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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{YD}} (Reviewed by  {{YD}} and  {{AJL}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Pathology
|MainCategory=Pathology
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|MainCategory=Pathology
|MainCategory=Pathology
|SubCategory=Musculoskeletal/Rheumatology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Pathology
|MainCategory=Pathology
|MainCategory=Pathology
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|MainCategory=Pathology
|MainCategory=Pathology
|SubCategory=Musculoskeletal/Rheumatology
|SubCategory=Musculoskeletal/Rheumatology
|Prompt=A 12 year old boy is brought by his mother to the physician's clinic for multiple bone fractures and abnormal facial bone. Lab work-up reveals no abnormality.  After further imaging and genetic testing, the diagnosis is made. The physician explains to the mother that her child's condition is caused by primary spongiosa filling the medullary cavity and causing an "Erlenmeyer flask" bones on xray. Which of the following the most likely diagnosis?
|Prompt=A 12-year-old boy is brought by his mother to the physician's office for multiple bone fractures. Although initial lab work-up reveals no abnormality, the diagnosis is initially suspected on x-ray of the femur (shown below). The diagnosis is then confirmed by genetic testing. Which of the following is the most likely diagnosis of this patient?
|Explanation=Osteopetrosis (marble bone disease) is a disease that is characterized by failure of nromal bone resorption. It causes thickening of bones that become dense but more predisposed to fractures.  On xray, "Erlenmeyer flask" appearance of bones is characteristic.  Osteopetrosis is further described as primary spongiosa filling the medullary cavity.  However, the diagnosis may be missed by lab work-up because serum values of calcium, phosphage, and ALP are typically within normal limits.
 
[[File:WBR0474Exp.jpg|200px]]
|Explanation=[[Osteopetrosis]] (marble bone disease) is a rare heritable disease characterized by increased bone density on imaging. Autosomal recessive (classic or malignant) form is severe and manifests as early fractures, short stature, compressive neuropathies, pancytopenia due to primary spongiosa filling the medullary cavity, hypocalcemia, and early death within the first 10 years of life. The autosomal recessive form is also associated with renal tubular acidosis and is thus thought to be involved in mutations of carbonic anhydrase II (CAII), an anion exchanger that has a role in kidney function and the provision of the acidic environment needed for bone resorption.


The primary defect in osteopetrosis is believed to be due to abnormal functioning of osteoclasts, which are derived from monocyte lineage.  As a result, bone marrow transplantation (BMT) is thought to be the only appropriate cure for patients with osteopetrosis.
In contrast, the autosomal dominant form is more likely to manifest at older age during late childhood or adolescence, as presented in this vignette. Osteopetrosis is caused by failure of osteoclast development, differentiation, and function due to one of many genetic mutations. Osteopetrosis results in dense, thick bones that are paradoxically predisposed to fractures. A generalized increased bone density and an "Erlenmeyer flask" appearance of bones are characteristic on x-ray (shown below). Patients often present with multiple bone fractures, scoliosis, and mandible-osteomyelitis due to dental abscesses or caries. The diagnosis may be overlooked by lab work-up because serum values of calcium, phosphate, and alkaline phosphatase (ALP) are typically within normal limits in the autosomal dominant form. Treatment of ostepetrosis is generally symptomatic. Since the primary defect in [[osteopetrosis]] is abnormal functioning of osteoclasts, which are derived from monocyte lineage, bone marrow transplantation (BMT) is thought to be the only appropriate cure for patients with [[osteopetrosis]].  


Educational Objective:
[[Image:WBR0474Exp.jpg|200px]]
Osteopetrosis is characterized by failure of normal bone resorption due to defect of osteoclasts. In osteopetrosis, primary spongiosa fills the medullary cavity.  Lab values are usually within normal limits.  Xray often shows visible "Erlenmeyer flask" bones
|AnswerA=Osteoporosis
|AnswerA=Osteoporosis
|AnswerAExp=Osteoporosis is characterized by loss of interconnections of trabeculated bone.
|AnswerAExp=[[Osteoporosis]] is characterized by the loss of interconnections of trabeculated bone.
|AnswerB=Osteopetrosis
|AnswerB=Osteopetrosis
|AnswerBExp=Osteopetrosis is characterized by primary spongiosa filling the medullary cavity.
|AnswerBExp=[[Osteopetrosis]] is characterized by diffuse bone thickenening and Erlenmeyer flask appearance on x-ray.
|AnswerC=Paget's disease
|AnswerC=Paget's disease of the bone
|AnswerCExp=Paget's disease is characterized by abnormal bone architecture with mosaic bone pattern that cause long bone chalk-stick fractures.
|AnswerCExp=[[Paget's disease]] of the bone is characterized by abnormal bone architecture that manifests as a mosaic bone pattern and results in long bone chalk-stick fractures.
|AnswerD=Osteomalacia
|AnswerD=Osteomalacia
|AnswerDExp=Osteomalacia is characterized by defective mineralization or calcification of osteoid.
|AnswerDExp=[[Osteomalacia]] is characterized by the defective mineralization or calcification of osteoid that is usually caused by vitamin D deficiency in adults. In contrast, vitamin D deficiency in children results in [[rickets]].
|AnswerE=Polyostotic fibrous dysplasia
|AnswerE=Polyostotic fibrous dysplasia
|AnswerEExp=Polyostotic fibrous dysplasia is characterized by the replacement of bone by fibroblasts, colalgen, and irregular bone trabeculae.
|AnswerEExp=[[Polyostotic fibrous dysplasia]] is characterized by the presence of irregular bone trabeculae due to the replacement of bone by fibroblasts.
|EducationalObjectives=Osteopetrosis is caused by failure of osteoclast development, differentiation, and function due to one of many genetic mutations. The autosomal dominant form of osteopetrosis results in dense, thick bones that are paradoxically predisposed to fractures in late childhood or adolescence. A generalized increased bone density and an "Erlenmeyer flask" appearance of bones are characteristic on x-ray.
|References=Stark Z, Savarirayan R. Osteopetrosis. Orphanet J Rare Dis. 2009;4:5.<br>
First Aid 2014 page 420
|RightAnswer=B
|RightAnswer=B
|WBRKeyword=osteopetrosis, marble, bone, disease, marble bone disease, calcium, phosphate, ALP, alkaline, phosphatase, alkaline phosphatase, osteoclast, defect, bone, marrow, transplantation, bone marrow transplantation, BMT, spongiosa, medullary, cavity, flask, erlenmeyer, xray
|WBRKeyword=Osteopetrosis, Marble bone disease, Erlenmeyer flask, X-ray, Osteoclasts, Bone resorption
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 00:41, 28 October 2020

