Approach to and management of abnormalities in plasma sodium

The differential diagnosis between hypertonic, isotonic and hypotonic hyponatremia are presented. The help of some usual serum (urea, uric acid and TCO₂) and urine parameters (mainly osmolality and sodium concentration) are discussed and help to determine the best treatment. Morbidity associated with untreated hyponatremia and with the different treatment available is also discussed. Who to prevent and treat ODS (osmotic demyelating syndrome) is recalled. The pathophysiology and treatment of hypernatremia are also discussed.

Mild water restriction with or without urea for the longterm treatment of syndrome of inappropriate antidiuretic hormone secretion (SIADH): Can urine osmolality help the choice?

BACKGROUND

Treatment options for chronic SIADH include water restriction (WR) and urea. The usefulness of urine osmolality to guide the choice of the treatment option is not clearly defined. We hypothesized that urine osmolality can indicate whether treatment with mild water restriction alone could be successful.

METHODS

Retrospective Review of clinical and biochemical (blood and urine) data of patients with chronic SIADH treated for at least one year with mild WR (1.5-2l/day) either with or without urea.

RESULTS

Twenty nine patients were included. Nine patients were treated by mild WR. Mean serum sodium (SNa) and mean Uosm were 129±2mEq/l and 274±78mOsm/kgH2O respectively before WR, and increased to 138.5±3mEq/l and 505±87mOsm/kgH₂O (P<0.001). Eight patients were treated with mild WR and 15g urea daily, the SNa and Uosm before treatment were 127.5±3mEq/l and 340±100mOsm/kgH₂O respectively and increased to 136.5±1mEq/l and 490±151mOsm/kgH₂O (P<0.001). Four of the eight patients had a permanent low solute intake which contributed to hyponatremia. Twelve patients needed 30g urea daily combined with mild WR. The SNa and Uosm were respectively 126±2mEq/l and 595±176mOsm/kgH₂O and increased to 136.5±2mEq/l and 698±157mOsm/kgH₂O (P<0.05). Uosm increased in most of the treated patients.

CONCLUSIONS

About 30% of patients could be treated by moderate WR alone. All these patients presented an initial urine osmolality lower than 400mOsm/kgH₂O.

Hyperglycemia induces attention and gait deficits in diabetic mellitus patients

AIMS

Patients with diabetes mellitus experience a large number of falls and bone fractures that are not related solely to complications of the disease. The purpose of our study was to determine whether transient hyperglycemia affects attentional functions and gait.

METHODS

This was a case-control study. We asked 17 patients with type 1 or type 2 diabetes mellitus to perform three visual tests and one visual and auditory attention test (Phasic Alert A1-4 and A2-3, Go/No Go, Intermodal Comparison). Mean response time (ms) and total number of errors were assessed. Ten of the patients also performed a tandem gait test consisting of three steps. The total distance travelled (TDT, in mm) by the center of pressure was measured with a pressure-sensitive calibrated platform. Transient hyperglycemia was defined as blood glucose level greater than 13, 8 mmol/L at the time of the test. These same patients were retested 1-3 days later at a blood glucose level at least 5, 5 mmol/L lower than the initial values (T24-72h). Nineteen patients with diabetes mellitus were matched with the original participants and performed the same test under normoglycemic conditions.

RESULTS

During transient hyperglycemia, the mean response time (ms) and the TDT were significantly longer. The mean response time for the four tests increased by 53, 5 ms (P < 0.001). There was no increase in the number of errors. The TDT of the center of pressure increased significantly by 102 mm (P < 0.001).

CONCLUSIONS

Transient hyperglycemia alters attention and gait in patients with diabetes mellitus.

Mild hyponatremia and risk of fracture in the ambulatory elderly

BACKGROUND

Mild hyponatremia is the commonest electrolyte imbalance in the older population and has been shown to be associated with gait and attention deficits resulting in higher frequency of falls. The association of mild hyponatremia and bone fracture is still unknown.

OBJECTIVE

To determine if mild hyponatremia is associated with increased risk of bone fracture in ambulatory elderly.

