Pathophysiology
P-I-14. Menopause & osteoporosis, Case 2
閉経と骨粗鱬症 症例2
A 62-year-old mother of three has been complaining of diffuse bone pain in the past few years. After her shopping this morning, as she lifted her laden basket, she felt a sudden sharp pain around the waist. The X-ray taken in the ER showed compression fracture of vertebra L1. She is not on any medication; however, she takes soy-based plant supplements (phytooestrogen) and vitamin E.
Her annual gynaecological screenings usually find everything in order. