Tissue Glucocorticoid Metabolism in Adrenal Insufficiency: A Prospective Study of Dual-release Hydrocortisone Therapy.

BACKGROUND: Patients with adrenal insufficiency (AI) require life-long glucocorticoid (GC) replacement therapy. Within tissues, cortisol (F) availability is under the control of the isozymes of 11ß-hydroxysteroid dehydrogenase (11ß-HSD). We hypothesize that corticosteroid metabolism is altered in patients with AI because of the nonphysiological pattern of current immediate release hydrocortisone (IR-HC) replacement therapy. The use of a once-daily dual-release hydrocortisone (DR-HC) preparation, (Plenadren®), offers a more physiological cortisol profile and may alter corticosteroid metabolism in vivo. STUDY DESIGN AND METHODS: Prospective crossover study assessing the impact of 12 weeks of DR-HC on systemic GC metabolism (urinary steroid metabolome profiling), cortisol activation in the liver (cortisone acetate challenge test), and subcutaneous adipose tissue (microdialysis, biopsy for gene expression analysis) in 51 patients with AI (primary and secondary) in comparison to IR-HC treatment and age- and BMI-matched controls. RESULTS: Patients with AI receiving IR-HC had a higher median 24-hour urinary excretion of cortisol compared with healthy controls (72.1 µg/24 hours [IQR 43.6-124.2] vs 51.9 µg/24 hours [35.5-72.3], P = .02), with lower global activity of 11ß-HSD2 and higher 5-alpha reductase activity. Following the switch from IR-HC to DR-HC therapy, there was a significant reduction in urinary cortisol and total GC metabolite excretion, which was most significant in the evening. There was an increase in 11ß-HSD2 activity. Hepatic 11ß-HSD1 activity was not significantly altered after switching to DR-HC, but there was a significant reduction in the expression and activity of 11ß-HSD1 in subcutaneous adipose tissue. CONCLUSION: Using comprehensive in vivo techniques, we have demonstrated abnormalities in corticosteroid metabolism in patients with primary and secondary AI receiving IR-HC. This dysregulation of pre-receptor glucocorticoid metabolism results in enhanced glucocorticoid activation in adipose tissue, which was ameliorated by treatment with DR-HC.

Treatment Guidelines for Hyponatremia: Stay the Course.

International guidelines designed to minimize the risk of complications that can occur when correcting severe hyponatremia have been widely accepted for a decade. On the basis of the results of a recent large retrospective study of patients hospitalized with hyponatremia, it has been suggested that hyponatremia guidelines have gone too far in limiting the rate of rise of the serum sodium concentration; the need for therapeutic caution and frequent monitoring of the serum sodium concentration has been questioned. These assertions are reminiscent of a controversy that began many years ago. After reviewing the history of that controversy, the evidence supporting the guidelines, and the validity of data challenging them, we conclude that current safeguards should not be abandoned. To do so would be akin to discarding your umbrella because you remained dry in a rainstorm. The authors of this review, who represent 20 medical centers in nine countries, have all contributed significantly to the literature on the subject. We urge clinicians to continue to treat severe hyponatremia cautiously and to wait for better evidence before adopting less stringent therapeutic limits.

Adrenal insufficiency is common amongst kidney transplant recipients receiving maintenance prednisolone and can be predicted using morning cortisol.

BACKGROUND: Long-term glucocorticoid therapy is a key component of immunosuppression for kidney transplant recipients (KTRs), leading to significant cumulative glucocorticoid exposure. The aims of this study are to investigate the prevalence of adrenal insufficiency (AI) in KTRs taking prednisolone and to develop a screening algorithm to identify patients at the highest risk of AI. METHODS: In this cross-sectional cohort study, 67 KTRs receiving prednisolone underwent a short synacthen test (SST) and measurement of cumulative glucocorticoid exposure. RESULTS: A total of 72% (n = 48) of participants failed the SST. Participants with AI had a higher daily prednisolone dose (4.9 versus 4.2 mg/day; P = .002) and greater cumulative glucocorticoid exposure (289 versus 111 mg/kg; P = .03) than those with intact adrenal function. Participants with AI had lower baseline cortisol than participants with intact adrenal function (143 versus 303 nmol/L; P < .001). Morning cortisol of >288 nmol/L predicted a normal SST with 100% specificity [95% confidence interval (CI) 92-100] and 70% sensitivity (95% CI 56-78%), therefore excluding AI. CONCLUSIONS: Our results suggest KTRs are at a higher risk for AI than previously reported. A morning serum cortisol measurement is a useful screening tool in this cohort, reducing the need for stimulatory testing by 44%. KTRs with AI need education regarding glucocorticoid sick rules, similar to patients with other forms of AI.

