A 62-year-old postmenopausal woman presents with a T-score of −2.8 on DEXA scan. Which is the most common cause of osteoporosis in this patient?

Explanation

## Epidemiology of Osteoporosis Causes **Key Point:** Postmenopausal osteoporosis (Type I) is the most common form of osteoporosis globally, accounting for approximately 80% of all cases in women. Estrogen deficiency is the primary driver. ## Mechanism of Estrogen-Deficiency Osteoporosis Estrogen loss at menopause leads to: 1. Increased osteoclast activity and lifespan 2. Decreased osteoblast function 3. Net bone resorption exceeding formation 4. Rapid trabecular bone loss (especially in spine and femoral neck) ## Comparison of Common Causes | Cause | Prevalence | Age of Onset | Bone Loss Pattern | Gender Predominance | |-------|-----------|--------------|-------------------|---------------------| | Estrogen deficiency (Type I) | ~80% of female cases | 50–70 years | Trabecular > cortical | Female | | Corticosteroid-induced | ~5–10% of all cases | Any age on chronic steroids | Trabecular and cortical | Both | | Hyperparathyroidism | ~3–5% of cases | 50+ years | Cortical > trabecular | Female | | Malabsorption | <2% of cases | Variable | Generalized | Both | **High-Yield:** In a postmenopausal woman with osteoporosis, estrogen deficiency is the diagnosis until proven otherwise. The T-score of −2.8 confirms osteoporosis (T-score ≤ −2.5). **Clinical Pearl:** Postmenopausal women lose bone at a rate of 2–3% per year for the first 5–10 years after menopause, then 0.5–1% per year thereafter. This accelerated phase is pathognomonic for estrogen deficiency. ## Why Estrogen Deficiency Is Most Common - Affects ~1 in 3 women over age 50 - Corticosteroid-induced osteoporosis is the second most common secondary cause, but still far less frequent than postmenopausal osteoporosis - Hyperparathyroidism and malabsorption are rare causes in comparison