DESIGN, SETTING AND PARTICIPANTS

Case control study of 513 cases of bone fracture after incidental fall in ambulatory patients aged 65 or more in general university hospital. Controls were age and sex matched randomly selected ambulatory patients without history of bone fracture.

MAIN EXPOSURE MEASURES

Odds ratio (OR) of bone fracture after incidental fall associated with presence of hyponatremia.

RESULTS

Prevalence of hyponatremia (serum sodium <135 mEq/l,) in patients with bone fracture and in controls patient was, respectively, 13.06% and 3.90%. Hyponatremia was mild and asymptomatic in all patients (mean serum sodium 131 mEq/l) and was found to be associated with bone fracture after incidental fall in ambulatory elderly (unadjusted OR: 3.47, 95% CI: 2.09-5.79, and adjusted OR: 4.16 95% CI: 2.24-7.71). Hyponatremia was either drug induced (36% diuretics, 17% selective serotonin reuptake inhibitors) or resulted from idiopathic syndrome of inappropriate antidiuretic hormone secretion (37%). Hyponatremia was associated with 9.20% of all bone fractures.

CONCLUSION

Mild asymptomatic hyponatremia is associated with bone fracture in ambulatory elderly and avoiding iatrogenic hyponatremia or treating hyponatremia may decrease the number of bone fractures in this population.

Inefficacy of intravenous immunoglobulins and infliximab in Degos' disease

We report the case of a 60-year-old man who presented with sudden visual loss, a history of postprandial abdominal pain, malabsorption, and skin lesions typical of systemic Degos' disease. Despite anti-aggregants and prednisone the patient's status did not improve. On the basis of the hypothetical dysimmune origin of this disease, we attempted treatment with intravenous immunoglobulins, without success. We then administered infliximab (Remicade), but 2 months after the third injection the patient developed mesenteric infarction and died. We therefore believe that both intravenous immunoglobulins and antiTNFalpha are ineffective for the treatment of Degos' disease.

An atypical case of Whipple's disease: case report and review of the literature

We report the case of a 57-year-old man, presenting with bilateral panuveitis, bilateral sacroiliitis, intermittent pyrexia and a pulmonary nodule. The patient had been under immunosuppressive treatment for 2 years for Behçet's disease. However, he did not fulfill the diagnostic criteria of Behçet's disease. Blood analysis showed a very high C reactive protein (CRP at 34 mg/dl). In view of severe intra-ocular inflammation, the anterior chamber was punctured. Polymerase chain reaction (PCR) on the aqueous humour and on the blood revealed the presence of Tropheryma whippelii DNA, an agent responsible for Whipple's disease. The patient was treated with ceftriaxone followed by trimethoprim-sulfamethoxazol for 1 year with good clinical and biological evolution. This case illustrates the difficulty to diagnose an atypical Whipple's disease. In cases of uveitis with atypical signs and/or not responding to the treatment, the internist must consider to perform an analysis of the ocular fluids.

Myopericarditis revealing adult-onset Still's disease

We report the case of a 33 year-old man presenting with fever, arthralgias, sore throat, dyspnea and chest pain. Myopericarditis was diagnosed on the basis of electrocardiogram, echocardiography and cardiac magnetic resonance imaging (MRI). The dramatic increase in ferritinemia suggested the diagnosis of adult-onset Still's disease (AOSD), which could be established according to criteria of Yamaguchi. Rapid improvement occured under corticosteroids. Myocarditis is very rare in AOSD, pericarditis being more frequent. We report herein the first description of AOSD associated myocarditis evidenced by cardiac MRI.

Positive octreotide scintigraphy and determination of lanreotide activity in Paget's disease of bone associated with phosphate diabetes: a case report

A patient with Paget's disease developed phosphate diabetes (phosphate: 1.6 mg/dl (2.5-4.4 mg/dl), with 29 ml/min phosphate clearance (Nl<15ml/min) and a 65% phosphate reabsorption rate (Nl>85%). As previously demonstrated in tumor-induced osteomalacia, we hypothesized that osteoblasts might manifest somatostatin receptor activity. The patient underwent an octreotide scan which demonstrated increased uptake localized in affected bone. Under lanreotide treatment (40 mg i.m.), the patient's bone pain improved with a concomitant decrease in phosphate alkaline level. Phosphate clearance and tubular readsorption rate of phosphate did not change significantly. We reviewed previously reported cases of associated Paget's bone disease and phosphate diabetes.