The Contribution of Oral and Inhaled Glucocorticoids to Adrenal Insufficiency in Asthma.

BACKGROUND: Exposure to any form of glucocorticoid preparation is associated with a risk of adrenal insufficiency (AI). OBJECTIVE: To establish the contribution of oral corticosteroid (OCS) and inhaled corticosteroid (ICS) exposure to the risk of AI in a cohort of patients (n = 80) with severe, uncontrolled asthma. METHODS: We compiled individualized cumulative OCS and ICS exposure data using a combination of health care records and electronic inhaler monitoring using an Inhaler Compliance Assessment device and estimated the risk of AI for each participant using a morning serum cortisol concentration. RESULTS: The predicted prevalence of AI based on morning cortisol concentrations was 25% (20 of 80). Participants on maintenance OCS therapy had the highest risk of AI at 60% (6 of 10) compared with 17% (11 of 65) in those with no recent OCS exposure. Morning serum cortisol correlated negatively with both OCS exposure (mg/kg prednisolone) (r = -0.4; P < .0002) and ICS exposure (mg/kg fluticasone propionate) (r = -0.26; P = .019). Logistic regression of risk of AI against the number of standard treatment courses of OCS demonstrated a positive relationship although this did not reach statistical significance (odds ratio, 1.41; 95% CI, 0.97-2.05; P = .073). Logistic regression analysis, categorizing patients as high-risk AI (cortisol <130 nmol/L) or not (cortisol >130 nmol/L), showed that cumulative ICS exposure remained a significant predictor of AI, even when exposure to OCS was controlled for (odds ratio, 2.17 per 1 mg/kg increase in cumulative fluticasone propionate exposure; 95% CI, 1.06-4.42; P = .033). CONCLUSIONS: Our data suggest that AI is common among patients with asthma and highlights that the risk of AI is associated with both high-dose ICS therapy and intermittent treatment courses of OCS.

Diagnosis and Management of Central Diabetes Insipidus in Adults.

Central diabetes insipidus (CDI) is a clinical syndrome which results from loss or impaired function of vasopressinergic neurons in the hypothalamus/posterior pituitary, resulting in impaired synthesis and/or secretion of arginine vasopressin (AVP). AVP deficiency leads to the inability to concentrate urine and excessive renal water losses, resulting in a clinical syndrome of hypotonic polyuria with compensatory thirst. CDI is caused by diverse etiologies, although it typically develops due to neoplastic, traumatic, or autoimmune destruction of AVP-synthesizing/secreting neurons. This review focuses on the diagnosis and management of CDI, providing insights into the physiological disturbances underpinning the syndrome. Recent developments in diagnostic techniques, particularly the development of the copeptin assay, have improved accuracy and acceptability of the diagnostic approach to the hypotonic polyuria syndrome. We discuss the management of CDI with particular emphasis on management of fluid intake and pharmacological replacement of AVP. Specific clinical syndromes such as adipsic diabetes insipidus and diabetes insipidus in pregnancy as well as management of the perioperative patient with diabetes insipidus are also discussed.

Approach to the Patient: Hyponatremia and the Syndrome of Inappropriate Antidiuresis (SIAD).

Hyponatremia is the most common electrolyte disturbance seen in clinical practice, affecting up to 30% of acute hospital admissions, and is associated with significant adverse clinical outcomes. Acute or severe symptomatic hyponatremia carries a high risk of neurological morbidity and mortality. In contrast, chronic hyponatremia is associated with significant morbidity including increased risk of falls, osteoporosis, fractures, gait instability, and cognitive decline; prolonged hospital admissions; and etiology-specific increase in mortality. In this Approach to the Patient, we review and compare the current recommendations, guidelines, and literature for diagnosis and treatment options for both acute and chronic hyponatremia, illustrated by 2 case studies. Particular focus is concentrated on the diagnosis and management of the syndrome of inappropriate antidiuresis. An understanding of the pathophysiology of hyponatremia, along with a synthesis of the duration of hyponatremia, biochemical severity, symptomatology, and blood volume status, forms the structure to guide the appropriate and timely management of hyponatremia. We present 2 illustrative cases that represent common presentations with hyponatremia and discuss the approach to management of these and other causes of hyponatremia.

