№ 10Rheumatology17 min read
Disorders of bone metabolism and bone turnover: osteoporosis, Paget’s disease, osteomalacia, osteonecrosis
1. Big picture
These four diseases are commonly confused because all can cause bone pain, fractures, deformity, or abnormal imaging, but the mechanisms are different:
| Disease | Core problem | Key exam clue |
|---|---|---|
| Osteoporosis | Low bone mass + fragile microarchitecture | Fragility fracture, low DEXA T-score, normal Ca/P/ALP |
| Osteomalacia | Poor mineralization of osteoid | Bone pain, proximal weakness, low vitamin D, ↑ alkaline phosphatase |
| Paget’s disease of bone | Excessive disorganized bone remodeling | Older patient, bone enlargement/deformity, isolated ↑ alkaline phosphatase |
| Osteonecrosis | Bone death from impaired blood supply | Steroid/alcohol/trauma + hip pain; MRI is best early test |
The examiner wants you to distinguish:
Osteoporosis = “too little bone.” Osteomalacia = “soft poorly mineralized bone.” Paget = “too much chaotic bone turnover.” Osteonecrosis = “dead bone from ischemia.”
PART I — OSTEOPOROSIS
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