WBR0145

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Genetics
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 successfully met previous developmental milestones. The patient’s vital signs reveal a temperature of 37.2 C (99.0F), pulse of 140 bpm, and blood pressure of 70/50 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 the latter, Gitelman syndrome reveals electrolyte values as as if someone is on thiazide diuretics with absence of elevated urinary calcium levels. Gitelman syndrome usually presents later than 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 rare inherited form of hypokalemic metabolic alkalosis. It is characterized by polyuria, polydypsia, and signs of dehydration on physical examination. Serum and urinary electrolytes would be similar to patients on loop diuretics, with elevated urinary calcium and potassium. 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. Affected patients are unable to reabsorb adequate sodium in the ascending loop of Henle. Blood volume decreases due to sodium loss, and the renin-angiotensin-aldosterone-system is activated. Aldosterone is therefore elevated, which causes a loss of potassium ions and their coupled hydrogen ions (metabolic alkalosis). Educational Objective: Bartter syndrome causes hypokalemic metabolic alkalosis similar to patients on loop diuretics, but manifests at an early age. References: 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
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