Is repeat fine needle aspiration required in thyroid nodules with initial benign cytology? Results from a large Irish series.

BACKGROUND : Fine needle aspiration (FNA) cytology is the preferred method for assessing thyroid nodules for malignancy. Concern remains about the rate of false negative results. The primary aim of this study is to investigate the malignancy rate of thyroid nodules initially classified as benign (Thy 2). METHODS: We retrospectively examined 658 nodules in 653 (429 female) patients between January 2013 to December 2017. All FNA biopsies (FNABs) were performed under ultrasound (US) guidance by a radiologist with expertise in thyroid pathology. Nodules were cytologically classified according to the UK Royal College of Pathologists guidelines. Decisions about further management were made at a regular thyroid multidisciplinary meeting. Follow up of the Thy 2 nodules was determined based on clinical and radiological criteria. RESULTS: The mean age (± SD) was 53.2 (14.6) years. Five hundred out of 658 (76.0%) nodules were classified as Thy 2 (benign) after the first FNAB. Of these thyroid nodules initially classified as benign, 208 (41.6%) underwent repeat FNAB and 9 (1.8%) were surgically removed without repeat FNAB. The remainder were followed up clinically and/or radiologically. Seven (1.4%) of nodules initially classified as Thy 2 were later shown to be or to harbor malignancy after a follow-up of 74.5 (± 19.7) months. Papillary thyroid microcarcinomas were found co-incidentally in two thyroid glands of benign nodules, giving a true prevalence of 5/500 (1.0%). CONCLUSIONS: With a well targeted FNAB, the false negative rate of an initial benign thyroid FNA is very low thus routine second FNAB is not required in patients with a thyroid nodule initially deemed benign. Multidisciplinary input is imperative in informing decision making.

Understanding the Presence of Mental Fatigue in Elite Female Football.

Purpose: Previous research investigating the impact of induced mental fatigue in football (soccer) has demonstrated associated performance decrements in physical, technical, tactical and decision-making performance. A common limitation amongst this research is the protocols used to induce mental fatigue which provides low ecological validity, and the inclusion of recreational or sub-elite players. Therefore, understanding the presence of mental fatigue in elite football can provide insight into protocols with greater ecological validity. Methods: The current study used focus groups with 10 elite female football players, focusing on five topics (travel, fixture congestion, receiving tactical information, pre-match routine and pressure to win) related to the perceived causes of mental fatigue in elite football (directed by anecdotal quotes in elite football and research-based theories). Results: Several themes emerged from the data; travel fatigue, inability to switch off from football, fatigue experienced following team meetings, use of pre-match music and internal pressure to succeed. Conclusion: These findings present practical recommendations to reduce mental fatigue in elite football settings, such as considering the timing, content and duration of team meetings, providing players with free time/rest where possible, and considering the modality of coaching instructions during matches.

ENDOCRINOLOGY IN THE TIME OF COVID-19-2021 UPDATES: The management of diabetes insipidus and hyponatraemia.

COVID-19 has changed the nature of medical consultations, emphasizing virtual patient counselling, with relevance for patients with diabetes insipidus (DI) or hyponatraemia. The main complication of desmopressin treatment in DI is dilutional hyponatraemia. Since plasma sodium monitoring is not always possible in times of COVID-19, we recommend to delay the desmopressin dose once a week until aquaresis occurs allowing excess retained water to be excreted. Patients should measure their body weight daily. Patients with DI admitted to the hospital with COVID-19 have a high risk for mortality due to volume depletion. Specialists must supervise fluid replacement and dosing of desmopressin. Patients after pituitary surgery should drink to thirst and measure their body weight daily to early recognize the development of postoperative SIAD. They should know hyponatraemia symptoms. Hyponatraemia in COVID-19 is common with a prevalence of 20-30% and is mostly due to SIAD or hypovolaemia. It mirrors disease severity and is an early predictor of mortality. Hypernatraemia may also develop in COVID-19 patients, with a prevalence of 3-5%, especially in ICU, and derives from different multifactorial reasons, for example, due to insensible water losses from pyrexia, increased respiration rate and use of diuretics. Hypernatraemic dehydration may contribute to the high risk of acute kidney injury in COVID-19. IV fluid replacement should be administered with caution in severe cases of COVID-19 because of the risk of pulmonary oedema.

