Sample questions / Musculoskeletal & Skin

Organ system

Musculoskeletal & Skin questions for Step 1

Work through musculoskeletal & skin vignettes that mix physiology, pathology and pharmacology, the way the exam does. Every explanation covers all five options.

BiochemistryMedium

PRPP synthetase overactivity

A 45-year-old man has gout of the first MTP joint and recurrent uric acid stones. Serum urate is 12 mg/dL and 24-hour urinary uric acid is 1,200 mg/day. He has no neurologic findings and no family history.

Which enzymatic defect most likely explains the overproduction?

1. Complete HGPRT deficiency causing total purine salvage pathway failure
2. Decreased xanthine oxidase activity causing xanthine accumulation
3. Glucose-6-phosphatase deficiency causing increased purine degradation from glycogen storage
4. Increased phosphoribosyl pyrophosphate synthetase activity causing accelerated de novo purine synthesis
5. Adenine phosphoribosyltransferase deficiency causing 2,8-dihydroxyadenine accumulation

PathologyEasy

Mycosis fungoides

A 65-year-old man has scaly skin patches and plaques with lymphadenopathy. Skin biopsy shows atypical lymphocytes infiltrating the epidermis and clustering in Pautrier microabscesses. The cells are CD3+, CD4+ and CD7-.

What is the most likely diagnosis?

1. Peripheral T-cell lymphoma, NOS
2. Sézary syndrome
3. Mycosis fungoides
4. Adult T-cell leukemia/lymphoma
5. Anaplastic large cell lymphoma

ImmunologyEasy

Dermatomyositis mechanism

A 40-year-old woman has proximal weakness and a purple eyelid rash. Biopsy shows perifascicular atrophy and complement deposits on capillaries.

What mechanism explains the muscle injury?

1. Direct T-cell cytotoxicity
2. Complement-mediated microangiopathy
3. Antibody-mediated muscle fiber damage
4. Mitochondrial dysfunction
5. Necrotizing autoantibody effects

MicrobiologyMedium

Varicella risk

A pregnant woman had chickenpox at 8 weeks of pregnancy.

What is the approximate risk of congenital varicella syndrome?

1. 50%
2. 2%
3. 10%
4. <1%
5. 25%

PharmacologyEasy

Pseudocholinesterase

A healthy 32-year-old woman gets succinylcholine 1.5 mg/kg for rapid sequence intubation for appendectomy. Three hours later she is still paralyzed and ventilated, with 0/4 twitches on train-of-four. Her mother had a similar episode. Dibucaine number is 22 (normal >70).

Which enzyme is most likely deficient due to a genetic variant?

1. Monoamine oxidase B in the central nervous system
2. Hepatic N-acetyltransferase type 2
3. Butyrylcholinesterase (pseudocholinesterase)
4. Acetylcholinesterase at the neuromuscular junction
5. Catechol-O-methyltransferase

Other systems

Cardiovascular · Respiratory · Renal & Urinary · Gastrointestinal & Hepatobiliary · Nervous System · Endocrine · Reproductive · Hematology & Oncology · Behavioral Health · Multisystem & General Principles ·