A 52-year-old woman with rheumatoid arthritis has been on long-term corticosteroid therapy for 8 years. She now presents with severe osteoporosis and pathological fractures. Which is the most common adverse effect of prolonged corticosteroid use that has led to her bone loss?

## Corticosteroid-Induced Osteoporosis: Mechanism **Key Point:** Corticosteroids cause osteoporosis primarily through **inhibition of osteoblast function** and **increased osteoclast-mediated bone resorption**. ### Mechanism of Bone Loss 1. **Osteoblast suppression**: Corticosteroids directly reduce osteoblast proliferation and differentiation, decreasing bone formation 2. **Increased osteoclast activity**: Enhanced RANKL signalling and reduced osteoprotegerin (OPG) production lead to increased bone resorption 3. **Reduced calcium absorption**: Decreased intestinal calcium absorption due to impaired vitamin D action 4. **Increased urinary calcium loss**: Enhanced renal calcium wasting ### Timeline of Corticosteroid-Induced Bone Loss **High-Yield:** Bone loss is **most rapid in the first 3–6 months** of corticosteroid therapy, with loss of 5–10% of bone mass annually in untreated patients. This patient's 8-year exposure represents cumulative significant skeletal damage. ### Risk Factors for Severe Osteoporosis | Factor | Impact | |--------|--------| | Dose ≥7.5 mg/day prednisolone equivalent | High risk | | Duration >3 months | Cumulative effect | | Age >50 years | Baseline bone loss | | Female sex | Lower peak bone mass | | Postmenopausal status | Oestrogen deficiency | **Clinical Pearl:** Corticosteroid-induced osteoporosis is the **most common secondary cause of osteoporosis** in clinical practice, more frequent than hyperparathyroidism or hyperthyroidism. ### Prevention and Management **Mnemonic: CALCIUM-D** - **C**alcium supplementation (1000–1200 mg/day) - **A**ctive lifestyle and weight-bearing exercise - **L**imit corticosteroid dose to minimum effective - **C**onsider bisphosphonates (alendronate, risedronate) - **I**nspect baseline DEXA scan - **U**se vitamin D (cholecalciferol 800–2000 IU/day) - **M**onitor bone density annually - **D**rug interactions (avoid concurrent medications that impair absorption) **Tip:** All patients on corticosteroids ≥7.5 mg/day for ≥3 months should receive bone-protective therapy with calcium, vitamin D, and consideration of bisphosphonates.