Cardiometabolic and psychological effects of dual-release hydrocortisone: a cross-over study.

BACKGROUND: Adrenal insufficiency (AI) is associated with increased cardiovascular morbidity and mortality and reduced quality of life (QoL). Optimum glucocorticoid (GC) dosing and timing are crucial in the treatment of AI, yet the natural circadian secretion of cortisol is difficult to mimic. The once-daily dual-release hydrocortisone (DR-HC) preparation (Plenadren®), offers a more physiological cortisol profile and may address unmet needs. METHODS: An investigator-initiated, prospective, cross-over study in patients with AI. Following baseline assessment of cardiometabolic risk factors and QoL, patients switched from their usual hydrocortisone regimen to a once-daily dose equivalent of DR-HC and were reassessed after 12 weeks of treatment. RESULTS: Fifty-one patients (21 PAI/30 SAI) completed the study. Mean age was 41.6 years (s.d. 13), and 58% (n = 30) were male. The median daily HC dose before study entry was 20 mg (IQR 15-20 mg). After 3 months on DR-HC, the mean SBP decreased by 5.7 mmHg, P = 0.0019 and DBP decreased by 4.5 mmHg, P = 0.0011. There was also a significant reduction in mean body weight (-1.23 kg, P = 0.006) and BMI (-0.3 kg/m2, P = 0.003). In a sub-analysis, there was a greater reduction in SBP observed in patients with SAI when compared to PAI post-DR-HC. Patients reported significant improvements in QoL using three validated QoL questionnaires, with a greater improvement in PAI. CONCLUSION: Dual-release hydrocortisone decreases BP, weight and BMI compared with conventional HC treatment, even at physiological GC replacement doses. Additionally, DR-HC confers significant improvements in QoL compared to immediate-release HC, particularly in patients with PAI, which is also reflected in the patient preference for DR-HC.

Active management of hyponatraemia and mortality in older hospitalised patients compared with younger patients: results of a prospective cohort study.

INTRODUCTION: Hyponatraemia is associated with increased morbidity and mortality; the aetiology and outcomes of hyponatraemia in older patients have not been defined in prospective studies. METHODS: A single-centre 9-month prospective observational study in which clinical outcomes in hospitalised patients ≥ 65 years (older patients with hyponatraemia (OP-HN)) and those <65 years (young patients with hyponatraemia (YP-HN)) with hyponatraemia were analysed, and compared with eunatraemic controls (older patients with normonatraemia (OP-NN) and young patients with normonatraemia (YP-NN)). RESULTS: In total, 1,321 episodes of hyponatraemia in 1,086 patients were included; 437 YP-HN, median age 54 years (IQR 44,60) and 884 OP-HN, median age 77 years (IQR 71,82). A total of 1,120 consecutive eunatraemic control patients were simultaneously recruited; 690 OP-NN, median age 77 years (IQR 71,83) and 430 YP-NN, median age 52 years (IQR 41,58). Euvolaemic hyponatraemia was the commonest cause of hyponatraemia in both age groups (48% in YP-HN and 46% in OP-HN). Sixty-two percent of OP-HN received hyponatraemia-directed treatment within the initial 48 h, compared with 55% of YP-HN, P = 0.01. Despite the greater treatment rates in OP-HN, younger patients were 24% more likely to be discharged with normal plasma sodium concentration (pNa) compared with older patients, relative risk (RR) 1.24 (95% confidence interval (CI) 1.12-1.37), P < 0.001.Using OP-NN as the reference group, the RR of in-hospital death in OP-HN was 2.15 (95% CI 1.3-3.56), P = 0.002. Using YP-NN as the reference group, the RR of in-hospital death in YP-HN was 4.34 (95% CI 1.98-9.56), P < 0.001. CONCLUSION: Despite greater rates of HN-targeted treatment, the risk of in-hospital death is increased in older hyponatraemic patients compared with older eunatraemic controls. The impact of hyponatraemia on mortality is even greater in younger patients.

Active management of severe hyponatraemia is associated with improved mortality.

