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1. General Principles & Basic Science MCQs

Practice Set 456 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 9101

Topic: 1. General Principles & Basic Science

A patient with recurrent gout flares and multiple tophi is started on allopurinol for long-term management. What is the primary mechanism of action of this medication?

. Inhibition of microtubule assembly
. Uricosuric action at the proximal renal tubule
. Competitive inhibition of xanthine oxidase
. Recombinant uricase converting urate to allantoin
. Inhibition of cyclooxygenase-2

Correct Answer & Explanation

. Competitive inhibition of xanthine oxidase

Explanation

Allopurinol is a purine analog that competitively inhibits xanthine oxidase, the enzyme responsible for converting hypoxanthine to xanthine and xanthine to uric acid. It is the first-line urate-lowering therapy for chronic gout.

Question 9102

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size and bilateral hearing loss. Radiographs show cortical thickening and a 'cotton-wool' appearance of the skull. Which of the following best describes the primary cellular defect in this condition?

. Decreased osteoid mineralization
. Defective osteoclast carbonic anhydrase II
. Excessive proliferation of mononuclear osteoblasts
. Overactivity of giant multinucleated osteoclasts
. Deficiency of tissue nonspecific alkaline phosphatase

Correct Answer & Explanation

. Overactivity of giant multinucleated osteoclasts

Explanation

Paget's disease is primarily a disorder of osteoclast overactivity, characterized by giant, multinucleated osteoclasts. This leads to chaotic bone remodeling and the classic 'cotton-wool' appearance on skull radiographs.

Question 9103

Topic: 1. General Principles & Basic Science

A 55-year-old male presents with chronic pain and swelling in his left big toe. Radiographs demonstrate a soft tissue mass and a periarticular 'punched-out' lytic lesion with an overhanging sclerotic margin.

Joint aspiration is most likely to reveal which of the following?

. Positively birefringent rhomboid crystals
. Negatively birefringent needle-shaped crystals
. Gram-positive cocci in clusters
. Multinucleated giant cells with hemosiderin
. Non-birefringent envelope-shaped crystals

Correct Answer & Explanation

. Negatively birefringent needle-shaped crystals

Explanation

The clinical and radiographic presentation is classic for chronic tophaceous gout, characterized by 'rat-bite' erosions with overhanging margins. Aspiration will show monosodium urate crystals, which are needle-shaped and strongly negatively birefringent.

Question 9104

Topic: Biology, Genetics & Bone Healing

A 72-year-old male with known Paget's disease of the femur presents with a severe, sudden increase in thigh pain over the past month. Radiographs show a new destructive, lytic lesion with cortical breakthrough and a soft tissue mass. What is the most significant prognostic factor for this patient's new condition?

. The presence of a paramyxovirus infection
. Development of high-output heart failure
. The histologic grade of the secondary sarcoma
. Serum calcium levels
. Nearly 100% mortality within 5 years despite aggressive treatment

Correct Answer & Explanation

. Nearly 100% mortality within 5 years despite aggressive treatment

Explanation

This patient has developed a secondary osteosarcoma, a rare but lethal complication of Paget's disease (incidence <1%). Pagetic osteosarcoma is highly aggressive, with a 5-year survival rate typically less than 10-20% despite surgery and chemotherapy.

Question 9105

Topic: 1. General Principles & Basic Science

A 60-year-old male with recurrent gout attacks is started on allopurinol for chronic maintenance therapy. Which of the following best describes the primary mechanism of action of this medication?

. Inhibits microtubule polymerization
. Inhibits cyclooxygenase-2 selectively
. Inhibits xanthine oxidase
. Increases renal excretion of uric acid by inhibiting URAT1
. Recombinantly degrades uric acid to allantoin

Correct Answer & Explanation

. Inhibits xanthine oxidase

Explanation

Allopurinol is a xanthine oxidase inhibitor that decreases uric acid production by preventing the conversion of hypoxanthine to xanthine and xanthine to uric acid. Colchicine inhibits microtubule polymerization, and probenecid increases renal excretion.

Question 9106

Topic: Biology, Genetics & Bone Healing

A 68-year-old female with severe secondary osteoarthritis of the hip and active Paget's disease is scheduled for a total hip arthroplasty. Her serum alkaline phosphatase is significantly elevated. What is the most appropriate preoperative medical management to optimize her surgical outcome?

. Initiate high-dose corticosteroids 1 week prior to surgery
. Administer a course of bisphosphonates prior to surgery
. Perform preoperative embolization of the internal iliac artery
. Initiate allopurinol therapy to prevent post-operative flare
. No preoperative medical intervention is indicated

Correct Answer & Explanation

. Administer a course of bisphosphonates prior to surgery

Explanation

Preoperative treatment with bisphosphonates or calcitonin is recommended in patients with active Paget's disease before elective bone surgery like THA. This reduces osteoclast activity, thereby significantly decreasing intraoperative blood loss from the highly vascular pagetic bone.

