UWorld UWorld System-Based Pathology 2 — Questions and Answers
Question 1: In UWorld musculoskeletal pathology, which crystal arthropathy shows needle-shaped negatively birefringent crystals under polarized light?
- Gout (monosodium urate crystals) (Correct answer)
- Pseudogout (calcium pyrophosphate crystals)
- Septic arthritis
- Reactive arthritis
Correct answer: Gout (monosodium urate crystals)
Monosodium urate crystals in gout are needle-shaped and negatively birefringent (yellow when parallel to the compensator), while CPPD crystals in pseudogout are rhomboid and positively birefringent.
Question 2: In UWorld neurology, what is the classic presentation of Wernicke encephalopathy and its underlying cause?
- Confusion, ophthalmoplegia, and ataxia caused by thiamine (B1) deficiency, commonly in alcoholics (Correct answer)
- Memory loss and confabulation from B12 deficiency
- Tremors and rigidity from dopamine depletion
- Bilateral arm weakness from cervical cord compression
Correct answer: Confusion, ophthalmoplegia, and ataxia caused by thiamine (B1) deficiency, commonly in alcoholics
Wernicke encephalopathy presents with the classic triad of confusion, eye movement abnormalities, and gait ataxia due to thiamine deficiency, requiring immediate IV thiamine treatment.
Question 3: Which UWorld dermatology condition is characterized by hyperkeratotic, silvery plaques on extensor surfaces with nail pitting and is associated with HLA-Cw6?
- Psoriasis (Correct answer)
- Lichen planus
- Seborrheic dermatitis
- Pityriasis rosea
Correct answer: Psoriasis
Psoriasis presents with well-demarcated, silvery-scaled plaques on extensor surfaces, nail pitting, and is associated with HLA-Cw6 and systemic conditions like psoriatic arthritis.
Question 4: In UWorld reproductive pathology, what is the mechanism of action of methotrexate when used to treat ectopic pregnancy?
- It inhibits dihydrofolate reductase, blocking DNA synthesis and causing trophoblastic cell death (Correct answer)
- It induces prostaglandin-mediated cervical ripening to expel the ectopic tissue
- It blocks progesterone receptors, terminating trophoblast support
- It promotes endometrial shedding to displace the ectopic implant
Correct answer: It inhibits dihydrofolate reductase, blocking DNA synthesis and causing trophoblastic cell death
Methotrexate is a folate antagonist that inhibits DHFR, halting DNA synthesis in rapidly dividing trophoblastic cells and allowing the ectopic pregnancy to resolve without surgery.
Question 5: In UWorld infectious disease, what is the mechanism of resistance in MRSA that makes beta-lactam antibiotics ineffective?
- MRSA produces an altered penicillin-binding protein (PBP2a) encoded by the mecA gene that has low affinity for beta-lactams (Correct answer)
- MRSA produces a beta-lactamase enzyme that hydrolyzes all beta-lactam rings
- MRSA efflux pumps expel beta-lactam antibiotics before they can act
- MRSA lacks a cell wall, making beta-lactams irrelevant
Correct answer: MRSA produces an altered penicillin-binding protein (PBP2a) encoded by the mecA gene that has low affinity for beta-lactams
The mecA gene in MRSA encodes PBP2a, an alternative penicillin-binding protein with very low affinity for all beta-lactam antibiotics, rendering the entire class ineffective.
Question 6: In UWorld psychiatry, what distinguishes major depressive disorder (MDD) from persistent depressive disorder (dysthymia)?
- MDD requires discrete episodes with at least 5 DSM criteria for 2+ weeks, while dysthymia involves chronically depressed mood for at least 2 years with fewer symptoms (Correct answer)
- MDD lasts at least 6 months while dysthymia lasts only 2 weeks
- Dysthymia includes psychotic features while MDD does not
- MDD is treated with therapy only while dysthymia requires medication exclusively
Correct answer: MDD requires discrete episodes with at least 5 DSM criteria for 2+ weeks, while dysthymia involves chronically depressed mood for at least 2 years with fewer symptoms
MDD requires a distinct episode of 5 or more depressive symptoms for at least 2 weeks, while dysthymia (PDD) is characterized by chronic low-grade depressed mood lasting at least 2 years with fewer diagnostic criteria.
UWorld UWorld System-Based Pathology 2
In UWorld musculoskeletal pathology, which crystal arthropathy shows needle-shaped negatively birefringent crystals under polarized light?