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1. General Principles & Basic Science MCQs

Practice Set 749 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 14961

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with severe bowing of the lower extremities. Labs show normal calcium, low phosphorus, and elevated alkaline phosphatase. Genetic testing reveals a PHEX gene mutation. Which of the following is the primary mechanism of this disease?

. Decreased renal production of 1,25-OH vitamin D
. Increased renal phosphate excretion due to elevated FGF-23
. Impaired osteoclast function due to TCIRG1 mutation
. Defective type I collagen synthesis
. Autoimmune destruction of the parathyroid gland

Correct Answer & Explanation

. Increased renal phosphate excretion due to elevated FGF-23

Explanation

PHEX mutations lead to decreased degradation of FGF-23 in X-linked hypophosphatemic rickets. Elevated FGF-23 causes increased renal phosphate excretion and inhibits 1-alpha-hydroxylase, leading to severe hypophosphatemia and rickets.

Question 14962

Topic: Biology, Genetics & Bone Healing

A 3-year-old girl is diagnosed with oligoarticular Juvenile Idiopathic Arthritis (JIA) affecting her right knee. She has a positive ANA and negative Rheumatoid Factor. What is the most critical screening protocol she must undergo?

. Annual echocardiograms to screen for pericarditis
. Routine slit-lamp examinations every 3-4 months to screen for asymptomatic uveitis
. Monthly liver function tests
. Annual DEXA scans to monitor for osteopenia
. Routine pulmonary function testing for interstitial lung disease

Correct Answer & Explanation

. Routine slit-lamp examinations every 3-4 months to screen for asymptomatic uveitis

Explanation

Young girls with ANA-positive oligoarticular JIA are at the highest risk for asymptomatic anterior uveitis. They require frequent slit-lamp examinations (every 3-4 months) by an ophthalmologist to prevent permanent vision loss.

Question 14963

Topic: Biology, Genetics & Bone Healing

A 7-year-old boy presents for orthopedic evaluation. He is remarkably able to bring his shoulders together anteriorly in the midline. Radiographs reveal absent clavicles and delayed closure of the cranial sutures. A mutation in which of the following transcription factors is responsible?

. SOX9
. RUNX2 (CBFA1)
. GLI3
. HOXD13
. PAX3

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is an autosomal dominant condition caused by mutations in the RUNX2 (CBFA1) gene, an essential transcription factor for osteoblast differentiation. It is characterized by absent or hypoplastic clavicles and delayed cranial suture closure.

Question 14964

Topic: 1. General Principles & Basic Science

A 7-year-old boy with a history of systemic Juvenile Idiopathic Arthritis (JIA) presents to the emergency department with high continuous fever, hepatosplenomegaly, purpura, and abrupt onset of severe lethargy. Labs reveal falling ESR, extreme hyperferritinemia, and thrombocytopenia. What is the most likely life-threatening complication occurring?

. Septic shock
. Macrophage Activation Syndrome (MAS)
. Acute rheumatic fever
. Toxic shock syndrome
. Secondary leukemia

Correct Answer & Explanation

. Macrophage Activation Syndrome (MAS)

Explanation

Macrophage Activation Syndrome (MAS) is a severe, life-threatening complication of systemic JIA. It is characterized by sudden fever, hepatosplenomegaly, cytopenias, a paradoxically falling ESR, and severely elevated ferritin, requiring immediate high-dose corticosteroids.

Question 14965

Topic: Biology, Genetics & Bone Healing

A 24-month-old toddler presents with a waddling gait and bowing of the legs. Radiographs show widening and cupping of the distal femoral physes, as well as radiolucent bands perpendicular to the cortex in the medial femoral neck. Which of the following is the most likely diagnosis for the radiolucent bands?

. Stress fractures
. Looser zones (pseudofractures)
. Non-ossifying fibromas
. Harris growth arrest lines
. Enchondromas

Correct Answer & Explanation

. Looser zones (pseudofractures)

Explanation

Looser zones, or pseudofractures, are wide transverse radiolucencies traversing part of the bone, representing accumulations of unmineralized osteoid. They are a classic radiographic hallmark of osteomalacia and severe rickets.