Low plasma bicarbonate level in hyponatremia related to adrenocorticotropin deficiency

Patients with hyponatremia related to adrenocorticotropic deficiency are not easily distinguished by routine laboratory studies from patients with nonendocrine inappropriate secretion of antidiuretic hormone (SIADH). We wanted to investigate whether, in the routine biological analysis of such patients, some parameters could help to better identify this subgroup of hyponatremic patients. The biochemical profiles of 13 consecutive patients with hyponatremia related to ACTH deficiency were analyzed and compared with 30 consecutive patients with classical SIADH. Patients with adrenocorticotropic deficiency presented low uric acid and urea levels as in nonendocrine SIADH, but their total carbon dioxide was significantly lower (total CO(2), 20.5 +/- 3 vs. 25.5 +/- 2.4 mmol/liter; P < 0.001). Nine of the 13 patients presented a value lower than 22 mmol/liter, although this was not observed in the nonendocrine SIADH patients (P < 0.001). Arterial blood gas analysis was available in eight patients and showed a compensated respiratory alkalosis in most of them (pH 7.42 +/- 0.02; PCO(2), 30 +/- 5 mm Hg; HCO(3)(-), 20 +/- 2 mmol/liter; base excess, -3.4 +/- 1.8 mmol/liter). Aldosterone levels were much lower in ACTH deficiency patients during the hyponatremic state (33 +/- 40 pg/ml) when compared with the nonendocrine SIADH (120 +/- 60 pg/ml; P < 0.01). Correction of hyponatremia by cortisone therapy normalized total CO(2) and aldosterone levels. Low carbon dioxide level is a frequent observation in hyponatremia related to ACTH deficiency and could help to differentiate it from classical SIADH.

Possible association between deep infection and hypertrophic osteoarthropathy. Report of three cases and review of the literature

Hypertrophic Osteoarthropathy is classically associated with chronic pulmonary disease, cancer or inflammatory bowel disease. However, deep infection such as vascular graft infection is an etiology important to recognize because of the risk of life-threatening complication (aorto-enteric fistula). In this study, we reported two cases of aortic graft infection and one case of para-anal abscess associated with hypertrophic osteoarthropathy. The previously reported cases are reviewed.

Solute loss plays a major role in polydipsia-related hyponatraemia of both water drinkers and beer drinkers

BACKGROUND

Polydipsia-related hyponatraemia is generally considered an acute dilutional state.

AIM

To determine whether solute loss plays a role in the pathogenesis of polydipsia-related hyponatraemia.

DESIGN

Prospective uncontrolled study.

METHODS

We studied routine biochemical volume-related parameters before and after 2 l isotonic saline infusion over 24 h, in 10 consecutive hyponatraemic polydipsia patients (mean age 55 +/- 11 years; 6 beer drinkers and 4 compulsive water drinkers) with initial urinary osmolality <220 mosm/kg H(2)O. In five of these patients, we measured balance data over 24 h.

RESULTS

Mean initial plasma protein concentration in the 10 studied polydipsia patients was 7 +/- 0.7 g/dl, unexpectedly high for an acute dilutional state. Mean plasma sodium concentration increased from 126 +/- 5 mmol/l before saline, to 135 +/- 5 mmol/l after infusion of 2 l isotonic saline (p < 0.01). Balance data in five polydipsia patients showed a mean decrease of 1.6 kg of their initial body weight and a mean salt retention of 406 mosm.

DISCUSSION

Polydipsia-related hyponatraemia is a mixed disorder, in which about half of sodium decrease is due to solute loss. This explains the apparent paradox of a normal plasma protein concentration, despite the increase in body weight due to water intoxication.

