Osteoporosis
Summary
Osteoporosis is a reduction in bone mass with normal bone mineralization, leading to fragility fractures (vertebral compression, hip, distal radius). Defined by DEXA T-score <= -2.5; most common in postmenopausal women due to estrogen deficiency.
Detail
Bone remodeling is balanced by osteoblasts (formation) and osteoclasts (resorption); in osteoporosis, resorption outpaces formation. Estrogen normally inhibits RANKL-mediated osteoclast activation, so postmenopausal estrogen loss increases osteoclast activity (Type I, postmenopausal osteoporosis). Type II (senile) affects both sexes >70 due to age-related decline in osteoblast function. Secondary causes: chronic glucocorticoids (most common drug cause), hyperparathyroidism, hyperthyroidism, hypogonadism, multiple myeloma, malabsorption, anorexia, smoking, and alcohol. Labs are typically normal (Ca, Phos, PTH, ALP) -- this distinguishes it from osteomalacia and hyperparathyroidism. Treatment: bisphosphonates (first line, inhibit osteoclasts), denosumab (anti-RANKL), teriparatide (PTH 1-34, anabolic), calcium/vitamin D, weight-bearing exercise. Boards classic: postmenopausal woman with vertebral compression fracture, T-score -3.0, normal labs.
Sources
- First Aid for USMLE Step 1 2024
- Robbins Basic Pathology 10th ed
- Pathoma
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