WBR0145

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Will Gibson)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology
Sub Category	SubCategory::Renal
Prompt	[[Prompt::A 2-year-old girl is brought to the pediatrician by her mother for excessive drinking and urination. The patient’s mother recalls an uneventful pregnancy and delivery. The patient had a normal neonatal growth course and has successfully met previous developmental milestones. The patient’s vital signs are a temperature of 37.2 C (99.0F), pulse of 140 bpm, and blood pressure of 110/80 mmHg. On physical examination, the patient’s skin turgor shows delayed recoil and her extremities are mottled and cyanotic. Physical examination is otherwise unremarkable. Laboratory testing is significant for metabolic alkalosis, hypokalemia, elevated plasma renin and aldosterone. Urinalysis reveals markedly elevated urinary calcium and potassium with no evidence of casts, hematuria, or leukocyturia. What is the most likely diagnosis?]]
Answer A	AnswerA::21-hydroxylase deficiency
Answer A Explanation	[[AnswerAExp::21 hydroxylase deficiency, a form of congenital adrenal hyperplasia, typically presents with hypotension, but also with hyperkalemia and signs of masculinization due to female hermaphrodism. These findings are absent in this patient.]]
Answer B	AnswerB::Gitelman syndrome
Answer B Explanation	[[AnswerBExp::Gitelman syndrome should be included in the differential diagnosis of Bartter syndrome. Unlike Barrter syndrome, Gitelman syndrome is characterized by electrolyte values similar to an individual administered thiazide diuretics with absence of elevated urinary calcium levels. Similar to Barrter syndrome, Gitelman syndrome also causes metabolic alkalosis and hypokalemia. However, Gitelman syndrome is not associated with nephrocalcinosis (no elevation in urinary calcium), is less severe, and usually presents later compared to Bartter syndrome.]]
Answer C	AnswerC::Secreting pituitary tumor
Answer C Explanation	[[AnswerCExp::The most common secreting pituitary tumor would be a prolactinoma, which presents in adults with bilateral hemianopsia, galactorrhea and amenorrhea. In children, it causes headache and growth arrest. Another possible tumor would be a growth hormone secreting tumor, which would cause accelerated growth. This child has none of these symptoms.]]
Answer D	AnswerD::Bartter syndrome
Answer D Explanation	[[AnswerDExp::Bartter syndrome is a rare inherited form of hypokalemic metabolic alkalosis. Serum and urinary electrolytes would be similar to patients on loop diuretics, with elevated urinary calcium and potassium.]]
Answer E	AnswerE::Lipoid nephrosis
Answer E Explanation	[[AnswerEExp::Lipoid nephrosis, or minimal change disease, is a glomuerulonephritis characterized by normal-appearing glomeruli under light microscopy. Electron microscopy, however, reveals foot process effacement with selective loss of albumin. Minimal change disease is a type of nephritic syndrome that would not have the presentation of the patient in the vignette.]]
Right Answer	RightAnswer::D
Explanation	[[Explanation::Bartter syndrome is a group of autosomal recessive renal tubular diseases that are characterized by impaired salt reabsorption in the thick ascending loop of Henle (TAL). It is an inherited form of hypokalemic metabolic alkalosis. Defects in at least 5 genes involved in ion transport across renal cells in the thick ascending loop of Henle have been implicated in Bartter syndrome. It is characterized by polyuria, polydypsia, and signs of dehydration on physical examination. Clinically, Bartter syndrome is suspected when young patients present with signs and symptoms similar to those administered loop diuretic, which has a similar mechanism of action at the level of the ascending loop of Henle. Accordingly, serum and urinary electrolytes would be similar to patients on loop diuretics, with elevated urinary calcium and potassium. Elevated urinary calcium levels predispose patients to nephrocalcinosis. Affected patients are unable to reabsorb adequate sodium in the ascending loop of Henle. Blood volume decreases due to sodium loss, and activation of the renin-angiotensin-aldosterone-system ensues. Aldosterone is therefore elevated, which causes a loss of potassium ions and hydrogen ions (metabolic alkalosis). Blood pressure among patients with Bartter syndrome may be normal or low. Educational Objective: Bartter syndrome causes hypokalemic metabolic alkalosis similar to patients on loop diuretics but manifests at an early age. References: Hebert SC. Bartter syndrome. Curr Opin Nephrol & Hypertens. 2003;12(5):527-32. First Aid 2014 page 529]]
Approved	Approved::Yes
Keyword	WBRKeyword::Renal, WBRKeyword::Bartter syndrome, WBRKeyword::Aldosterone, WBRKeyword::Renin, WBRKeyword::RAAS, WBRKeyword::Metabolic alkalosis, WBRKeyword::Electrolyte, WBRKeyword::Loop of Henle, WBRKeyword::Loop, WBRKeyword::Henle, WBRKeyword::Diuretic
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