Soru

A primary care physician evaluates a female patient who reports 14 months of progressively worsening deep pain in her ribs and lower extremities. The patient, a 42-year-old architect, also describes profound proximal muscle weakness, noting that she now requires the use of her arms to stand up from a seated position. She has no significant past medical history and takes no medications. Vital signs are within normal limits. Physical examination reveals tenderness to palpation over the anterior ribs bilaterally and 4/5 strength in the proximal hip flexors.

Laboratory studies reveal the following:

Further evaluation shows a fractional excretion of phosphorus of 28% (normal in the setting of hypophosphatemia: <5%). Radiographs of the pelvis demonstrate symmetric, thin, radiolucent lines perpendicular to the cortex of the femoral necks.

Which of the following best describes the underlying paraneoplastic mechanism responsible for this patient's condition, and the most appropriate next step in management to confirm the etiology?