[The general internal medicine department]

The Department of General Internal Medicine is devoted to the evaluation of patients with autoimmune systemic diseases, multiorganic disorders or presenting non specific symptoms such as chronic fatigue, unexplained weight loss or fever of unknown origin. The interest in salt and water metabolisms had led to original contributions in the treatment of hyponatremia in man and to the understanding of the osmotic demyelinating syndrome in a rat model of hyponatremia. The study of ageing in man and rodents had contributed to better understand lymphocyte and thyroid function in the elderly. The care for patients with various autoimmune disorders led to original observations in the pathogenicity of Sjögren's syndrome adult onset Still disease or sarcoidosis as well as the follow up of patients treated with azathioprine. Intensive collaboration with the Department of Immunology led to identify Th2 clonal lymphocytes as the cause of the so-called idiopathic hypereosinophilic syndrome in some patients and to define the clinical and biological features in this subset of patients.

[Review on hypertrophic osteoarthropathy and digital clubbing]

Clubbing was first described by Hippocrates more than 2.500 years ago. It may be seen alone or as part of an entity called hypertrophic osteoarthropathy which include periostitis, arthritis and sometimes thickening and edema of the skin around the affected joints. Pulmonary diseases such as cancer, abscess, empyema, bronchiectasis and cystic fibrosis are the major diseases known to be associate with hypertrophic osteoarthropathy. Digestive tract cancer, cyanogenic congenital heart disease are well known association. Many theories have attempted to explain the appearance of this sign but few have persisted. In this article, we review characteristics, relation with etiology and the basis of the pathophysiology of hypertrophic osteoarthropathy and particularly of clubbing.

Utility and limitations of biochemical parameters in the evaluation of hyponatremia in the elderly

We evaluated in 110 consecutive elderly hyponatremic patients the value of traditional clinical and biochemical data and the place of a test infusion of 2 liters isotonic saline over 24 hours, in establishing the etiology of the hyponatremia. The causes of hyponatremia were as follows: 31% SIADH patients, 23% patients with hyponatremia due to diuretics, 18% potomania patients, 15% salt depleted patients, 5% salt depleted SIADH patients, 5% patients with a salt loosing syndrome and 3% patients with hyponatremia of unknown origin. Several salt depleted (SD) and SIADH patients could be confounded. Usually, adults with SIADH show plasma uric acid values <4 mg/dL. In our elderly population, 41% of SD patients presented plasma uric acid <4 mg/dL, while 27% of SIADH patients showed plasma uric acid >4 mg/dL. Eighty-two percent of SD patients appeared to have plasma urea levels >30 mg/dL, but this was also the case in 21% of SIADH patients. Twenty-nine of the SD patients presented a urinary sodium >30 mEq/L, but all had fractional sodium excretion (FENa) lower than 0.5%. However, in SIADH, 42% of the patients presented also FENa <0.5%. Fractional excretion of urea (FE urea) below 50% was encountered in 82% of SD patients and FE urea above 50% in only 52% of the SIADH patients. Plasma renin and aldosterone values were poorly discriminative. A test infusion with 2 liters isotonic saline over 24 hours allowed a correct classification of all the patients. In about 2/3 of the population, administration of isotonic saline could be considered as useful (SD, most diuretic patients, potomania patients, salt loosing syndrome patients and some SD SIADH patients). A plasma sodium (PNa) increase of at least 5 mEq/L 24 hours after saline infusion has been suggested as highly suggestive of SD. Nevertheless, 29% of our SD patients did not increase their PNa level by 5 mEq/L or more, while 30% of our SIADH patients did. PNa improved after 2 liters isotonic saline over 24 hours in 90 patients (85%) as opposed to 12 others (9 SIADH and 3 diuretic patients), decreasing their plasma sodium. The isotonic saline infusion test, only allows a reliable classification of hyponatremia, as far as both PNa and sodium excretion were taken into account. In the SIADH group, 6 patients (5%) presented initially manifest solute depletion and retained the 2 liters isotonic saline before developping inappropriate natriuresis. Six patients showed a transient salt loosing syndrome with high fractional potassium excretion (FEK) and high calciuria, which differentiates them from thiazide patients presenting also high FEK, but low calciuria. These patients were also polyuric at admission. The saline infusion was well tolerated in all but 2 patients, developing mild pulmonary congestion at the end of the test infusion.

