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1. General Principles & Basic Science MCQs

Practice Set 741 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 14801

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy is diagnosed with Camurati-Engelmann disease based on classic radiographic findings of bilateral femoral diaphyseal thickening and a confirmed TGFB1 mutation. He reports severe, debilitating leg pain and progressive muscle weakness. Which of the following is the most effective medical therapy for his symptoms?

. Bisphosphonates
. Systemic corticosteroids
. Non-steroidal anti-inflammatory drugs (NSAIDs) alone
. Vitamin D and Calcium supplementation
. Enzyme replacement therapy

Correct Answer & Explanation

. Systemic corticosteroids

Explanation

Systemic corticosteroids are the mainstay of medical treatment for symptomatic Camurati-Engelmann disease. They have been shown to significantly decrease bone pain, improve muscle strength, and in some cases, reverse the abnormal radiographic findings.

Question 14802

Topic: 1. General Principles & Basic Science

When differentiating a chondromyxoid fibroma from a chondroblastoma based on standard radiographic presentation in a skeletally immature patient, which of the following features most strongly favors a diagnosis of chondroblastoma?

. Eccentric location
. Lytic appearance with a sclerotic rim
. Intracortical location
. Epiphyseal location
. Presence of internal septations

Correct Answer & Explanation

. Epiphyseal location

Explanation

In a skeletally immature patient, a chondroblastoma is classically located within the epiphysis (or apophysis). Chondromyxoid fibroma, conversely, is almost always found in the metaphysis.

Question 14803

Topic: Biology, Genetics & Bone Healing

A newborn presents with micromelic shortening of the limbs, severe clubfeet, rigid "hitchhiker" thumbs, and cystic swelling of the pinnae. Radiographs show a first metacarpal that is short and oval-shaped. Which of the following is the defective cellular process in this dysplasia?

. Type 1 collagen synthesis
. Fibroblast growth factor receptor signaling
. Transmembrane sulfate transport
. Cartilage oligomeric matrix protein secretion
. Osteoclast-mediated bone resorption

Correct Answer & Explanation

. Transmembrane sulfate transport

Explanation

The clinical description is pathognomonic for diastrophic dysplasia (hitchhiker thumb, cauliflower ear, severe clubfeet). This is caused by a mutation in the SLC26A2 gene, which encodes a transmembrane sulfate transporter essential for cartilage matrix sulfation.

Question 14804

Topic: 1. General Principles & Basic Science

A 5-year-old boy presents with progressive joint stiffness, coarse facial features, and hepatosplenomegaly. An ophthalmologic exam reveals clear corneas. His maternal uncle had similar clinical features and died of cardiac failure in his twenties. Which of the following enzyme deficiencies is most likely responsible for this condition?

. Alpha-L-iduronidase
. Iduronate-2-sulfatase
. Galactose-6-sulfatase
. Arylsulfatase B
. Heparan N-sulfatase

Correct Answer & Explanation

. Iduronate-2-sulfatase

Explanation

This patient has Hunter syndrome (MPS II), which is unique among mucopolysaccharidoses because it is inherited in an X-linked recessive pattern and features clear corneas. It is caused by a deficiency in iduronate-2-sulfatase.

Question 14805

Topic: 1. General Principles & Basic Science

A 10-year-old girl is diagnosed with Progressive Diaphyseal Dysplasia (Camurati-Engelmann disease). She complains of debilitating bone pain in her bilateral lower extremities. Which of the following is the most appropriate first-line medical therapy to alleviate her symptoms?

. Intravenous bisphosphonates
. High-dose NSAIDs
. Systemic corticosteroids
. Methotrexate
. Recombinant human growth hormone

Correct Answer & Explanation

. Systemic corticosteroids

Explanation

Systemic corticosteroids are the mainstay of medical treatment for the severe bone pain associated with Camurati-Engelmann disease. They decrease bone turnover, reduce pain, and can improve the characteristic waddling gait.

