PseudoBartter syndrome and Eating disorders

PseudoBartter’s syndrome, a complex pattern of seemingly unrelated metabolic abnormalities, is frequently seen in patients with eating disorders, particularly those who indulge in purging behaviors. We present two cases that, despite divergent background histories and clinical presentations, possess the unifying pathophysiology that ultimately leads to this syndrome. The metabolic and clinical manifestations of PseudoBartter’s syndrome are seen more commonly than previously thought. It is important to appreciate that a complex self-perpetuating pathophysiology leads to the hypokalemic metabolic alkalosis characteristic of PseudoBartter syndrome. The metabolic abnormalities characteristic of this phenomenon should therefore be viewed in this context and the resulting predilection towards marked edema formation should be borne in mind

Bartter syndrome is a rare inherited defect in the thick ascending limb of the loop of Henle. It is characterized by low potassium levels (hypokalemia),increased blood pH (alkalosis), and normal to low blood pressure. There are two types of Bartter syndrome: neonatal and classic. A closely associated disorder, Gitelman syndrome, is milder than both subtypes of Bartter syndrome. The condition is named after Dr. Frederic Bartter, who, along with Dr. Pacita Pronove, first described it in 1960 and in more patients in 1962.

A condition attributed to furosemide therapy, characterized by hypokalemic-hypochloremic alkalosis, hyperactivity of renin-angiotensin-aldosterone system with ↑ aldosterone, normotension, pressor inactivity of angiotensin II, ↑ urinary PGE2, ANP. Cf Bartter syndrome.

An uncommon cause of metabolic alkalosis that has been seen as a presenting feature of CF as well as a complication in those with known disease. It is accompanied by chronic salt depletion and sometimes failure to thrive without severe dehydration. Principal findings are hypokalaemic hypochloraemic metabolic alkalosis, sometimes with hyponatraemia. This may be preceded by anorexia, nausea, vomiting, respiratory exacerbations, fever and weight loss.

Clinical Manifestation

In 90% of cases, neonatal Bartter syndrome is seen between 24 and 30 weeks of gestation with excess amniotic fluid (polyhydramnios). After birth, the infant is seen to urinate and drink excessively (polyuria, and polydipsia, respectively). Life-threatening dehydration may result if the infant does not receive adequate fluids. About 85% of infants dispose of excess amounts of calcium in the urine (hypercalciuria) and kidneys (nephrocalcinosis), which may lead to kidney stones. In rare occasions, the infant may progress to renal failure.

Patients with classic Bartter syndrome may have symptoms in the first two years of life, but they are usually diagnosed at school age or later. Like infants with the neonatal subtype, patients with classic Bartter syndrome also have polyuria, polydipsia, and a tendency to dehydration, but normal or just slightly increased urinary calcium excretion without the tendency to develop kidney stones. These patients also have vomiting and growth retardation. Kidney function is also normal if the disease is treated,[2] but occasionally patients proceed to end-stage renal failure. Bartter’s syndrome consists of hypokalaemia, alkalosis, normal to low blood pressures, and elevated plasma renin and aldosterone. Numerous causes of this syndrome probably exist. Diagnostic pointers include high urinary potassium and chloride despite low serum values, increased plasma renin, hyperplasia of the juxtaglomerular apparatus on renal biopsy, and careful exclusion of diuretic abuse. Excess production of renal prostaglandins is often found. Magnesium wasting may also occur.

Diagnosis

People suffering from Bartter syndrome present symptoms that are identical to those of patients who are on loop diuretics like furosemide.

The clinical findings characteristic of Bartter syndrome are hypokalemia, metabolic alkalosis, and normal to low blood pressure. These findings may also be caused by:

  • Chronic vomiting: These patients will have low urine chloride levels (Bartter’s will have relatively higher urine chloride levels).
  • Abuse of diuretic medications (water pills): The physician must screen urine for multiple diuretics before diagnosis is made.
  • Magnesium deficiency and Calcium deficiency: These patients will also have low serum and urine magnesium and calcium

Patients with Bartter syndrome may also have elevated renin and aldosterone levels.

Prenatal Bartter syndrome can be associated with polyhydramnios.

Pathophysiology

Bartter syndrome is caused by mutations of genes encoding proteins that transport ions across renal cells in the thick ascending limb of the nephron.