[Treatment of severe hyponatremia (<120mEq/l)]

Inadequate treatment of severe hyponatremia (< 120 mEq/l) can be associated with severe neurological damage. Acute hyponatremia (< 48 h) is usually observed in the postoperative period, these patients need prompt treatment with hypertonic saline (3%) to avoid epilepsia and respiratory arrest. Patients with chronic symptomatic hyponatremia (> 48-72 h) need a rapid correction of SNa the first hours (to decrease brain oedema) followed by a slow correction so that the daily increase in SNa stay under 10 mEq/l/24 h, to avoid the "Osmotic Demyelinating Syndrome" (ODS). Patients with asymptomatic hyponatremia need a slow correction. In patients who are overtreated, decreasing the SNa by giving hypotonic solutions (eventually with DDAVP) so that the daily increase in SNa stays under 10 mEq/l/24 h could protect them again ODS. Frequent measurements of SNa during the correction phase of SNa are mandatory to avoid overcorrection. The use of urea for the management of hyponatremia could represent a good alternative to hypertonic saline. In animals, urea treatment has been clearly shown to protect again ODS, this protective effect could be due to its ability to induce quickly brain "organic osmolytes" reaccumulation.

Difference in solute excretion during correction of hyponatremic patients with cirrhosis or syndrome of inappropriate secretion of antidiuretic hormone by oral vasopressin V2 receptor antagonist VPA-985

VPA-985 is an orally active, competitive vasopressin V(2) receptor antagonist that in normal human beings increases water excretion without affecting solute excretion. Whether solute excretion is affected in patients with hyponatremia resulting from inappropriate secretion of antidiuretic hormone (SIADH) or from cirrhosis treated with VPA-985 is unknown. Six hyponatremic patients with SIADH and 5 hyponatremic patients with cirrhosis with ascitis (CWAs) were treated with 50 or 100 mg VPA-985 twice daily. Evolution of creatinine, urea, uric acid, sodium, potassium, and osmotic clearance were determined. Volume hormones (plasma renin [PR], aldosterone, antidiuretic hormone [ADH], atrial natriuretic factor [ANF]) were also determined before and after treatment. In patients with SIADH, serum sodium concentration (SNa) was generally corrected in 1 day (SNa: 126 +/- 4.5 mmol/L at t = 0 hours and 133 +/- 5.6 mmol/L at t = 24 hours) and associated with a decrease in sodium excretion (from 82 +/- 22 mmol/24 hours to 45 +/- 21 mmol/24 hours; P < 0.05) without modification in potassium excretion. Despite an increase in diuresis (from 0.84 +/- 0.2 ml/min to 1.46 +/- 0.4 ml/min) urea and uric acid clearances decreased. Urine osmolality decreased from 414 +/- 148 mOsm/kg H(2)O to 209 +/- 55 mOsm/kg H(2)O. Volume hormones did not change. In the CWAs the rise of SNa was more progressive (SNa: 126 +/- 2.8 mmol/L at t = H0 to 133 +/- 4.9 mmol/L at t = 48 hours) and parallel to an augmentation in sodium excretion (from 23 +/- 18 mmol/24 hours to 65 6 60 mmol/24 hours the second day of VPA administration). The higher sodium excretion was also connected with a progression in potassium excretion (from 22 6 7 mmol/24 hours to 36 +/- 18 mmol/24 hours). The increase in diuresis under VPA from 0.42 +/- 0.2 mL/min to 1.7 +/- 0.9 mL/min resulted in a higher urea clearance. Urine osmolality decreased from 509 +/- 142 mOsm/kg H(2)O before VPA to 194 +/- 106 mOsm/kg H(2)O after VPA. ADH increased in CWAs treated with VPA, from 1.9 +/- 1.2 pg/mL to 5.3 +/- 2.8 pg/mL (P <.05) while other volume hormones did not change. VPA-985 is a highly effective drug in the short-term management of hyponatremic patients with SIADH or CWAs. SNa correction is associated with urinary sodium retention in SIADH, whereas in CWAs a mild increase in sodium excretion is observed.

