A 62-year-old postmenopausal woman undergoes DEXA scan for osteoporosis screening. Her T-score is −2.8 at the lumbar spine. Regarding the pathophysiology and management of osteoporosis, all of the following are true EXCEPT:

Explanation

## Mechanism of Action in Osteoporosis Treatment **Key Point:** Teriparatide is an anabolic agent, NOT an antiresorptive. This is a critical distinction that is frequently tested. ### Antiresorptive vs. Anabolic Agents | Agent Class | Mechanism | Example | |---|---|---| | **Antiresorptive** | Inhibit osteoclast activity or recruitment | Bisphosphonates, Denosumab, HRT, Calcitonin | | **Anabolic** | Stimulate osteoblast activity and new bone formation | Teriparatide (PTH 1-34), Abaloparatide | ### Correct Statements Explained **Option 1 (Bisphosphonates):** Bisphosphonates contain a P-C-P backbone that binds to bone mineral and is internalized by osteoclasts. They inhibit farnesyl pyrophosphate synthase in the mevalonate pathway, preventing osteoclast cytoskeletal rearrangement and leading to apoptosis. ✓ TRUE **Option 2 (Estrogen deficiency):** Estrogen normally suppresses RANKL expression on osteoblasts and increases osteoprotegerin (OPG). Postmenopausal estrogen deficiency → ↑ RANKL → ↑ osteoclast differentiation and bone resorption. ✓ TRUE **Option 3 (Denosumab):** Denosumab is a monoclonal antibody against RANKL. It blocks the RANK-RANKL interaction, preventing osteoclast precursor recruitment and differentiation, thereby reducing bone resorption and increasing BMD. ✓ TRUE **Option 4 (Teriparatide):** ✗ FALSE — Teriparatide is a recombinant PTH 1-34 that acts as an **anabolic agent**. It stimulates osteoblasts to increase bone formation when given in intermittent pulses. It does NOT primarily suppress osteoclast activity. **High-Yield:** Teriparatide is reserved for severe osteoporosis or when antiresorptive therapy has failed because it requires daily subcutaneous injection and carries a black-box warning for osteosarcoma (from animal studies). It is the only approved anabolic agent for osteoporosis in most countries. **Clinical Pearl:** The anabolic effect of teriparatide is paradoxical — PTH in continuous high doses causes bone loss (via osteoclast activation), but intermittent low-dose PTH causes bone gain (via osteoblast stimulation). This is why dosing schedule is critical. **Mnemonic:** **AABCO** — Antiresorptive Agents Block Osteoclasts; Anabolic Agents Build Osteoblasts.