important outcomes and included utility for clinicians involved in everyday practice.

Trimethoprim-associated hyponatremia

Hyponatremia associated with diuretic use can be clinically difficult to differentiate from the syndrome of inappropriate antidiuretic hormone secretion (SIADH). We report a case of a 28-year-old man with HIV (human immunodeficiency virus) and Pneumocystis pneumonia who developed hyponatremia while receiving trimethoprim-sulfamethoxazole (TMP/SMX). Serum sodium level on admission was 135 mEq/L (with a history of hyponatremia) and decreased to 117 mEq/L by day 7 of TMP/SMX treatment. In the setting of suspected euvolemia and Pneumocystis pneumonia, he was treated initially for SIADH with fluid restriction and tolvaptan without improvement in serum sodium level. A diagnosis of hyponatremia secondary to the diuretic effect of TMP subsequently was confirmed, with clinical hypovolemia and high renin, aldosterone, and urinary sodium levels. Subsequent therapy with sodium chloride stabilized serum sodium levels in the 126- to 129-mEq/L range. After discontinuation of TMP/SMX treatment, serum sodium, renin, and aldosterone levels normalized. TMP/SMX-related hyponatremia likely is underdiagnosed and often mistaken for SIADH. It should be considered for patients on high-dose TMP/SMX treatment and can be differentiated from SIADH by clinical hypovolemia (confirmed by high renin and aldosterone levels). TMP-associated hyponatremia can be treated with sodium supplementation to offset ongoing urinary losses if the TMP/SMX therapy cannot be discontinued. In this Acid-Base and Electrolyte Teaching Case, a less common cause of hyponatremia is presented, and a stepwise approach to the diagnosis is illustrated.

Aldosterone-independent regulation of the epithelial Na+ channel (ENaC) by vasopressin in adrenalectomized mice

The epithelial Na(+) channel (ENaC) in the aldosterone-sensitive distal nephron (ASDN) is under negative-feedback regulation by the renin-angiotensin-aldosterone system in protection of sodium balance and blood pressure. We test here whether aldosterone is necessary and sufficient for ENaC expression and activity in the ASDN. Surprisingly, ENaC expression and activity are robust in adrenalectomized (Adx) mice. Exogenous mineralocorticoid increases ENaC activity equally well in control and Adx mice. Plasma [AVP] is significantly elevated in Adx vs. control mice. Vasopressin (AVP) stimulates ENaC. Inhibition of the V(2) AVP receptor represses ENaC activity in Adx mice. The absence of aldosterone combined with elevated AVP release compromises normal feedback regulation of ENaC in Adx mice in response to changes in sodium intake. These results demonstrate that aldosterone is sufficient but not necessary for ENaC activity in the ASDN. Aldosterone-independent stimulation by AVP shifts the role of ENaC in the ASDN from protecting Na(+) balance to promoting water reabsorption. This stimulation of ENaC likely contributes to the hyponatremia of adrenal insufficiency.

Rhabdomyolysis in acute primary adrenal insufficiency complicated by severe hyponatraemia

Patients with acute adrenal insufficiency may have musculoskeletal symptoms including flexion contractures, myopathy and hyperkalaemic neuromyopathy. However, the association between rhabdomyolysis and acute adrenal insufficiency is extremely rare and has only been reported infrequently in the literature. Hyponatraemia is often present in association with acute adrenal insufficiency complicated by rhabdomyolysis. We herein report the case of a patient with acute primary adrenal insufficiency and severe hyponatraemia complicated by rhabdomyolysis and acute kidney injury.

Extreme hyponatraemia with intact neurological outcome in a young child with Addison's disease

The authors present the case of a 6-year-old boy with a good neurological outcome from extreme hyponatraemia caused by autoimmune hypoadrenalism. He presented with 1 week of reduced appetite, lethargy, vomiting and one episode of diarrhoea. He was described as being slightly unsteady on his feet. Clinically he was alert, although intermittently confused, with dry mucous membranes and sunken eyes. Serum sodium was 96 mmol/l with normal serum potassium and renal function. He was initially treated with 3% saline intravenously, and his serum sodium increased to 128 mmol/l by day 3. He developed slurred speech and ataxia on day 4, although MRI brain showed no evidence of pontine myelinosis, and the symptoms resolved over 1 week. A Synacthen test on day 10 confirmed a diagnosis of Addison's disease and he was commenced on hydrocortisone and fludrocortisone replacement therapy. At 5 months follow-up there are no obvious neurological or developmental sequelae.

Endocrine disorders: causes of hyponatremia not to neglect

Hyponatremia is a common electrolyte abnormality with the potential for significant morbidity and mortality. Endocrine disorders, including adrenal deficiency and hypothyroidism, are uncommon causes of hyponatremia. Primary adrenal insufficiency (i.e. Addison's disease) may well be recognized by clear hall-marks of the disease, such as pigmentation, salt craving, hypotension, and concomitant hyperkalemia. Addison's disease is an important diagnosis not to be missed since the consequences can be grave. On the other hand, hypothyroidism and secondary adrenocortical insufficiency originating from diseases of the hypothalamus and/or pituitary (hypopituitarism) require a high index of suspicion, because the clinical signs can be quite subtle. This review focuses on clinical and pathophysiological aspects of hyponatremia due to endocrine disorders.

Vasopressin-receptor antagonists

Despite a crucial role in body fluid homeostasis, elevated vasopressin levels can also be pathological in conditions such as congestive heart failure, liver cirrhosis and the syndrome of inappropriate antidiuretic hormone secretion. The result of elevated vasopressin is renal water retention and hyponatremia, a low serum sodium concentration. Hyponatremia is associated with excess morbidity and mortality. Nonpeptide vasopressin-receptor antagonists represent a new drug class of small molecules that competitively inhibit one or more of the vasopressin receptors. There are three vasopressin receptors in humans, including V1a, V1b and V2. Selective V2- and combined V1a/V2-receptor antagonists have been developed for the treatment of hyponatremia resulting from congestive heart failure, liver cirrhosis and the syndrome of inappropriate antidiuretic hormone secretion. Two nonpeptide vasopressin-receptor antagonists, conivaptan and tolvaptan, have recently been approved by American and European drug authorities for clinical use. This article aims to provide a succinct and clinical update on nonpeptide vasopressin-receptor antagonists, including their mechanism of action, performance in randomized clinical trials and current clinical status.

SIADH and hyponatraemia: why does it matter?

The vasopressin-receptor antagonists have received approval for the treatment of hyponatraemia secondary to the syndrome of inappropriate antidiuretic hormone secretion (SIADH). It is therefore necessary that physicians encountering hyponatraemia focus on SIADH. Recent studies show that hyponatraemia is often poorly managed—insufficient diagnostic tests are ordered and patients are undertreated. At the same time, it has become clear that chronic hyponatraemia causes neurological symptoms such as gait disturbances and attention deficits. However, physicians often tolerate chronic hyponatraemia as if it were benign, or as if its treatment would cause significant morbidity. Therefore, physicians must reconsider the diagnostic and therapeutic approaches to hyponatraemia and SIADH.