Question 9107

Topic: Infection, Pharmacology & VTE

A 52-year-old male with a history of chronic gout on allopurinol 300mg daily presents with an acute, severely painful flare in his right knee. Synovial fluid shows negatively birefringent crystals. What is the most appropriate management of his allopurinol during this acute attack?

. Discontinue allopurinol immediately and start colchicine
. Double the allopurinol dose to rapidly lower uric acid
. Maintain the current dose of allopurinol and add an NSAID or colchicine
. Discontinue allopurinol and substitute with probenecid
. Switch allopurinol to febuxostat

Correct Answer & Explanation

. Maintain the current dose of allopurinol and add an NSAID or colchicine

Explanation

During an acute gout flare, urate-lowering therapy like allopurinol should not be discontinued or initiated, as sudden fluctuations in serum uric acid can prolong or worsen the attack. The correct approach is to maintain the current allopurinol dose and treat the acute inflammation.

Question 9108

Topic: 1. General Principles & Basic Science

A 55-year-old male presents with an acutely swollen, erythematous, and exquisitely tender first metatarsophalangeal joint. Joint aspiration is performed. What findings are expected upon polarized light microscopy of the synovial fluid?

. Positively birefringent rhomboid-shaped crystals
. Negatively birefringent needle-shaped crystals
. Non-birefringent needle-shaped crystals
. Positively birefringent envelope-shaped crystals
. Negatively birefringent rhomboid-shaped crystals

Correct Answer & Explanation

. Negatively birefringent needle-shaped crystals

Explanation

Gout is caused by monosodium urate crystals, which appear as negatively birefringent, needle-shaped crystals under polarized light microscopy. Pseudogout features positively birefringent rhomboid crystals.

Question 9109

Topic: Biology, Genetics & Bone Healing

Which of the following cellular mechanisms is considered the primary initiating event in the pathophysiology of Paget's disease of bone?

. Osteoblast hypersecretion of osteoid
. Osteoclast overactivity with viral-like inclusion bodies
. Osteocyte apoptosis leading to structural failure
. Chondrocyte hypertrophy in the epiphyseal plate
. Fibroblast proliferation within the bone marrow

Correct Answer & Explanation

. Osteoclast overactivity with viral-like inclusion bodies

Explanation

Paget's disease is primarily initiated by abnormal, hyperactive osteoclasts containing viral-like inclusion bodies, followed by compensatory, disorganized osteoblastic bone formation.

Question 9110

Topic: Infection, Pharmacology & VTE

A 60-year-old male with chronic gout currently taking allopurinol 300 mg daily presents to the clinic with an acute gout flare in his left knee. What is the most appropriate modification to his allopurinol regimen during this acute flare?

. Stop allopurinol and start indomethacin
. Continue allopurinol at the current dose and start indomethacin
. Increase the allopurinol dose to 450 mg daily
. Stop allopurinol and start probenecid
. Switch allopurinol to febuxostat immediately

Correct Answer & Explanation

. Continue allopurinol at the current dose and start indomethacin

Explanation

During an acute gout flare, existing urate-lowering therapy like allopurinol should be continued without dose alteration to prevent rapid fluctuations in uric acid. Acute flares are concurrently treated with NSAIDs, colchicine, or corticosteroids.

Question 9111

Topic: Biology, Genetics & Bone Healing

A 68-year-old male with Paget's disease of the tibia presents with worsening bone pain and an elevated serum alkaline phosphatase level. What is the first-line pharmacological treatment for this symptomatic patient?

. Calcitonin
. Teriparatide
. Nitrogen-containing bisphosphonates
. Denosumab
. Methotrexate

Correct Answer & Explanation

. Nitrogen-containing bisphosphonates

Explanation

Nitrogen-containing bisphosphonates (such as zoledronic acid or alendronate) are the first-line treatment for symptomatic Paget's disease. They act by deeply inhibiting the overactive osteoclastic bone resorption.

Question 9112

Topic: 1. General Principles & Basic Science

A 45-year-old female with no history of renal disease presents with recurrent nephrolithiasis, diffuse bone pain, and fatigue. Laboratory tests show elevated serum calcium, decreased serum phosphorus, and elevated intact PTH. What is the most likely diagnosis?

. Primary hyperparathyroidism
. Secondary hyperparathyroidism
. Tertiary hyperparathyroidism
. Pseudohypoparathyroidism
. Familial hypocalciuric hypercalcemia

Correct Answer & Explanation

. Primary hyperparathyroidism

Explanation

Primary hyperparathyroidism typically presents with hypercalcemia, hypophosphatemia, and elevated PTH, most commonly due to a solitary parathyroid adenoma. Secondary hyperparathyroidism usually features low or normal calcium due to renal failure.

Question 9113

Topic: Biology, Genetics & Bone Healing

A 74-year-old male with Paget's disease involving the skull complains of gradually worsening hearing loss. What is the most common pathophysiologic mechanism for this specific deficit?

