WBR0398

Author	PageAuthor::Vendhan Ramanujam
Exam Type	ExamType::USMLE Step 2 CK
Main Category	MainCategory::Pediatrics
Sub Category	SubCategory::Endocrine
Prompt	[[Prompt::A 3 year old boy is brought by his mother for the complaint of bowing of his legs to his physicians office. His birth history reveals an uncomplicated vaginal delivery without any birth defects. Mother denies any problem in her family and does not know about the family history of the child's father, whom she had divorced last year. The examination of the child reveals prominent knobs at the costochondral junctions and a horizontal groove along the lower border of the thorax. Lab values turn out as Serum calcium Normal Serum phosphate Decreased Serum alkaline phosphatase Normal Serum parathyroid hormone (PTH) Normal Plasma 25-OH vitamin D Normal Plasma 1,25 Dihydroxy vitamin D Normal What is the possible cause for this child's finding?]]
Answer A	AnswerA::Vitamin D deficiency
Answer A Explanation	[[AnswerAExp::Incorrect-Vitamin D deficiency will have low calcium, low phosphate, increased PTH, low 25-OH vitamin D and low or elevated 1,25 Dihydroxy vitamin D levels. Vitamin D deficiency causes low 25-OH vitamin D and 1,25 Dihydroxy vitamin D levels that will lead to hypocalcemia. Hypocalcemia then triggers a secondary hyperparathyroidism leading to hypophosphatemia and elevated 1,25 Dihydroxy vitamin D levels.]]
Answer B	AnswerB::Type II vitamin D dependent rickets
Answer B Explanation	AnswerBExp::'''Incorrect'''-In type II vitamin D dependent rickets, there is a mutation of vitamin D receptor. Therefore these patients will have a normal serum level of calcitriol, which are ineffective and leading to rickets.
Answer C	AnswerC::X linked hypophosphatemic rickets
Answer C Explanation	[[AnswerCExp::Correct-X linked hypophosphatemic rickets is due to renal phosphate wasting which leads to low serum phosphate levels with normal levels of serum calcium, serum PTH, serum alkaline phosphatase, plasma 25-OH vitamin D and 1,25 dihydroxy vitamin D (calcitriol).]]
Answer D	AnswerD::Renal failure
Answer D Explanation	AnswerDExp::'''Incorrect'''-Patients with renal failure will have low serum calcium, high serum phosphate, low serum calcitriol and increased serum PTH.
Answer E	AnswerE::Pseudo hypoparathyroidism
Answer E Explanation	AnswerEExp::'''Incorrect'''-Patients with pseudo hypoparathyroidism will have low serum calcium, high serum phosphate and high serum PTH. Serum alkaline phosphatase and calcitriol levels will be normal.
Right Answer	RightAnswer::C
Explanation	[[Explanation::X linked hypophosphatemic rickets is due to renal phosphate wasting which leads to low serum phosphate levels with normal levels of serum calcium, serum PTH, serum alkaline phosphatase, plasma 25-OH vitamin D and 1,25 dihydroxy vitamin D (calcitriol). Educational objective: Suspect X linked hypophosphatemic rickets in patients with normal serum calcium, normal serum alkaline phosphatase and normal 25-OH vitamin D. Educational Objective: References: ]]
Approved	Approved::Yes
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