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NBME 23 Answers

nbme23/Block 3/Question#43

A 65-year-old man has had increasing shortness of ...

Osteitis deformans (Paget disease)

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submitted by sajaqua1(278),

In an elderly patient with isolated elevated alkaline phosphatase (normal serum calcium and phosphate) Paget's disease of bone should be at the top of the differential. This disease is due to dysregulation of osteoclastic and osteoblastic activity; first an initial osteoclast hyperactivity phase, then increased osteoblast activity for a mixture, then osteoclasts "burnout" leading to over-mineralization and sclerotic bone plaques. In addition, this can create arteriovenous shunts in the bones which decreases resistance, leading to high output cardiac failure (a similar problem can arise in arteriovenous fistulas from blood dialysis). On histology it will have a "mosaic" pattern.

A)- Aneurysmal bone cyst- largely a product of hyperactivity of osteoclasts, this occurs more often in the limbs, and shows a cystic space with balloon-like dilation. B) Angiosarcoma- angiosarcoma of the bone is n almost purely lytic lesion. They occur more frequently in younger people. C) Niacin deficiency- I can find nothing about vitaminb B3 deficiency involving bones. B3 deficienct results in pellagra, with the classic Three D's- dermatitis (rash necklace on C3/C4 dermatome), dementia, and diarrhea. E) Osteosarcoma- Found almost exclusively in younger people, this bone growth occurs at the growth plate, particularly at the proximal end of the tibia, distal end of the femur, or proximal end of the humerus (in the long bones around your knees or at your shoulders). It shows a large, solid growing mass that may raise the periosteum in a sunburst pattern/Codman's triangle. F) Prostatic carcinoma- rare for being one of, if not the only metastatic bone cancer that is purely osteoblastic.

alexb  Great explanation, except that there was a question in NBME 22 in which the prostatic carcinoma was osteolytic. One of the commenters here looked it up and apparently it's like that 30% of the time or something. So I guess you would have to use the high output HF, normal Ca, high ALP, and mosaic pattern to "play odds" as Goljan would say. +