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1. General Principles & Basic Science MCQs

Practice Set 766 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 15301

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman is scheduled for a total hip arthroplasty due to severe osteoarthritis secondary to Paget's disease. Her alkaline phosphatase is significantly elevated. Which of the following preoperative interventions is most appropriate to minimize surgical complications?

. Preoperative administration of intravenous bisphosphonates
. Prophylactic internal fixation of the contralateral femur
. Administration of high-dose corticosteroids 48 hours prior to surgery
. Empiric preoperative embolization of the femoral artery
. Delaying surgery until serum calcium normalizes

Correct Answer & Explanation

. Preoperative administration of intravenous bisphosphonates

Explanation

Preoperative treatment with bisphosphonates is recommended in patients with active Paget's disease (indicated by high alkaline phosphatase) to reduce disease activity and significantly decrease intraoperative blood loss from hypervascular pagetic bone.

Question 15302

Topic: Biology, Genetics & Bone Healing

Which of the following classic histological findings is the hallmark of the mixed phase of Paget's disease?

. Woven bone with empty lacunae
. A 'mosaic' pattern of lamellar bone with prominent, haphazard cement lines
. Sheets of plasma cells with clock-face nuclei
. Bands of unmineralized osteoid surrounding calcified bone
. Multinucleated giant cells in a background of mononuclear stromal cells

Correct Answer & Explanation

. A 'mosaic' pattern of lamellar bone with prominent, haphazard cement lines

Explanation

The mixed phase of Paget's disease is characterized by a high rate of bone turnover, histologically appearing as a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone with prominent, haphazard cement lines.

Question 15303

Topic: Biology, Genetics & Bone Healing

A patient with widespread Paget's disease develops progressive shortness of breath and bilateral lower extremity edema. Echocardiography reveals a normal ejection fraction but a markedly elevated cardiac output. What is the pathophysiological mechanism of this complication?

. Cor pulmonale due to thoracic spine kyphoscoliosis
. High-output cardiac failure secondary to multiple arteriovenous shunts within the pagetic bone
. Secondary amyloidosis affecting the myocardium
. Aortic root dilation from associated connective tissue defects
. Constrictive pericarditis from paramyxovirus infection

Correct Answer & Explanation

. High-output cardiac failure secondary to multiple arteriovenous shunts within the pagetic bone

Explanation

Extensive Paget's disease (involving >15% of the skeleton) can cause high-output heart failure due to increased metabolic demand and the formation of numerous microscopic arteriovenous shunts within the hypervascular pagetic bone.

Question 15304

Topic: Biology, Genetics & Bone Healing

A 3-month-old infant presents with failure to thrive, hepatosplenomegaly, and generalized increased bone density on radiographs. The defect responsible for this condition primarily affects which of the following cellular processes?

. Osteoblast differentiation via Wnt/beta-catenin signaling
. Osteoclast ability to create an acidic microenvironment for bone resorption
. Chondrocyte proliferation in the resting zone
. Collagen type I triple helix formation
. Mineralization of osteoid by alkaline phosphatase

Correct Answer & Explanation

. Osteoclast ability to create an acidic microenvironment for bone resorption

Explanation

The patient has malignant infantile osteopetrosis, characterized by defective osteoclast function (often due to TCIRG1 or ClCN7 mutations). The osteoclasts fail to form a ruffled border and cannot secrete the acid and enzymes necessary to resorb bone.

Question 15305

Topic: Biology, Genetics & Bone Healing

Review the provided radiograph.

This characteristic 'bone-within-a-bone' appearance is pathognomonic for a condition caused by a defect in cells derived from which of the following lineages?

. Mesenchymal stem cell
. Hematopoietic macrophage/monocyte lineage
. Neural crest
. Endodermal progenitor
. Ectodermal placode

Correct Answer & Explanation

. Hematopoietic macrophage/monocyte lineage

Explanation

The radiograph demonstrates the 'bone-within-a-bone' appearance of osteopetrosis. This disease is caused by defective osteoclasts, which differentiate from the hematopoietic macrophage/monocyte lineage, not mesenchymal stem cells.

Question 15306

Topic: Biology, Genetics & Bone Healing

A 4-year-old child with a known diagnosis of malignant infantile osteopetrosis is being considered for definitive treatment. Which of the following is the only potential curative therapy for the underlying bone pathology in this patient?

. Lifelong bisphosphonate therapy
. Parathyroid hormone (Teriparatide) daily injections
. Hematopoietic stem cell transplantation
. Autologous mesenchymal stem cell infusion
. High-dose calcitriol supplementation

Correct Answer & Explanation

. Hematopoietic stem cell transplantation

Explanation

Hematopoietic stem cell transplantation (HSCT) is the only curative treatment for malignant infantile osteopetrosis. It replaces the defective hematopoietic precursors, allowing for the development of normally functioning osteoclasts.

Question 15307

Topic: Biology, Genetics & Bone Healing

A patient with Paget's disease is treated with a nitrogen-containing bisphosphonate (e.g., Alendronate). By which intracellular mechanism does this medication primarily inhibit osteoclast function?