OBJECTIVE: Severe hyponatraemia (plasma sodium concentration, pNa <120 mmol/L) is reported to be associated with mortality rates as high as 50%. Although there are several international guidelines for the management of severe hyponatraemia, there are few data on the impact of treatment. DESIGN AND METHODS: We have longitudinally reviewed rates of specialist input, active management of hyponatraemia, treatment outcomes and mortality rates in patients with severe hyponatraemia (pNa <120 mmol/L) in 2005, 2010 and 2015, and compared the recent mortality rate with that of patients with pNa 120-125 mmol/L. RESULTS: Between 2005 and 2010 there was a doubling in the rate of specialist referral (32 to 68%, P = 0.003) and an increase in the use of active management of hyponatraemia in patients with pNa <120 mmol/L (63 to 88%, P = 0.02), associated with a reduction in mortality from 51 to 15% (P < 0.001). The improved rates of intervention were maintained between 2010 and 2015, but there was no further reduction in mortality. When data from all three reviews were pooled, specialist consultation in patients with pNa <120 mmol/L was associated with a 91% reduction in mortality risk, RR 0.09 (95% CI: 0.03-0.26), P < 0.001. Log-rank testing on in-hospital survival in 2015 found no significant difference between patients with pNa <120 mmol/L and pNa 120-125 mmol/L (P = 0.56). CONCLUSION: Dedicated specialist input and active management of severe hyponatraemia are associated with a reduction in mortality, to rates comparable with moderate hyponatraemia.

Fluid Restriction Therapy for Chronic SIAD; Results of a Prospective Randomized Controlled Trial.

CONTEXT: Fluid restriction (FR) is the recommended first-line treatment for syndrome of inappropriate antidiuresis (SIAD), despite the lack of prospective data to support its efficacy. DESIGN: A prospective nonblinded randomized controlled trial of FR versus no treatment in chronic SIAD. INTERVENTIONS AND OUTCOME: A total of 46 patients with chronic asymptomatic SIAD were randomized to either FR (1 liter/day) or no specific hyponatremia treatment (NoTx) for 1 month. The primary endpoints were change in plasma sodium concentration (pNa) at days 4 and 30. RESULTS: Median baseline pNa was similar in the 2 groups [127 mmol/L (interquartile range [IQR] 126-129) FR and 128 mmol/L (IQR 126-129) NoTx, P = 0.36]. PNa rose by 3 mmol/L (IQR 2-4) after 3 days FR, compared with 1 mmol/L (IQR 0-3) NoTx, P = 0.005. There was minimal additional rise in pNa by day 30; median pNa increased from baseline by 4 mmol/L (IQR 2-6) in FR, compared with 1 mmol/L (IQR 0-1) NoTx, P = 0.04. After 3 days, 17% of FR had a rise in pNa of ≥5 mmol/L, compared with 4% NoTx, RR 4.0 (95% CI 0.66-25.69), P = 0.35. After 3 days, 61% of FR corrected pNa to ≥130 mmol/L, compared with 39% of NoTx, RR 1.56 (95% CI 0.87-2.94), P = 0.24. CONCLUSION: FR induces a modest early rise in pNa in patients with chronic SIAD, with minimal additional rise thereafter, and it is well-tolerated. More than one-third of patients fail to reach a pNa ≥130 mmol/L after 3 days of FR, emphasizing the clinical need for additional therapies for SIAD in some patients.

ENDOCRINOLOGY IN THE TIME OF COVID-19: Management of diabetes insipidus and hyponatraemia.

COVID-19 has changed the nature of medical consultations, emphasizing virtual patient counseling, with relevance for patients with diabetes insipidus (DI) or hyponatraemia. The main complication of desmopressin treatment in DI is dilutional hyponatraemia. Since plasma sodium monitoring is not always possible in times of COVID-19, we recommend to delay the desmopressin dose once a week until aquaresis occurs allowing excess retained water to be excreted. Patients should measure their body weight daily. Patients with DI admitted to the hospital with COVID-19 have a high risk for mortality due to volume depletion. Specialists must supervise fluid replacement and dosing of desmopressin. Patients after pituitary surgery should drink to thirst and measure their body weight daily to early recognize the development of the postoperative syndrome of inappropriate antidiuresis (SIAD). They should know hyponatraemia symptoms. The prevalence of hyponatraemia in patients with pneumonia due to COVID-19 is not yet known, but seems to be low. In contrast, hypernatraemia may develop in COVID-19 patients in ICU, from different multifactorial reasons, for example, due to insensible water losses from pyrexia, increased respiration rate and use of diuretics. Hypernatraemic dehydration may contribute to the high risk of acute kidney injury in COVID-19. IV fluid replacement should be administered with caution in severe cases of COVID-19 because of the risk of pulmonary oedema.

Understanding the presence of mental fatigue in English academy soccer players.