Question 14806

Topic: 1. General Principles & Basic Science
Which of the following mucopolysaccharidoses (MPS) is characterized by severe, progressive intellectual disability and profound central nervous system deterioration, but relatively mild somatic and orthopedic manifestations?
. MPS I (Hurler)
. MPS II (Hunter)
. MPS III (Sanfilippo)
. MPS IV (Morquio)
. MPS VI (Maroteaux-Lamy)

Correct Answer & Explanation

. MPS III (Sanfilippo)

Explanation

Sanfilippo syndrome (MPS III) primarily affects the central nervous system, leading to severe behavioral issues and cognitive decline. Somatic features such as dwarfism, skeletal dysplasias, and joint stiffness are much milder compared to other MPS types.

Question 14807

Topic: 1. General Principles & Basic Science

Which of the following enzyme deficiencies differentiates Morquio A syndrome from Morquio B syndrome?

. Morquio A is deficient in galactose-6-sulfatase; Morquio B is deficient in beta-galactosidase
. Morquio A is deficient in beta-galactosidase; Morquio B is deficient in galactose-6-sulfatase
. Morquio A is deficient in alpha-L-iduronidase; Morquio B is deficient in iduronate-2-sulfatase
. Morquio A is deficient in arylsulfatase B; Morquio B is deficient in beta-glucuronidase
. Morquio A is deficient in heparan N-sulfatase; Morquio B is deficient in alpha-N-acetylglucosaminidase

Correct Answer & Explanation

. Morquio A is deficient in galactose-6-sulfatase; Morquio B is deficient in beta-galactosidase

Explanation

Morquio A (MPS IVA) is caused by a deficiency in galactose-6-sulfatase, while the much rarer Morquio B (MPS IVB) is caused by a deficiency in beta-galactosidase. Both result in the inability to degrade keratan sulfate, leading to similar skeletal manifestations.

Question 14808

Topic: 1. General Principles & Basic Science

Which of the following clinical or radiographic features best distinguishes Ribbing disease from Camurati-Engelmann disease (Progressive Diaphyseal Dysplasia)?

. Ribbing disease typically presents with asymmetric or unilateral diaphyseal sclerosis in adults
. Ribbing disease is inherited in an X-linked recessive pattern
. Ribbing disease primarily affects the epiphyses rather than the diaphyses
. Ribbing disease causes severe intellectual disability
. Ribbing disease is characterized by extreme ligamentous laxity

Correct Answer & Explanation

. Ribbing disease typically presents with asymmetric or unilateral diaphyseal sclerosis in adults

Explanation

Ribbing disease (multiple diaphyseal sclerosis) closely resembles Camurati-Engelmann disease radiographically but usually presents after puberty with unilateral or asymmetric diaphyseal sclerosis. Camurati-Engelmann disease presents in childhood with symmetric, bilateral involvement.

Question 14809

Topic: 1. General Principles & Basic Science

When evaluating a patient with a known mucopolysaccharidosis, which clinical feature reliably helps distinguish Morquio syndrome (MPS IV) from Hurler syndrome (MPS I)?

. Presence of corneal clouding in Morquio syndrome
. Normal intelligence in Morquio syndrome
. Absence of skeletal dysplasia in Morquio syndrome
. X-linked inheritance pattern in Morquio syndrome
. Presence of hepatosplenomegaly in Morquio syndrome

Correct Answer & Explanation

. Normal intelligence in Morquio syndrome

Explanation

Patients with Morquio syndrome (MPS IV) typically have preserved, normal intelligence, despite profound skeletal dysplasias. In contrast, Hurler syndrome (MPS I) is characterized by progressive and severe cognitive decline.

Question 14810

Topic: 1. General Principles & Basic Science

A 4-year-old boy presents with progressive joint stiffness, coarse facial features, and hepatosplenomegaly. His maternal uncle had a similar presentation and passed away in his twenties. There is no corneal clouding. Which of the following is the most likely deficient enzyme?

. Alpha-L-iduronidase
. Iduronate-2-sulfatase
. Galactose-6-sulfatase
. Arylsulfatase B
. Heparan N-sulfatase

Correct Answer & Explanation

. Iduronate-2-sulfatase

Explanation

Hunter syndrome (MPS II) is characterized by X-linked recessive inheritance, explaining the maternal uncle's history, and the absence of corneal clouding. It is caused by a deficiency of iduronate-2-sulfatase.