. Binding to the RANK ligand, preventing its interaction with RANK
. Inhibition of the enzyme farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway
. Direct inhibition of Carbonic Anhydrase II
. Activation of the calcium-sensing receptor (CaSR) on the osteoclast membrane
. Inhibition of cathepsin K

Correct Answer & Explanation

. Inhibition of the enzyme farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates work by inhibiting farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This prevents the prenylation of small GTPase proteins (like Ras and Rho) required for osteoclast survival and ruffled border formation.

Question 15308

Topic: Biology, Genetics & Bone Healing
A patient with Autosomal Recessive Osteopetrosis (ARO) is found to have a concurrent diagnosis of renal tubular acidosis and bilateral cerebral calcifications. A deficiency in which of the following enzymes is responsible for this specific triad?
. Tissue-nonspecific alkaline phosphatase (TNSALP)
. Cathepsin K
. Carbonic Anhydrase II
. Tartrate-resistant acid phosphatase (TRAP)
. Glucocerebrosidase

Correct Answer & Explanation

. Carbonic Anhydrase II

Explanation

The triad of osteopetrosis, renal tubular acidosis, and cerebral calcifications is characteristic of Carbonic Anhydrase II (CA II) deficiency. CA II is required by osteoclasts to generate protons for bone resorption and by renal tubules for acid-base regulation.

Question 15309

Topic: Biology, Genetics & Bone Healing

In the evaluation of a patient with suspected Paget's disease of bone, which of the following serum laboratory profiles is most classic for an active, uncomplicated disease state?

. Elevated calcium, low phosphorus, elevated alkaline phosphatase
. Normal calcium, normal phosphorus, markedly elevated alkaline phosphatase
. Low calcium, low phosphorus, elevated alkaline phosphatase
. Normal calcium, elevated phosphorus, normal alkaline phosphatase
. Elevated calcium, normal phosphorus, normal alkaline phosphatase

Correct Answer & Explanation

. Normal calcium, normal phosphorus, markedly elevated alkaline phosphatase

Explanation

In uncomplicated, active Paget's disease, serum calcium and phosphorus levels are typically normal, while serum alkaline phosphatase (a marker of bone formation) and urinary hydroxyproline (a marker of bone resorption) are elevated due to high bone turnover.

Question 15310

Topic: 1. General Principles & Basic Science
Which of the following cranial nerve complications is most classically associated with severe infantile osteopetrosis?
. Trigeminal neuralgia (CN V)
. Bell's palsy (CN VII)
. Blindness and deafness (CN II and VIII)
. Vocal cord paralysis (CN X)
. Tongue deviation (CN XII)

Correct Answer & Explanation

. Blindness and deafness (CN II and VIII)

Explanation

In infantile osteopetrosis, the failure of bone remodeling leads to narrowing of the cranial neural foramina. This classically results in compression of the optic (CN II) and vestibulocochlear (CN VIII) nerves, causing blindness and deafness.

Question 15311

Topic: Biology, Genetics & Bone Healing
A 55-year-old female with Paget's disease presents with increasing bowing of her tibia and local warmth over the bone. Radiographs show the 'blade of grass' sign. Which cellular sequence accurately describes the pathological progression of her disease?
. Osteosclerotic phase → Mixed phase → Osteolytic phase
. Osteolytic phase → Mixed phase → Osteosclerotic phase
. Mixed phase → Osteolytic phase → Osteosclerotic phase
. Osteosclerotic phase → Osteolytic phase → Mixed phase
. Osteolytic phase → Osteosclerotic phase → Mixed phase

Correct Answer & Explanation

. Osteolytic phase → Mixed phase → Osteosclerotic phase

Explanation

Paget's disease progresses through three phases: an initial intense osteolytic phase (driven by overactive osteoclasts, showing a 'blade of grass' or 'V-shaped' lytic leading edge), followed by a mixed lytic/sclerotic phase, and finally an inactive, dense osteosclerotic phase.

Question 15312

Topic: Biology, Genetics & Bone Healing

Infantile malignant osteopetrosis is most commonly associated with a mutation in which of the following genes, resulting in defective osteoclast function?

. TCIRG1
. CLCN7
. CAII
. OSTM1
. TRPS1

Correct Answer & Explanation

. TCIRG1

Explanation

TCIRG1 mutations account for greater than 50% of infantile malignant osteopetrosis cases. This gene encodes a subunit of the vacuolar proton pump required for osteoclast-mediated bone resorption.

Question 15313

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with symptomatic Paget's disease is treated with a nitrogen-containing bisphosphonate. What is the primary molecular target of this medication?

. Carbonic anhydrase II
. Farnesyl pyrophosphate synthase
. Cathepsin K
. RANK ligand
. Vacuolar H+-ATPase

Correct Answer & Explanation

. Farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates, such as zoledronic acid, inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This disrupts osteoclast function and induces osteoclast apoptosis.

