1. General Principles & Basic Science MCQs

A bone biopsy is obtained from the pelvis of an asymptomatic 65-year-old man who was noted to have an incidental sclerotic lesion on a radiograph. Histological examination reveals a disordered, 'mosaic' pattern of lamellar bone with prominent, irregular cement lines. The primary initial defect in this patient's disease process involves which of the following cell types?

A 52-year-old man with a history of recurrent gouty attacks is started on allopurinol for long-term management. Through which of the following mechanisms does this medication exert its therapeutic effect?

A 70-year-old woman with Paget's disease presents with increasing right thigh pain and bowing of the femur. She is prescribed an intravenous nitrogen-containing bisphosphonate (zoledronic acid). This class of medication functions primarily by inhibiting which of the following enzymes?

A 72-year-old man presents with progressive bowing of his right tibia and a deep, aching bone pain. Radiographs show cortical thickening and trabecular coarsening. A bone biopsy reveals woven bone with a mosaic pattern of prominent cement lines. Which of the following describes the primary cellular abnormality responsible for this condition?

A 60-year-old woman is diagnosed with primary hyperparathyroidism due to a parathyroid adenoma. Dual-energy X-ray absorptiometry (DEXA) demonstrates generalized osteopenia. Parathyroid hormone (PTH) stimulates bone resorption primarily by binding directly to receptors on which of the following cell types?

A 55-year-old man with recurrent gouty arthropathy is started on daily allopurinol for long-term medical management. Which of the following describes the primary mechanism of action of this medication?

A 42-year-old man presents with an acutely swollen and erythematous right knee. Joint aspiration yields synovial fluid with a white blood cell count of 35,000/uL. Under polarized light microscopy with a red compensator, the crystals appear yellow when aligned parallel to the axis of the compensator. Which of the following is the most likely diagnosis?

A 58-year-old man with end-stage renal disease (ESRD) presents with diffuse bone pain. He is diagnosed with renal osteodystrophy and secondary hyperparathyroidism. Which of the following laboratory profiles is most consistent with this patient's condition?

A 70-year-old woman is diagnosed with active Paget's disease due to severe long bone pain and markedly elevated alkaline phosphatase. She is prescribed intravenous zoledronic acid. What is the primary intracellular target of this class of medication?

A 6-year-old boy presents with a prominent forehead, ability to appose his shoulders anteriorly, and the skull radiograph shown.

What gene is mutated in this condition?

A 65-year-old man presents with increasing hat size, unilateral hearing loss, and a painful, bowed tibia. Labs show an isolated, highly elevated alkaline phosphatase. Which of the following cells is the primary driver of this disease process?

A 5-year-old boy presents with progressive genu varum. Laboratory studies show normal calcium, low phosphorus, normal parathyroid hormone, and normal vitamin D levels. A mutation in the PHEX gene is confirmed. What is the primary mechanism of hypophosphatemia in this patient?

A 6-year-old boy presents with delayed closure of the cranial fontanelles, dental abnormalities, and the ability to appose his shoulders anteriorly.

Radiographs confirm the diagnosis. Which gene is most likely mutated in this patient?

A 4-year-old with multiple fractures and blue sclerae is started on cyclical pamidronate therapy.

By what mechanism does this medication improve bone mineral density?

A newborn presents with severe anemia, cranial nerve palsies, and a diffusely dense, "bone-within-bone" appearance on radiographs. A defect in which of the following mechanisms is the primary cause?

A 7-year-old boy presents with a waddling gait, short stature, and hip pain. Radiographs show delayed ossification of the capital femoral epiphyses and platyspondyly with normal interpedicular distances. Which protein is most likely defective?

A newborn presents with short-limbed dwarfism, "hitchhiker" thumbs, rigid clubfeet, and "cauliflower" ears. A mutation in which gene is responsible for this condition?

A 65-year-old man presents with a progressively increasing hat size, hearing loss, and a painful bowing deformity of his tibia. A bone biopsy in the initial lytic phase would most likely show which primary abnormality?

A 7-year-old boy presents for evaluation of an abnormal gait. Radiographs show delayed ossification of the pubic symphysis, coxa vara, and absent clavicles.

This condition is caused by a mutation in which of the following transcription factors?