 
Author [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Pathology
Sub Category SubCategory::Musculoskeletal/Rheumatology
Prompt [[Prompt::A 12-year-old boy is brought by his mother to the physician's office for multiple bone fractures. Although initial lab work-up reveals no abnormality, the diagnosis is initially suspected on x-ray of the femur (shown below). The diagnosis is then confirmed by genetic testing. Which of the following is the most likely diagnosis of this patient?

]]

Answer A AnswerA::Osteoporosis
Answer A Explanation [[AnswerAExp::Osteoporosis is characterized by the loss of interconnections of trabeculated bone.]]
Answer B AnswerB::Osteopetrosis
Answer B Explanation [[AnswerBExp::Osteopetrosis is characterized by diffuse bone thickenening and Erlenmeyer flask appearance on x-ray.]]
Answer C AnswerC::Paget's disease of the bone
Answer C Explanation [[AnswerCExp::Paget's disease of the bone is characterized by abnormal bone architecture that manifests as a mosaic bone pattern and results in long bone chalk-stick fractures.]]
Answer D AnswerD::Osteomalacia
Answer D Explanation [[AnswerDExp::Osteomalacia is characterized by the defective mineralization or calcification of osteoid that is usually caused by vitamin D deficiency in adults. In contrast, vitamin D deficiency in children results in rickets.]]
Answer E AnswerE::Polyostotic fibrous dysplasia
Answer E Explanation [[AnswerEExp::Polyostotic fibrous dysplasia is characterized by the presence of irregular bone trabeculae due to the replacement of bone by fibroblasts.]]
Right Answer RightAnswer::B
Explanation [[Explanation::Osteopetrosis (marble bone disease) is a rare heritable disease characterized by increased bone density on imaging. Autosomal recessive (classic or malignant) form is severe and manifests as early fractures, short stature, compressive neuropathies, pancytopenia due to primary spongiosa filling the medullary cavity, hypocalcemia, and early death within the first 10 years of life. The autosomal recessive form is also associated with renal tubular acidosis and is thus thought to be involved in mutations of carbonic anhydrase II (CAII), an anion exchanger that has a role in kidney function and the provision of the acidic environment needed for bone resorption.

In contrast, the autosomal dominant form is more likely to manifest at older age during late childhood or adolescence, as presented in this vignette. Osteopetrosis is caused by failure of osteoclast development, differentiation, and function due to one of many genetic mutations. Osteopetrosis results in dense, thick bones that are paradoxically predisposed to fractures. A generalized increased bone density and an "Erlenmeyer flask" appearance of bones are characteristic on x-ray (shown below). Patients often present with multiple bone fractures, scoliosis, and mandible-osteomyelitis due to dental abscesses or caries. The diagnosis may be overlooked by lab work-up because serum values of calcium, phosphate, and alkaline phosphatase (ALP) are typically within normal limits in the autosomal dominant form. Treatment of ostepetrosis is generally symptomatic. Since the primary defect in osteopetrosis is abnormal functioning of osteoclasts, which are derived from monocyte lineage, bone marrow transplantation (BMT) is thought to be the only appropriate cure for patients with osteopetrosis.


Educational Objective: Osteopetrosis is caused by failure of osteoclast development, differentiation, and function due to one of many genetic mutations. The autosomal dominant form of osteopetrosis results in dense, thick bones that are paradoxically predisposed to fractures in late childhood or adolescence. A generalized increased bone density and an "Erlenmeyer flask" appearance of bones are characteristic on x-ray.
References: Stark Z, Savarirayan R. Osteopetrosis. Orphanet J Rare Dis. 2009;4:5.
First Aid 2014 page 420]]

Approved Approved::Yes
Keyword WBRKeyword::Osteopetrosis, WBRKeyword::Marble bone disease, WBRKeyword::Erlenmeyer flask, WBRKeyword::X-ray, WBRKeyword::Osteoclasts, WBRKeyword::Bone resorption
Linked Question Linked::
Order in Linked Questions LinkedOrder::