Musculoskeletal and Skin Disorders Practice Questions
20 free Musculoskeletal and Skin Disorders practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
A 72-year-old woman presents with a hip fracture after a minor fall. DEXA scan shows a T-score of –2.8. Which pathophysiologic process is most characteristic of osteoporosis?
- A Globally decreased osteoclast activity
- B Markedly increased osteoblast activity
- C Normal mineralization, low bone mass
- D Defective osteoid matrix formation
Correct answer: Normal mineralization, low bone mass
Osteoporosis is characterized by normal mineralization but reduced total bone mass. Bone microarchitecture deteriorates, predisposing to fractures.
A patient with psoriasis develops silvery scales on extensor surfaces. Which histologic feature is classically seen?
- A Hypergranulosis
- B Munro microabscesses
- C Subepidermal blisters
- D Widened dermal papillae
Correct answer: Munro microabscesses
Munro microabscesses (neutrophils in the stratum corneum) are characteristic of psoriasis. The condition also shows parakeratosis and acanthosis.
Which factor increases a patient’s risk of developing osteoporosis?
- A Long-standing obesity
- B Late natural menopause
- C Chronic glucocorticoid use
- D Persistently high estrogen levels
Correct answer: Chronic glucocorticoid use
Glucocorticoids decrease bone formation and increase bone resorption. Long-term use is a major secondary cause of osteoporosis.
A patient with psoriasis experiences worsening symptoms after streptococcal pharyngitis. Which type of hypersensitivity is implicated?
- A Type I hypersensitivity
- B Type II hypersensitivity
- C Type III hypersensitivity
- D Type IV hypersensitivity
Correct answer: Type IV hypersensitivity
Psoriasis is a Type IV (T-cell–mediated) hypersensitivity reaction, with T cells driving keratinocyte proliferation. Infections such as streptococcal pharyngitis can trigger or exacerbate disease activity.
Which medication reduces the risk of vertebral and hip fractures in osteoporosis by inhibiting osteoclast activity?
- A Teriparatide
- B Alendronate
- C Raloxifene
- D Calcitonin
Correct answer: Alendronate
Alendronate is a bisphosphonate that inhibits osteoclasts, reducing bone resorption. It reduces both vertebral and hip fracture risk.
A patient with psoriasis asks about nail findings associated with the disease. Which finding is characteristic?
- A Beau lines
- B Pitting
- C Onycholysis from Candida
- D Subungual hematoma
Correct answer: Pitting
Nail pitting results from psoriatic involvement of the nail matrix. It is a common associated finding.
A postmenopausal woman begins estrogen replacement therapy. How does estrogen affect bone physiology?
- A Stimulates osteoclast differentiation
- B Decreases osteoprotegerin (OPG) levels
- C Inhibits RANKL activity
- D Inhibits osteoblasts
Correct answer: Inhibits RANKL activity
Estrogen inhibits RANKL-mediated osteoclast activation by increasing OPG. Loss of estrogen increases bone resorption.
Which cytokine plays a major role in the pathogenesis of psoriasis?
- A IL-2
- B IL-23
- C IL-10
- D TNF-β
Correct answer: IL-23
IL-23 promotes differentiation and maintenance of Th17 cells, which drive psoriatic inflammation. This pathway is a major therapeutic target.
A patient presents with vertebral compression fractures. Which lab abnormality is expected in primary osteoporosis?
- A Elevated parathyroid hormone
- B Elevated alkaline phosphatase
- C Elevated serum calcium
- D Normal calcium, phosphate, and PTH
Correct answer: Normal calcium, phosphate, and PTH
Primary osteoporosis does not alter calcium, phosphate, or PTH levels. Diagnosis relies on bone density and fracture risk.
A patient with psoriasis is started on a TNF-α inhibitor. What is the major risk of this therapy?
- A Severe hypoglycemia
- B Latent tuberculosis reactivation
- C New-onset hyperthyroidism
- D Acute anaphylactic reactions
Correct answer: Latent tuberculosis reactivation
TNF-α inhibitors suppress immune function, increasing risk of latent TB reactivation. Screening for TB is required before treatment.
