WBR0531

Author	PageAuthor::Vendhan Ramanujam
Exam Type	ExamType::USMLE Step 2 CK
Main Category	MainCategory::Internal medicine
Sub Category	SubCategory::Endocrine, SubCategory::Musculoskeletal/Rheumatology
Prompt	[[Prompt::A 74 year old male complaining of hip pain arrives at his physicians office. He also complaints of headache, hearing loss, and tinnitus. On physical exam the skull appears to be enlarged, with prominent superficial veins. There is marked kyphosis, and the bones of the leg appear to be deformed. Lab tests reveal an elevated plasma alkaline phosphatase level. A skull x-ray shows sharply demarcated lucencies in the frontal, parietal, and occipital bones. X-rays of the hip show thickening of the pelvic brim. Which one of the following is the most likely mechanism of the patient’s condition?]]
Answer A	AnswerA::Defective bone mineralization
Answer A Explanation	[[AnswerAExp::Incorrect-Defective bone mineralization occurs in vitamin D deficiency due to decreased calcium and phosphorus availability at mineralization sites.]]
Answer B	AnswerB::Normal mineralization with low bone mass
Answer B Explanation	[[AnswerBExp::Incorrect-Normal mineralization with low bone mass is characteristic of osteoporosis.]]
Answer C	AnswerC::Abundant mineralization of the periosteum
Answer C Explanation	[[AnswerCExp::Incorrect-Abundant mineralization of periosteum can be seen in hypervitaminosis A.]]
Answer D	AnswerD::Abnormal bone remodeling
Answer D Explanation	[[AnswerDExp::Correct-Abnormal bone remodeling is the primary defect where excessive resorption of bone due to excess osteoclastic activity is followed by replacement of normal marrow with dense, trabecular and disorganized bone due to activation of osteoblastic activity in Pagets disease.]]
Answer E	AnswerE::Defective bone and cartilage mineralization
Answer E Explanation	[[AnswerEExp::Incorrect-Defective bone and cartilage mineralization can be seen in rickets following vitamin D deficiency, but only in children.]]
Right Answer	RightAnswer::D
Explanation	[[Explanation::This patient has Pagets disease of bone. Enlarged skull, headaches and hearing loss with tinnitus, due to the direct involvement of the ossicles of the inner ear are the common sign and symptoms. Abnormal bone remodeling is the primary defect where excessive resorption of bone due to excess osteoclastic activity is followed by replacement of normal marrow with dense, trabecular and disorganized bone due to activation of osteoblastic activity. Thus a normal lamellar bone with woven pattern becomes chaotic with a mosaic pattern. Plasma alkaline phosphatase levels represent the increased bone turnover. Educational Objective: The pathophysiology mechanism of Pagets disease is abnormal bone remodeling. Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Paget disease of the bone
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