Question 15314

Topic: Biology, Genetics & Bone Healing

Histological evaluation of a bone biopsy from a patient with Paget's disease shows a mosaic pattern of lamellar bone with prominent cement lines. This represents which phase of the disease?

. Lytic phase
. Mixed phase
. Sclerotic phase
. Malignant transformation phase
. Osteoclastic phase

Correct Answer & Explanation

. Sclerotic phase

Explanation

The sclerotic (or late/inactive) phase of Paget's disease is characterized by a mosaic or jigsaw-puzzle pattern of lamellar bone. This is due to haphazard cement lines left by highly disorganized bone remodeling.

Question 15315

Topic: 1. General Principles & Basic Science

A 65-year-old man with Paget's disease affecting his right hip requires a total hip arthroplasty for severe secondary osteoarthritis. Which preoperative intervention is most appropriate to minimize intraoperative blood loss?

. Preoperative embolization of the internal iliac artery
. Administration of zoledronic acid 2 months prior to surgery
. Administration of denosumab 1 week prior to surgery
. Prophylactic radiation therapy
. Preoperative tranexamic acid infusion only

Correct Answer & Explanation

. Administration of zoledronic acid 2 months prior to surgery

Explanation

Preoperative administration of a bisphosphonate reduces Pagetic disease activity and dramatically decreases bone vascularity. This significantly minimizes intraoperative blood loss during arthroplasty.

Question 15316

Topic: Biology, Genetics & Bone Healing

Which of the following is the only potentially curative treatment for infantile malignant osteopetrosis?

. High-dose calcitriol
. Interferon gamma-1b
. Hematopoietic stem cell transplantation
. Bisphosphonate therapy
. Recombinant human parathyroid hormone

Correct Answer & Explanation

. Hematopoietic stem cell transplantation

Explanation

Hematopoietic stem cell transplantation (HSCT) is the only curative treatment for infantile malignant osteopetrosis. It provides a new source of hematopoietic progenitors that can differentiate into functional osteoclasts.

Question 15317

Topic: Biology, Genetics & Bone Healing

A 70-year-old man complains of increasing hat size and hearing loss. A skull radiograph is obtained.

Which of the following classic radiographic signs is most likely to be seen in the early stage of this cranial disease?

. Cotton wool appearance
. Osteoporosis circumscripta
. Salt and pepper skull
. Hair-on-end appearance
. Punched-out lytic lesions

Correct Answer & Explanation

. Osteoporosis circumscripta

Explanation

Osteoporosis circumscripta is the classic large, well-defined lytic lesion seen in the early (osteoclastic) phase of Paget's disease in the skull. The 'cotton wool' appearance occurs much later during the mixed and sclerotic phases.

Question 15318

Topic: Biology, Genetics & Bone Healing

What are the typical serum calcium, phosphorus, and alkaline phosphatase levels in a patient with adult-onset (autosomal dominant) osteopetrosis?

. High calcium, low phosphorus, high alkaline phosphatase
. Normal calcium, normal phosphorus, normal alkaline phosphatase
. Low calcium, high phosphorus, low alkaline phosphatase
. Normal calcium, normal phosphorus, highly elevated alkaline phosphatase
. Low calcium, low phosphorus, high alkaline phosphatase

Correct Answer & Explanation

. Normal calcium, normal phosphorus, normal alkaline phosphatase

Explanation

In adult-onset osteopetrosis, routine serum levels of calcium, phosphorus, and alkaline phosphatase are typically normal. This distinguishes it from conditions like Paget's disease or rickets where these markers are frequently abnormal.

Question 15319

Topic: Biology, Genetics & Bone Healing
The sensorineural hearing loss commonly seen in patients with Paget's disease of the skull is most directly attributed to:
. Otosclerosis of the stapes footplate
. Microvascular ischemia of the cochlea
. Cranial nerve VIII entrapment in the internal auditory canal
. Changes in bone density affecting cochlear mechanics and nerve compression
. Direct toxicity of bisphosphonate therapy

Correct Answer & Explanation

. Changes in bone density affecting cochlear mechanics and nerve compression

Explanation

Hearing loss in Paget's disease is typically mixed. Sensorineural loss results from Pagetic involvement of the temporal bone altering cochlear mechanics and microanatomy, while conductive loss is due to ossicular chain involvement.

Question 15320

Topic: Biology, Genetics & Bone Healing

The TRPS1 gene encodes a zinc-finger transcription factor. Its mutation primarily affects the development of which of the following tissue types?

. Articular hyaline cartilage
. Growth plate chondrocytes and perichondrium
. Osteoblasts of the diaphyseal cortex
. Hematopoietic stem cells
. Osteoclasts of the primary spongiosa

Correct Answer & Explanation

. Growth plate chondrocytes and perichondrium

Explanation

The TRPS1 transcription factor is heavily expressed in the growth plate and perichondrium. Mutations disrupt normal chondrocyte proliferation and apoptosis, leading to the characteristic cone-shaped epiphyses.

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