. Optic nerve compression
. Conductive hearing loss from ossicular ankylosis
. Sensorineural hearing loss from cochlear nerve compression
. Ototoxicity from bisphosphonate therapy
. Spontaneous vestibular schwannoma

Correct Answer & Explanation

. Sensorineural hearing loss from cochlear nerve compression

Explanation

Hearing loss is a common neurologic complication of Paget's disease involving the skull. It is most often due to sensorineural deficit caused by bony overgrowth compressing the 8th cranial nerve within the temporal bone.

Question 9114

Topic: 1. General Principles & Basic Science

A 4-year-old boy presents with severe, early-onset gout, developmental delay, and self-mutilating behaviors (lip and finger biting). A deficiency in which of the following enzymes is responsible for this condition?

. Xanthine oxidase
. Adenosine deaminase
. Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
. Glucose-6-phosphatase
. Uricase

Correct Answer & Explanation

. Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)

Explanation

Lesch-Nyhan syndrome is an X-linked recessive disorder caused by a complete deficiency of HGPRT. This leads to impaired purine salvage, resulting in severe hyperuricemia, early-onset gout, and self-mutilation.

Question 9115

Topic: 1. General Principles & Basic Science

A 52-year-old male is prescribed a medication for an acute gout attack. The drug's mechanism of action involves binding to tubulin and inhibiting microtubule polymerization. Which medication was prescribed?

. Allopurinol
. Probenecid
. Colchicine
. Febuxostat
. Pegloticase

Correct Answer & Explanation

. Colchicine

Explanation

Colchicine binds to tubulin, inhibiting microtubule polymerization. This disrupts critical cellular functions, particularly neutrophil chemotaxis and degranulation, mitigating the acute inflammatory response in gout.

Question 9116

Topic: 1. General Principles & Basic Science

A 62-year-old male is being treated for hypertension and subsequently develops his first acute gout attack. Which of the following antihypertensive medications is most likely responsible for precipitating this attack by decreasing renal urate excretion?

. Losartan
. Amlodipine
. Hydrochlorothiazide
. Lisinopril
. Metoprolol

Correct Answer & Explanation

. Losartan

Explanation

Thiazide and loop diuretics commonly precipitate gout attacks by increasing renal urate reabsorption, leading to hyperuricemia. Losartan, conversely, is unique among ARBs for having a mild uricosuric effect.

Question 9117

Topic: Biology, Genetics & Bone Healing

Which of the following laboratory profiles is most characteristic of isolated, uncomplicated Paget's disease of bone?

. Elevated serum calcium, elevated alkaline phosphatase
. Normal serum calcium, markedly elevated alkaline phosphatase
. Low serum calcium, normal alkaline phosphatase
. Normal serum calcium, normal alkaline phosphatase
. Elevated serum calcium, normal alkaline phosphatase

Correct Answer & Explanation

. Normal serum calcium, markedly elevated alkaline phosphatase

Explanation

Uncomplicated Paget's disease is characterized by a markedly elevated serum alkaline phosphatase, reflecting immense osteoblastic activity, while serum calcium and phosphorus levels typically remain within normal limits.

Question 9118

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size, hearing loss, and anterior bowing of his tibias. What is the primary cellular defect that initiates the pathogenesis of this condition?

. Osteoblast overactivity leading to disorganized lamellar bone
. Defective mineralization of newly formed osteoid
. Osteoclast abnormality with increased cellular number, size, and nucleoli
. T-cell mediated destruction of articular cartilage

Correct Answer & Explanation

. Osteoclast abnormality with increased cellular number, size, and nucleoli

Explanation

Paget's disease initiates with an intense phase of osteoclastic bone resorption followed by chaotic osteoblastic bone formation. The primary defect lies in the osteoclasts, which are abnormal, hypernucleated, and significantly increased in both size and number.

Question 9119

Topic: 1. General Principles & Basic Science

A 50-year-old male presents with severe acute pain in his first metatarsophalangeal joint. Joint aspiration is performed.

Under compensated polarized light microscopy, what are the expected characteristics of the causative crystals?

. Positively birefringent and rhomboid-shaped
. Negatively birefringent and needle-shaped
. Non-birefringent and envelope-shaped
. Positively birefringent and needle-shaped

Correct Answer & Explanation

. Negatively birefringent and needle-shaped

Explanation

Gout is caused by the deposition of monosodium urate crystals. Under compensated polarized light, these crystals exhibit strong negative birefringence (appearing yellow when parallel to the compensator axis) and are classically needle-shaped.

Question 9120

Topic: 1. General Principles & Basic Science

A 60-year-old male with recurrent gout attacks requires long-term urate-lowering therapy. He has a history of multiple radiolucent kidney stones. Which of the following medications is strictly contraindicated for this patient?

. Allopurinol
. Febuxostat
. Colchicine
. Probenecid

Correct Answer & Explanation

. Probenecid

Explanation

Probenecid is a uricosuric agent that lowers serum urate by increasing renal excretion of uric acid. It is contraindicated in patients with a history of nephrolithiasis or severe renal impairment due to the high risk of exacerbating stone formation.

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