High 6-thioguanine nucleotide levels and low thiopurine methyltransferase activity in patients with lupus erythematosus treated with azathioprine

Azathioprine (AZA) is characterized by a high interindividual variability in bioavailability and metabolism. AZA is converted into 6-thioguanine nucleotides (6-TGN) to which the immune modifier activity is attributed. The 6-TGN levels are known to be affected by the activity of the key enzyme, thiopurine methyltransferase (TPMT), which is under genetic dependence. The authors measured a significantly lower TPMT activity in 53 women with systemic lupus erythematosus (SLE) (12.2 +/- 2.4 pmol/h/ml RBC; P < 0.01) when compared with 30 healthy control participants (13.15 +/- 3.1 pmol/h/ml RBC) but not with 28 patients with other dysimmune diseases (non-SLE; 13.0 +/- 3.0 pmol/h/ml RBC; P = 0.10). To evaluate the impact of TPMT activity on the concentrations of AZA metabolites, we measured the TPMT activity and 6-TGN levels in a subgroup of 26 patients in remission and treated with a stable dose of AZA (mean value: 1.9 +/- 0.5 mg/kg/day) for at least six months (n = 13 with SLE and n = 13 with other dysimmune diseases, ie, non-SLE). In such a subgroup, no correlation between 6-TGN levels and TPMT activity was observed. However, patients with SLE presented lower TPMT activity and higher 6-TGN levels (215 +/- 123 versus 140 +/- 75 pmol/8 x 10(8) RBC in non-SLE patients; P < 0.04). It must be noted that transient increase in 6-methylmercaptopurine levels (6-MMP), a putative toxic metabolite (up to 21.7 nmol/8 x 10(8) RBC), was more frequently observed in the non-SLE group (P < 0.01). Even if a relationship was observed between low TPMT activity and 6-TGN levels in SLE, its clinical impact appears to be limited as far as regular hematologic controls are performed.

Evidence that chronicity of hyponatremia contributes to the high urate clearance observed in the syndrome of inappropriate antidiuretic hormone secretion

The high fractional excretion (FE) of uric acid observed in hyponatremia associated with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is commonly attributed to the volume-expanded state, although volume expansion in normonatremic volunteers is unable to increase urate clearance to a degree similar to that in SIADH. The goal of the present study is to analyze whether hyponatremia by itself could influence the FE of uric acid, as well as the effects of intravascular volume and glomerular filtration rate on FE of uric acid in SIADH. This study examines the effects of a 2-L infusion of isotonic saline over 24 hours on FE of uric acid in 9 normonatremic volunteers and 17 hyponatremic patients with SIADH. We also studied the FE of uric acid in 6 patients with SIADH with only mild water retention and the urate and creatinine clearances in 18 hyponatremic patients with SIADH before and after normalization of serum sodium levels by water restriction. When infusing 2 L of isotonic saline over 24 hours in healthy subjects, there was a decrease in plasma protein concentration of 8%, suggesting a similar degree of volume expansion than in patients with SIADH. The FE of uric acid did not increase to the same extent (9% +/- 1.5% versus 17% +/- 1.5%; P: < 0.01). Conversely, in 6 hyponatremic patients with mild water retention (1 L), the FE of uric acid was still high despite indirect signs of only a small increase in plasma volume. The mainstay of these observations is that chronicity of hyponatremia by itself could affect urate excretion. We also observed that in the patients with SIADH, high FE of uric acid inversely correlated with glomerular filtration rate (r = -0.66; P: < 0.01) only during the hyponatremic state. These data suggest that hyponatremia by itself, combined with mild volume expansion and glomerular filtration rate, has a role in the high FE of uric acid in the SIADH.