Question 14966

Topic: Infection, Pharmacology & VTE

A 9-year-old boy is admitted with severe, multifocal MRSA osteomyelitis and an associated deep vein thrombosis (DVT) of the affected extremity. The severity of this infection and the development of DVT are most strongly associated with which bacterial virulence factor?

. Panton-Valentine leukocidin (PVL)
. Toxic shock syndrome toxin-1 (TSST-1)
. Exfoliative toxin A
. Protein A
. Alpha-hemolysin

Correct Answer & Explanation

. Panton-Valentine leukocidin (PVL)

Explanation

Panton-Valentine leukocidin (PVL) is a cytotoxin produced by community-acquired MRSA strains that destroys leukocytes and causes severe tissue necrosis. PVL-positive strains are strongly associated with multifocal disease, aggressive osteomyelitis, and adjacent deep vein thrombosis.

Question 14967

Topic: Biology, Genetics & Bone Healing

A 3-year-old child with frequent fractures, blue sclerae, and dentinogenesis imperfecta is started on intravenous bisphosphonate therapy (pamidronate). What is the primary cellular mechanism of action of this medication in treating this disease?

. Stimulates osteoblast differentiation
. Inhibits osteoclast activity by inducing apoptosis
. Promotes type 1 collagen cross-linking
. Stimulates renal production of 1,25-OH vitamin D
. Neutralizes the mutant COL1A1 protein

Correct Answer & Explanation

. Inhibits osteoclast activity by inducing apoptosis

Explanation

Bisphosphonates are analogues of inorganic pyrophosphate that bind to hydroxyapatite and are ingested by osteoclasts. They inhibit osteoclastic bone resorption by disrupting the mevalonate pathway and inducing osteoclast apoptosis, thereby increasing bone mineral density in Osteogenesis Imperfecta.

Question 14968

Topic: 1. General Principles & Basic Science

A 10-year-old boy presents with progressive knee pain and short stature. Radiographs demonstrate delayed ossification of the capital femoral epiphyses and irregular secondary ossification centers. A lateral radiograph of the knee reveals a pathognomonic finding. What is this finding?

. Double-layered patella
. Patella alta
. Bipartite patella
. Patella baja
. Hypoplastic fragmented patella

Correct Answer & Explanation

. Double-layered patella

Explanation

Multiple epiphyseal dysplasia (MED) is characterized by delayed ossification of multiple epiphyses. A double-layered patella on a lateral knee radiograph is considered a pathognomonic finding for this dysplasia.

Question 14969

Topic: Biology, Genetics & Bone Healing
A 3-year-old child presents with progressive varus bowing of the lower extremities. Laboratory studies reveal a normal serum calcium, significantly decreased serum phosphate, normal PTH, and elevated alkaline phosphatase. What is the primary pathophysiologic mechanism of this disease?
. Decreased intestinal calcium absorption
. Inability to convert 25-OH Vitamin D to 1,25-OH Vitamin D
. Mutations in the calcium-sensing receptor (CaSR)
. Deficiency in tissue nonspecific alkaline phosphatase (TNSALP)
. Decreased renal tubular reabsorption of phosphate due to excess FGF23

Correct Answer & Explanation

. Decreased renal tubular reabsorption of phosphate due to excess FGF23

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX gene mutation that leads to excess FGF23 production. FGF23 decreases renal tubular reabsorption of phosphate, resulting in profound hypophosphatemia and secondary rickets.

Question 14970

Topic: Biology, Genetics & Bone Healing

A neonate is noted to have a large anterior fontanelle, delayed closure of cranial sutures, and unusual mobility of the shoulders allowing them to be opposed anteriorly. A mutation in which of the following transcription factors is responsible for this condition?

. SOX9
. RUNX2 (CBFA1)
. GLI3
. SHOX
. HOXD13

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is caused by an autosomal dominant mutation in the RUNX2 (CBFA1) gene, which regulates osteoblast differentiation. This leads to defective intramembranous ossification, characterized by absent/hypoplastic clavicles and delayed fontanelle closure.

