UWorld UWorld System-Based Pathology 2

Question 1

In UWorld musculoskeletal pathology, which crystal arthropathy shows needle-shaped negatively birefringent crystals under polarized light?

Accepted Answer

Gout (monosodium urate crystals)

Answer

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?

Accepted Answer

Confusion, ophthalmoplegia, and ataxia caused by thiamine (B1) deficiency, commonly in alcoholics

Answer

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?

Accepted Answer

Psoriasis

Answer

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?

Accepted Answer

It inhibits dihydrofolate reductase, blocking DNA synthesis and causing trophoblastic cell death

Answer

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?

Accepted Answer

MRSA produces an altered penicillin-binding protein (PBP2a) encoded by the mecA gene that has low affinity for beta-lactams

Answer

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.

UWorld Practice Test

UWorld Practice Test

UWorld UWorld System-Based Pathology 2