Relationship between red cell mean corpuscular volume and 6-thioguanine nucleotides in patients treated with azathioprine

Azathioprine (AZA) is characterized by high interindividual differences in bioavailability and metabolization. The aim of the present study was to analyze, in patients treated with AZA for various immune system disorders, whether the variation in red blood cell mean corpuscular volume (deltaMCV) could be used as an indirect estimation of the level of the active immune modifier metabolite 6-thioguanine nucleotides (6-TGN). In 43 consecutive patients treated with a stable dose of AZA for at least 6 months who were not initially anemic, the erythrocyte 6-TGN levels with routine hematologic parameters were determined two to four times at 1-month intervals. In most patients MCV significantly increased after 3 months of therapy and stabilized after 6 months. The correlation between the daily dose of AZA and the 6-TGN level was mild (r = 0.51; P<.001). A weak correlation was also found between the dose of AZA and the deltaMCV after at least 6 months of therapy (r = 0.36; P<.05). The correlation between deltaMCV and 6-TGN level, however, was much better (r = 0.74; P<.001). The lack of a significant increase in MCV after 3 to 4 months of AZA therapy reflects low 6-TGN levels, sometimes a result of undertreatment. A determination of the 6-TGN level during the first months after AZA therapy is begun will allow more accurate adaptation of the effective dose. We observed that deltaMCV could be used as an indicator of 6-TGN levels after 6 months of AZA treatment. An increase in MCV of at least 6 fL is expected to reflect a 6-TGN level of about 175 pmol/8x10(8) red blood cells (probably being within a therapeutic value).

Azotemia (48 h) decreases the risk of brain damage in rats after correction of chronic hyponatremia

Brain myelinolysis complicates excessive correction of chronic hyponatremia in man. Myelinolysis appear in rats for correction levels deltaSNa) > 20 mEq/l/24 h. We previously showed in rats that when chronic hyponatremia was corrected with urea, the incidence and the severity of brain lesions were significantly reduced compared to hypertonic saline. In man, hyponatremia is frequently associated with azotemia and hemo-dialysis usually corrects rapidly the serum sodium (SNa) but only few patients apparently develop demyelination. We hypothesize that uremic state protects brain against myelinolysis. This hypothesis was evaluated in rats developing azotemia by administration of mercuric chloride (HgCl2, 1.5 mg/kg). Severe (SNa < 120 mEq/l) hyponatremia (3 days) was induced by S.C. AVP and i.p. 2.5% D-glucose for 3 days. HgCl2 was injected on day 2. Hyponatremia was corrected on day 4 by i.p. injections of 5% NaCl in order to obtain a correction level largely above the toxic threshold for brain (deltaSNA approximately 30 mEq/l/24 h). Surviving rats were decapitated on day 10 for brain analysis. In the group with renal failure (Group I, n = 15, urea 59 mmol/l) the outcome was remarkably favourable with only three rats (3/15) dying before day 10 and only one of them (1/3) presenting myelinolysis-related neurologic symptoms. The 12 other rats (80%) survived in Group I without symptoms and brain analysis was normal in all of them despite large correction level (deltaSNa: 32 mEq/l/24 h). On the contrary in nine rats in which HgCl, did not produce significant azotemia (control 1, n = 9, urea: 11 mmol/l), all the rats developed severe neurologic symptoms and eight of them died before day 10. Similar catastrophic outcome was observed in the non-azotemic controls (control 2, no HgCl2 administration, n = 15, urea: 5 mmol/l). All of them developed myelinolysis-related neurologic symptoms and only four of them survived with severe brain lesions (survival 12/15 in Group I vs. 5/24 in pooled controls 1 and 2, p < 0.001). In conclusion, we showed for the first time that chronic hyponatremic rats with azotemia (48 h) tolerated large increases in SNa (approximately 30 mEq/l/24 h) without significant brain damage.

Therapeutic relowering of the serum sodium in a patient after excessive correction of hyponatremia

BACKGROUND

Inappropriate correction of chronic hyponatremia could lead to major neuropathological sequelae. In man, the risk of brain myelinolysis increases strikingly when correction of the serum sodium exceeds 10-15 mEq/l/24 h. No treatment is actually available for this iatrogenic brain injury. However, recent experimental data showed that rapid reinduction of the hyponatremia greatly reduces the incidence of brain damage and death in case of serum sodium overshooting.

SUBJECTS AND METHODS

We tested this rescue manoeuver in a 71-year-old woman with nausea, confusion and severe (SNa 106 mEq/l) chronic hyponatremia related to thiazides. It was associated with hypokalemia (SK: 3.2 mEq/l).