Question 14971

Topic: Biology, Genetics & Bone Healing

A 2-year-old child recently immigrated to the US presents with irritability, delayed walking, and widening of the wrists. Radiographs show cupping and fraying of the metaphyseal-physeal junctions. Which of the following laboratory profiles confirms the diagnosis of nutritional rickets?

. Decreased 25-OH Vitamin D, Increased PTH, Decreased Phosphate
. Normal 25-OH Vitamin D, Increased PTH, Increased Phosphate
. Normal 25-OH Vitamin D, Normal PTH, Decreased Phosphate
. Increased 1,25-OH Vitamin D, Decreased PTH, Normal Phosphate
. Decreased 25-OH Vitamin D, Decreased PTH, Decreased Calcium

Correct Answer & Explanation

. Decreased 25-OH Vitamin D, Increased PTH, Decreased Phosphate

Explanation

Nutritional rickets results from Vitamin D deficiency, leading to decreased calcium absorption. This triggers secondary hyperparathyroidism, which increases serum calcium toward normal but causes profound renal phosphate wasting.

Question 14972

Topic: Biology, Genetics & Bone Healing

A 45-year-old male with end-stage renal disease on hemodialysis presents with diffuse bone pain. Radiographs demonstrate 'rugger jersey' spine and osteopenia. What is the primary driving mechanism for his metabolic bone disease?

. Primary hyperparathyroidism due to an adenoma
. Hypophosphatemia inducing osteomalacia
. Hyperphosphatemia causing secondary hyperparathyroidism
. Excessive production of 1,25-OH Vitamin D
. Aluminum toxicity impairing osteoid mineralization

Correct Answer & Explanation

. Hyperphosphatemia causing secondary hyperparathyroidism

Explanation

In renal osteodystrophy, failing kidneys cannot excrete phosphate or adequately synthesize 1,25-dihydroxyvitamin D. The resulting hyperphosphatemia and hypocalcemia drive severe secondary hyperparathyroidism, leading to high-turnover bone disease.

Question 14973

Topic: Infection, Pharmacology & VTE
A 2-year-old child presents with a limp, fever, and a swollen knee. Aspiration yields purulent synovial fluid with a WBC of 65,000. Standard aerobic and anaerobic cultures on solid media are negative at 48 hours. What technique would have best optimized the isolation of the most likely responsible organism?
. Extended incubation of anaerobic cultures for 14 days
. Addition of acid-fast bacilli (AFB) stains
. Direct inoculation of synovial fluid into BACTEC blood culture vials
. Polymerase chain reaction (PCR) targeting Neisseria gonorrhoeae
. Culturing the fluid specifically on MacConkey agar

Correct Answer & Explanation

. Direct inoculation of synovial fluid into BACTEC blood culture vials

Explanation

Kingella kingae is a highly fastidious organism and the most common cause of septic arthritis in children under 4 years old. Isolation is significantly enhanced by inoculating synovial fluid directly into aerobic BACTEC blood culture vials.

Question 14974

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis frequently causes chronic prosthetic joint infections due to its ability to form a robust biofilm. Which specific structural component produced by this bacteria is primarily responsible for adherence and biofilm architecture?

. Protein A
. Polysaccharide intercellular adhesin (PIA)
. Panton-Valentine leukocidin (PVL)
. Alpha-toxin
. Toxic shock syndrome toxin-1 (TSST-1)

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

S. epidermidis secures itself to orthopaedic implants via a biofilm composed of an exopolysaccharide matrix. The critical structural component of this glycocalyx is polysaccharide intercellular adhesin (PIA).

Question 14975

Topic: 1. General Principles & Basic Science
A 55-year-old male with diabetes presents with a rapidly progressive, extremely painful, swollen, and erythematous lower extremity. You calculate a Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score. Which of the following laboratory parameters is NOT included in this score?
. C-reactive protein (CRP)
. White blood cell count (WBC)
. Hemoglobin
. Serum potassium
. Serum sodium

Correct Answer & Explanation

. Serum potassium

Explanation

The LRINEC score helps differentiate necrotizing fasciitis from severe cellulitis. Its variables include CRP, WBC, hemoglobin, sodium, creatinine, and glucose; serum potassium is not part of the score.