Bartter and Gitelman syndromes can be divided into different subtypes based on the genes involved:[5]

Name Bartter type Associated gene mutations Defect
neonatal Bartter’s syndrome type 1 SLC12A2 (NKCC2) Na-K-2Cl symporter
neonatal Bartter’s syndrome type 2 ROMK/KCNJ1 thick ascending limb K+ channel
classic Bartter’s syndrome type 3 CLCNKB Cl- channel
Bartter’s syndrome with sensorineural deafness type 4 BSND[6] Cl- channel accessory subunit
Bartter’s syndrome associated with autosomal dominant hypocalcemia type 5 CASR[7] activating mutation of the calcium-sensing receptor
Gitelman’s syndrome - SLC12A3 (NCCT) Sodium-chloride symporter

Treatment

  • While patients should be encouraged to include liberal amounts of sodium[citation needed] and potassium in their diet, potassium supplements are usually required, and spironolactone is also used to reduce potassium loss.
  • Nonsteroidal antiinflammatory drugs (NSAIDs) can be used as well, and are particularly helpful in patients with neonatal Bartter’s syndrome.
  • Angiotensin-converting enzyme (ACE) inhibitors can also be used.
  • Check venous sample in blood gas machine for bicarbonate. However after salt replacement, the metabolic abnormality resolves and weight gain follows rapidly. Treatment is with sodium and/or potassium chloride supplements, which may be required for many months. Unexplained failure to thrive should always have urinary electrolytes checked, a spot urine Na+ <20 mmol/l indicates low total body sodium that needs correcting. A serum potassium at the lower end of the normal range may still be associated with body depletion.
  • It is quite usual for a newborn screened infant under 3 months to have low urine Na levels. The normal range is less well defined so if they are thriving, we do not treat this with sodium supplements.

Prognosis

The limited prognostic information available suggests that early diagnosis and appropriate treatment of infants and young children with Classic Bartter Syndrome may improve growth and perhaps neurointellectual development. On the other hand, sustained hypokalemia and hyperreninemia can cause progressive tubulointerstitial nephritis, resulting in end-stage-renal disease (Kidney failure). With early treatment of the electrolyte imbalances the prognosis for patients with Classic Bartter Syndrome is good.

Related conditions

  • Bartter and Gitelman syndromes are both characterized by hypokalemia, hypomagnesemia, normal to low blood pressure, and hypochloremic metabolic alkalosis.[11]
  • However, Bartter syndrome is also characterized by high renin, high aldosterone, hypercalciuria, and an abnormal Na+-K+-2Cl- transporter in the thick ascending limb of the loop of Henle, Gitelman syndrome causes hypocalciuria and is due to an abnormal thiazide transporter in the distal segment.
  • Pseudo-Bartter’s syndrome is a syndrome of similar presentation as Bartter syndrome but without any of its characteristic genetic defects. Pseudo-Bartter’s syndrome has been seen in cystic fibrosis, as well as in excessive use of laxatives.

References

  • Naesens M, Steels P, Verberckmoes R, Vanrenterghem Y, Kuypers D (2004). “Bartter’s and Gitelman’s syndromes: from gene to clinic”. Nephron Physiol 96 (3): p65–78. doi:10.1159/000076752. PMID 15056980.
  • Zaffanello M, Taranta A, Palma A, Bettinelli A, Marseglia GL, Emma F (2006). “Type IV Bartter syndrome: report of two new cases”. Pediatr. Nephrol. 21 (6): 766–70.
  • Vezzoli G, Arcidiacono T, Paloschi V, et al. (2006). “Autosomal dominant hypocalcemia with mild type 5 Bartter syndrome”. J. Nephrol. 19 (4): 525–8.
  • Bartter Syndrome: Tubular and Cystic Kidney Disorders: Merck Manual Home Edition”. Archived from the original on 4 January 2008. Retrieved 2007-12-31.
  • Reproduced in Bartter FC, Pronove P, Gill JR, MacCardle RC (1998). “Hyperplasia of the juxtaglomerular complex with hyperaldosteronism and hypokalemic alkalosis. A new syndrome. 1962″. J. Am. Soc. Nephrol. 9 (3): 516–28. 
  • Dane B, Yayla M, Dane C, Cetin A (2007). “Prenatal diagnosis of Bartter syndrome with biochemical examination of amniotic fluid: case report”. Fetal. Diagn. Ther. 22 (3): 206–8. 
  • Proesmans W (2006). “Threading through the mizmaze of Bartter syndrome”. Pediatr. Nephrol. 21 (7): 896–902.
  • Royal Brompton & Harefield Hospital > Pseudo-Bartter’s syndrome Retrieved Mars, 2011

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