RESULTS

Treatment with isotonic saline produced inappropriately high SNa correction level of +21 mEq/l after the first 24 h. After initial improvement, the neurological status deteriorated after 72 h. Rapid reinduction of the hyponatremia was then ordered. Administration of hypotonic fluids (by oral and i.v. route) combined with dDAVP induced a prompt decline in the SNa (-16 mEq/l/14 h) with a final gradient of correction of deltaSNa +9 mEq/l. This manoeuver was well tolerated without untoward effects. The natremia then progressively normalized and the patient completely recovered without neurological sequelae.

CONCLUSION

Hypotonic fluids may be safely administered to decrease the natremia after excessive correction of hyponatremia for potential prevention of myelinolysis.

Treating the syndrome of inappropriate ADH secretion with isotonic saline

It has been widely accepted that there is little use for saline treatment in the syndrome of inappropriate secretion of ADH (SIADH). However, having observed that most SIADH patients increased their plasma sodium (PNa) after 2 l isotonic saline over 24 h, we investigated whether urine osmolality or the sum of urinary sodium and potassium (UNa + K) predicted this response, in 17 consecutive patients with chronic SIADH. The initial measure of urinary sodium plus potassium (UNa + K t0) was weakly correlated to the change in PNa (DPNa) after infusion (r = -0.51; p < 0.05), while initial urine osmolality (UOSM t0) was a much better predictor (y = -0.024x + 12.90; r = -0.81; p < 0.001). The lack of predictive value for UNa + K t0 was probably because urine electrolyte concentrations were not maximal for the corresponding initial UOSM. This reflects differences in salt intake between the patients. The theoretical maximal value for UNa + K t0 (th max UNa + K t0) for a given USOM t0, was as good a predictor as UOSM t0 (th max UNa + K vs. DPNa: r = -0.81; p < 0.001). A theoretical model describing the effect of 2 l isotonic saline infusion on DPNa as a function of UNa + K, produced values comparable to those observed in our patients. Only 6/17 patients, those with UOSM > 530 mOsm/kg, had their hyponatraemia aggravated by 2 l isotonic saline. Many SIADH patients have lower UOSM; in most such patients, 2 l of isotonic saline will improve PNa.

Restoration of the uricosuric effect of probenecid after triglycylvasopressine administration in a gouty patient

A 35-year-old patient with severe gout and mild renal insufficiency presented very low urinary urate excretion. Volume expansion induced by fludrocortisone combined or not with a uricosuric drug (Benzbromarone) was unable to significantly increase his urate excretion. A combined Probenecid (PB) and Pyrazinamide (PZA) test was performed. These drugs being considered to affect renal tubular reabsorption or secretion. No significant modification of uric acid fractional excretion (FE.uric acid) was observed after PB and PZA. When the same test was performed after the administration of Triglycyl-lysine vasopressine (TGLV), a potent V1 receptor stimulator, we observed a three fold increase in FE.uric acid after PB intake (from 6 to 18%) followed by a decrease after PZA (from 18 to 5.6%). When TGLV was administered alone their was no significant modification of uric acid fractional excretion. We propose that TGLV decrease proximal tubular urate reabsorption that could only be detected when postsecretory reabsorption is blocked by an uricosuric drug.

The treatment of severe hyponatremia

Severe hyponatremia may be chronic (days) or acute (hours), symptomatic or asymptomatic. Severe chronic symptomatic hyponatremia (serum sodium concentration < 110 to 115 mM/liter) occurs most commonly in the syndrome of inappropriate antidiuretic hormone secretion (SIADH). The treatment of this hyponatremia is a challenge to practicing physicians, in part because an overly rapid correction of hyponatremia may cause brain damage. The latter sometimes takes the form of central pontine myelinolysis (CPM). On the basis of available clinical and experimental literature, the rate of correction of this symptomatic hyponatremia should be no more than 0.5 mM per liter per hour, and the initial treatment should be halted once a mildly hyponatremic range of the serum sodium concentration has been reached (approximately 125 to 130 mM/liter). In contrast, severe chronic asymptomatic hyponatremia may be treated sufficiently by a fluid restriction. On the other hand, severe symptomatic acute hyponatremia should be treated promptly and rapidly, using hypertonic saline, to initially reach a mildly hyponatremic level.