Question 14976

Topic: Biology, Genetics & Bone Healing

A 4-year-old female is recently diagnosed with oligoarticular Juvenile Idiopathic Arthritis. Her laboratory workup is positive for Antinuclear Antibody (ANA). Which of the following represents the most critical screening protocol for this patient?

. Echocardiogram every 6 months to monitor for pericarditis
. Ophthalmology referral for slit-lamp examinations every 3 to 4 months
. Monthly complete blood counts to check for macrophage activation syndrome
. Annual DXA scans to monitor for systemic osteoporosis
. Routine pulmonary function tests to detect interstitial lung disease

Correct Answer & Explanation

. Ophthalmology referral for slit-lamp examinations every 3 to 4 months

Explanation

Young females with ANA-positive oligoarticular JIA carry the highest risk of developing asymptomatic anterior uveitis. Routine slit-lamp examinations every 3 to 4 months are critical to prevent permanent visual impairment or blindness.

Question 14977

Topic: 1. General Principles & Basic Science

A 6-year-old boy presents with daily spiking fevers, generalized lymphadenopathy, a transient salmon-colored macular rash, and polyarthritis. Which potentially fatal hematologic complication is most uniquely associated with this specific subtype of Juvenile Idiopathic Arthritis?

. Macrophage activation syndrome
. Aplastic anemia
. Acute lymphoblastic leukemia
. Hemolytic uremic syndrome
. Thrombotic thrombocytopenic purpura

Correct Answer & Explanation

. Macrophage activation syndrome

Explanation

Systemic JIA (Still's disease) uniquely predisposes patients to Macrophage Activation Syndrome (MAS). MAS is a severe, life-threatening complication characterized by an overwhelming inflammatory cascade and multi-organ failure.

Question 14978

Topic: Biology, Genetics & Bone Healing

A 5-year-old girl with severe bowing of the lower extremities is diagnosed with X-linked hypophosphatemic rickets (XLH). Which laboratory profile is most specific to the pathophysiology of her disease?

. Elevated PTH, low calcium
. Elevated FGF23, low phosphate
. Low 1,25-dihydroxyvitamin D, normal phosphate
. Low alkaline phosphatase, high calcium
. Normal FGF23, high PTH

Correct Answer & Explanation

. Elevated FGF23, low phosphate

Explanation

XLH is caused by a PHEX gene mutation that leads to excess production of FGF23. Elevated FGF23 causes profound renal phosphate wasting, resulting in hypophosphatemia with normal serum calcium and normal PTH levels.

Question 14979

Topic: 1. General Principles & Basic Science

Which of the following patients with Juvenile Idiopathic Arthritis (JIA) requires the most frequent slit-lamp examinations due to having the highest risk for developing silent anterior uveitis?

. A 3-year-old girl with ANA-positive oligoarticular JIA
. An 8-year-old boy with RF-positive polyarticular JIA
. A 10-year-old girl with ANA-negative systemic JIA
. A 4-year-old boy with HLA-B27-positive enthesitis-related JIA
. A 12-year-old girl with ANA-negative oligoarticular JIA

Correct Answer & Explanation

. A 3-year-old girl with ANA-positive oligoarticular JIA

Explanation

The highest risk for silent, asymptomatic anterior uveitis in JIA occurs in young, female patients with oligoarticular onset who are antinuclear antibody (ANA) positive. Frequent routine screening is mandatory to prevent blindness.

Question 14980

Topic: Infection, Pharmacology & VTE
A 14-month-old presents with acute knee swelling and refusal to bear weight. Aspiration yields cloudy fluid. Routine synovial cultures on blood agar are negative at 48 hours. What is the optimal method to isolate the most likely organism in this specific age group?
. Fungal culture isolation
. Acid-fast bacilli smear and culture
. Inoculation into aerobic blood culture vials
. Lowenstein-Jensen medium plating
. Thayer-Martin agar plating

Correct Answer & Explanation

. Inoculation into aerobic blood culture vials

Explanation

Kingella kingae is a fastidious Gram-negative organism and a leading cause of septic arthritis in children under 4 years of age. It is best isolated by inoculating synovial fluid directly into BACTEC blood culture vials or via PCR testing.

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