Question 14811

Topic: Biology, Genetics & Bone Healing

A 16-year-old male presents with knee pain. Radiographs reveal an eccentric, lytic lesion with a sclerotic margin in the proximal tibial metaphysis.

Which of the following is the hallmark histological feature of this lesion?

. Chicken-wire calcification surrounding chondrocytes
. Stellate cells in a myxoid background with giant cells clustering at the lobule periphery
. Sheets of uniform small round blue cells with Homer-Wright rosettes
. Prominent osteoblastic rimming around irregular osteoid trabeculae
. Biphasic spindle cells with a herringbone pattern

Correct Answer & Explanation

. Stellate cells in a myxoid background with giant cells clustering at the lobule periphery

Explanation

Chondromyxoid fibroma exhibits a lobular pattern of stellate or spindle-shaped cells within a myxoid and chondroid background. The periphery of these lobules is highly cellular and typically contains osteoclast-like giant cells.

Question 14812

Topic: Biology, Genetics & Bone Healing

A 12-year-old girl with a known TGFB1 mutation presents with severe bilateral leg pain, muscle weakness, and a waddling gait.

Radiographs confirm progressive diaphyseal dysplasia (Camurati-Engelmann disease). Which pharmacological treatment is considered first-line to improve her symptoms and walking tolerance?

. Bisphosphonates
. Corticosteroids
. Nonsteroidal anti-inflammatory drugs (NSAIDs)
. Denosumab
. Methotrexate

Correct Answer & Explanation

. Corticosteroids

Explanation

Corticosteroids are the mainstay of medical treatment for symptomatic Camurati-Engelmann disease. They effectively relieve bone pain, improve muscle strength, and increase exercise tolerance.

Question 14813

Topic: 1. General Principles & Basic Science
A 7-year-old boy presents with profound intellectual disability, severe hyperactivity, and speech delay. Physical examination reveals mild coarse facial features but minimal skeletal abnormalities (mild dysostosis multiplex). He lacks corneal clouding. Which of the following mucopolysaccharidoses is the most likely diagnosis?
. MPS I (Hurler)
. MPS II (Hunter)
. MPS III (Sanfilippo)
. MPS IV (Morquio)
. MPS VI (Maroteaux-Lamy)

Correct Answer & Explanation

. MPS III (Sanfilippo)

Explanation

Sanfilippo syndrome (MPS III) is characterized by severe central nervous system degeneration (profound mental retardation and hyperactivity) with relatively mild somatic and skeletal features compared to other MPS disorders.

Question 14814

Topic: 1. General Principles & Basic Science

A 10-year-old girl with normal intelligence presents with severe corneal clouding, heart valve abnormalities, and joint stiffness.

Radiographs demonstrate classic dysostosis multiplex. Laboratory testing reveals an accumulation of dermatan sulfate only. Which enzyme is deficient?

. Alpha-L-iduronidase
. Iduronate-2-sulfatase
. Arylsulfatase B
. Heparan N-sulfatase
. Galactose-6-sulfatase

Correct Answer & Explanation

. Arylsulfatase B

Explanation

Maroteaux-Lamy syndrome (MPS VI) is characterized by severe skeletal changes, corneal clouding, and preserved intelligence. It is caused by a deficiency in arylsulfatase B, leading solely to dermatan sulfate accumulation.

Question 14815

Topic: Biology, Genetics & Bone Healing

A 14-year-old boy presents for evaluation of frequent shoulder dislocations. Examination reveals he can touch his shoulders together in the midline. Dental examination shows delayed eruption of secondary teeth. The underlying mutation involves a transcription factor essential for which of the following cellular processes?

. Chondrocyte proliferation in the resting zone
. Osteoclast attachment via integrins
. Osteoblast differentiation and intramembranous ossification
. Type II collagen synthesis in the articular matrix
. Sulfate transport in cartilage matrix

Correct Answer & Explanation

. Osteoblast differentiation and intramembranous ossification

Explanation

The patient has cleidocranial dysplasia, caused by a mutation in RUNX2 (CBFA1). RUNX2 is a master transcription factor required for osteoblast differentiation and is crucial for intramembranous ossification (clavicles, cranium).