Research has demonstrated that induced mental fatigue impairs soccer-specific technical, tactical and physical performance in soccer players. The findings are limited by the lack of elite players and low ecological validity of the tasks used to induce mental fatigue, which do not resemble the cognitive demands of soccer. The current study collected survey data from English academy soccer players (n = 256; age groups - U14 - U23), with questions comprising of five themes (descriptors of physical and mental fatigue, travel, education, match-play and fixture congestion). The survey consisted of multiple choice responses, checkboxes and blinded/unblinded (for duration based questions) 0-100 arbitrary unit (AU) slider scales. Listening to music (81.6% of players), using social media (58.3%) and watching videos (34.3%) were the most common pre-match activities. Pre-match subjective mental fatigue was low (18.7±18.8 AU), and most frequently reported at the end of a match (47±26 AU) and remained elevated 24-hours post-match (36±27 AU). Travel (29±24 AU), fixture congestion (44±25 AU) and education (30±26 AU) demonstrated a low to moderate presence of subjective mental fatigue. These findings provide an overview of activities performed by English academy soccer players pre-match, and demonstrate that mental fatigue is experienced as a result of match-play.

Continuous Versus Bolus Infusion of Hypertonic Saline in the Treatment of Symptomatic Hyponatremia Caused by SIAD.

BACKGROUND: Acute hyponatremia is a medical emergency that confers high mortality, attributed primarily to cerebral edema. Expert guidelines advocate the use of intravenous boluses of hypertonic saline rather than traditional continuous infusion to achieve a faster initial rise in plasma sodium (pNa) concentration. However, there is a limited evidence base for this recommended policy change. METHODS: We prospectively assessed the clinical and biochemical outcomes in patients treated for symptomatic hyponatremia caused by syndrome of inappropriate antidiuresis in response to intravenous bolus treatment with 3% saline (100 mL, repeated up to two more times) and compared the outcomes to retrospective data from patients treated with continuous intravenous infusion of low-dose (20 mL/h) 3% saline. RESULTS: Twenty-two patients were treated with bolus infusion and 28 with continuous infusion. Three percent saline bolus caused more rapid elevation of pNa at 6 hours [median (range) 6 (2 to11) vs 3 (1 to 4) mmol/L, P < 0.0001], with a concomitant improvement in Glasgow Coma Scale (GCS) [median (range) 3 (1 to 6) vs 1 (-2 to 2), P < 0.0001] at 6 hours. Median pNa concentration was similar at 24 hours in the two treatment groups. The administration of a third saline bolus was associated with greater need for dextrose/dDAVP to prevent overcorrection (OR 24; P = 0.006). There were no cases of osmotic demyelination in either group. CONCLUSION: Three percent saline bolus produces faster initial elevation of pNa than continuous infusion with quicker restoration of GCS, and without osmotic demyelination. Frequent electrolyte monitoring, and judicious intervention with dDAVP is required to prevent overcorrection with bolus therapy.

Hyponatremia and Glucocorticoid Deficiency.

Hyponatremia is the commonest electrolyte deficiency in clinical practice. Of the many causes of hyponatremia, syndrome of inappropriate antidiuresis (SIAD) is the commonest. Glucocorticoid deficiency, due to central/secondary adrenal insufficiency, is the key differential diagnosis for SIAD, as it presents with a similar biochemical picture of euvolemic hyponatremia and inappropriate urinary concentration. The underlying mechanisms for the development of hyponatremia in glucocorticoid deficiency are: (1) impaired renal water handling in the absence of circulating cortisol and (2) increased plasma concentrations of arginine vasopressin (AVP), despite hypo-osmolality. The original diagnostic criteria for SIAD emphasized that normal adrenal reserve was essential for its diagnosis, in recognition of the similar biochemical presentation of SIAD and glucocorticoid deficiency. This has been emphasized in all of the recently published clinical guidelines. However, data from the literature suggest that clinicians ignore the measurement of plasma cortisol concentration in both clinical practice and research protocols. The reported prevalence of glucocorticoid deficiency in patients presenting with euvolemic hyponatremia may, therefore, be underestimated and patients with a dangerous, but treatable cause of hyponatremia are inevitably missed. In this chapter, we will review the physiopathology of hyponatremia in the setting of glucocorticoid deficiency. We will discuss the differential diagnosis of euvolemic hyponatremia and review the prevalence of glucocorticoid deficiency in patients with hyponatremia.