On this page
Study tools
Write your answer
Saved on this device. No marking — you are the marker.
Stem
A 70-year-old man is found on routine bloods to have an alkaline phosphatase of 520 U/L (reference 40-120), with a normal gamma-GT, calcium 2.32 mmol/L, and phosphate 1.05 mmol/L. Liver ultrasound is normal. He has noticed his hat size increasing over the last year and his wife remarks his skull looks "bigger," with some hearing decline in the right ear. He has an aching pain in the right thigh. Examination reveals warmth over the right tibia, which is slightly bowed, and a normal neurological examination.
Questions
a) What is the most likely diagnosis, and which single biochemical feature from the stem most supports it? (2 marks)
Model answer: Paget disease of bone (osteitis deformans) (1 mark). The single most supportive feature is a markedly raised alkaline phosphatase with NORMAL calcium and NORMAL phosphate (and a normal gamma-GT, confirming a bone source) — the biochemical signature of Paget disease (1 mark).
b) Outline the investigations you would perform to confirm the diagnosis and define the extent of disease. (3 marks)
Model answer: Plain X-rays of affected bones — cortical thickening, mixed lytic-sclerotic lesions, bone expansion and bowing, cotton-wool skull, picture-frame vertebrae, blade-of-grass lytic edge (1). A technetium-99m isotope bone scan — the most sensitive test for extent, showing focal hot spots and defining the number of sites (1). Bone turnover markers (bone-specific ALP, P1NP), 25-hydroxyvitamin D before treatment, and audiometry for the hearing loss; MRI/biopsy only if osteosarcoma is suspected (1).
c) Describe the first-line treatment, naming the drug, route and an essential co-prescription. (3 marks)
Model answer: First-line is a single 5 mg intravenous zoledronate infusion — the most potent bisphosphonate, normalising ALP for months to years in most patients (1). Ensure adequate calcium and vitamin D before and after the infusion to avoid treatment-induced hypocalcaemia (1). Analgesia and a hearing aid for symptoms; monitor alkaline phosphatase to track response, re-treating on biochemical or symptomatic relapse (1).
d) Name three complications of Paget disease and state the single clinical feature that should raise concern for osteosarcoma. (2 marks)
Model answer: Any three of: pathological fracture, deafness, high-output cardiac failure, spinal cord / nerve-root compression, basilar invagination (platybasia), secondary osteoarthritis, or hypercalcaemia of immobilisation (1). The feature raising concern for osteosarcoma transformation is new, severe, or rapidly worsening pain (especially with a soft-tissue mass) in a known Pagetoid lesion — requiring urgent imaging and biopsy (1).