Question 14816

Topic: Biology, Genetics & Bone Healing

A 9-year-old child presents with severe leg pain, waddling gait, and profound muscle weakness. Radiographs demonstrate bilateral symmetric cortical thickening of the long bone diaphyses with sparing of the epiphyses and metaphyses.

Which of the following medications is considered first-line for relieving symptoms and improving strength in this condition?

. Bisphosphonates
. Corticosteroids
. Indomethacin
. Methotrexate
. Denosumab

Correct Answer & Explanation

. Corticosteroids

Explanation

This patient has Progressive Diaphyseal Dysplasia (Camurati-Engelmann disease), caused by a TGF-beta-1 mutation. Systemic corticosteroids are the first-line treatment as they successfully relieve bone pain and improve muscle strength.

Question 14817

Topic: 1. General Principles & Basic Science

A 12-year-old boy presents with profound bilateral leg pain and fatigue. Radiographs show pronounced cortical thickening of the bilateral femoral diaphyses with sparing of the epiphyses and metaphyses.

What is the mode of inheritance for this disorder?

. Autosomal recessive
. X-linked recessive
. Autosomal dominant
. Mitochondrial
. X-linked dominant

Correct Answer & Explanation

. Autosomal dominant

Explanation

Progressive diaphyseal dysplasia (Camurati-Engelmann disease) is inherited in an autosomal dominant pattern. It is caused by mutations in the TGF-beta-1 gene, leading to excessive bone formation in the long bone diaphyses.

Question 14818

Topic: 1. General Principles & Basic Science

A 7-year-old girl is evaluated for severe short stature, coarse facial features, corneal clouding, and joint contractures. Despite these severe somatic manifestations, her intelligence is completely normal. What is the deficient enzyme in this patient's condition?

. Alpha-L-iduronidase
. Iduronate-2-sulfatase
. Heparan N-sulfatase
. Galactosamine-6-sulfatase
. Arylsulfatase B

Correct Answer & Explanation

. Arylsulfatase B

Explanation

This presentation describes Maroteaux-Lamy syndrome (MPS VI), which is characterized by normal intelligence but severe somatic features including corneal clouding. It is caused by a deficiency in Arylsulfatase B.

Question 14819

Topic: Biology, Genetics & Bone Healing

A 24-year-old male presents with a dull ache in his proximal leg. Radiographs demonstrate an eccentric, sharply circumscribed lytic lesion in the proximal tibial metaphysis with a sclerotic margin.

Biopsy demonstrates a lobular arrangement of spindle or stellate cells in an abundant myxoid background, with osteoclast-like giant cells at the lobule periphery. What is the most appropriate definitive management for this lesion?

. Simple intralesional curettage and bone grafting
. Extended intralesional curettage with high-speed burring and a local adjuvant
. Wide en bloc resection and endoprosthetic reconstruction
. Neoadjuvant chemotherapy followed by wide resection
. Observation with serial plain radiographs

Correct Answer & Explanation

. Extended intralesional curettage with high-speed burring and a local adjuvant

Explanation

The clinical, radiographic, and histologic findings are diagnostic of a chondromyxoid fibroma. Due to a recurrence rate of up to 25% with simple curettage, the standard of care is extended intralesional curettage using a high-speed burr and local adjuvants (e.g., phenol, argon beam), followed by bone grafting or cementing.

Question 14820

Topic: 1. General Principles & Basic Science

A 12-year-old boy presents with aching leg pain, severe fatigue, and a waddling gait. Radiographs demonstrate symmetrical cortical thickening of the bilateral femoral and tibial diaphyses, notably sparing the epiphyses.

Which of the following medical treatments has been shown to be most effective in alleviating pain and improving physical function in this condition?

. Intravenous bisphosphonates
. Systemic corticosteroids
. High-dose NSAIDs (Indomethacin)
. Methotrexate
. Recombinant enzyme replacement therapy

Correct Answer & Explanation

. Systemic corticosteroids

Explanation

Progressive diaphyseal dysplasia (Camurati-Engelmann disease) is caused by a TGF-beta 1 mutation. Systemic corticosteroids are the mainstay of medical treatment, effectively reducing pain, decreasing fatigue, and improving gait.

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