A 65-year-old woman with osteoporosis begins teriparatide therapy. What is its mechanism?
- A Continuous PTH exposure to increase bone resorption
- B Intermittent PTH exposure to increase bone formation
- C Inhibition of osteoblast differentiation
- D Increase in RANKL production
Correct answer: Intermittent PTH exposure to increase bone formation
Intermittent PTH analog use stimulates osteoblasts more than osteoclasts, promoting bone formation. Continuous exposure has opposite effects.
A pediatric patient with guttate psoriasis presents after a recent streptococcal infection. What is the typical distribution of lesions?
- A Flexor surfaces and folds
- B Extensor surfaces and trunk
- C Face and scalp exclusively
- D Palms and soles only
Correct answer: Extensor surfaces and trunk
Guttate psoriasis produces small, drop-like lesions on the trunk and extensor surfaces. It commonly follows strep pharyngitis.
A patient presents with low-trauma fractures. Which lifestyle factor contributes most strongly to osteoporosis?
- A Excessive sunlight exposure
- B High-protein diet
- C Sedentary lifestyle
- D High caffeine intake
Correct answer: Sedentary lifestyle
Physical inactivity reduces mechanical bone loading, accelerating bone loss. Weight-bearing exercise helps prevent osteoporosis.
Which finding is characteristic of psoriatic arthritis rather than osteoarthritis?
- A Stiffness improving with activity
- B Symmetric joint space narrowing
- C Marginal osteophyte formation
- D Heberden node formation
Correct answer: Stiffness improving with activity
Psoriatic arthritis produces inflammatory joint symptoms that improve with activity. Osteoarthritis worsens with use.
A patient with osteoporosis begins denosumab therapy. Which pathway is targeted?
- A RANKL inhibition
- B Estrogen receptor activation
- C Inhibition of osteoblasts
- D Activation of calcitonin receptors
Correct answer: RANKL inhibition
Denosumab is a monoclonal antibody against RANKL, preventing osteoclast activation. It reduces bone resorption.
Which of the following nail findings is MOST specific for psoriasis?
- A Transverse horizontal ridging
- B Distal nail onycholysis
- C Oil-drop discoloration
- D Spoon-shaped koilonychia
Correct answer: Oil-drop discoloration
Oil-drop (salmon patch) discoloration is highly characteristic of psoriatic nail involvement. It reflects nail bed inflammation.
A 60-year-old woman develops vertebral fractures despite adequate calcium intake. Her labs show low vitamin D levels. What is the mechanism?
- A Reduced intestinal calcium uptake
- B Increased urinary calcium loss
- C Increased osteoblast activity
- D Increased bone mineralization
Correct answer: Reduced intestinal calcium uptake
Vitamin D deficiency reduces calcium absorption, leading to secondary hyperparathyroidism and bone loss. This accelerates osteoporosis.
A biopsy of a psoriatic plaque shows parakeratosis. What does this indicate?
- A Nuclei retained in stratum corneum
- B Edema of the dermis
- C Loss of the granular cell layer
- D Vacuolization of basal keratinocytes
Correct answer: Nuclei retained in stratum corneum
Parakeratosis refers to retention of nuclei in the stratum corneum and reflects accelerated keratinocyte turnover. It is a hallmark of psoriasis.
Which comorbidity is strongly associated with psoriasis due to chronic systemic inflammation?
- A Hypothyroidism
- B Metabolic syndrome
- C Adrenal insufficiency
- D Asthma
Correct answer: Metabolic syndrome
Psoriasis is linked to metabolic syndrome, insulin resistance, and increased cardiovascular risk due to systemic inflammation.
A patient with osteoporosis sustains a Colles fracture. This involves which bone?
- A Proximal humerus
- B Distal radius
- C Ulna shaft
- D Scaphoid
Correct answer: Distal radius
Colles fractures involve the distal radius after a fall on an outstretched hand. They are common in patients with osteoporosis.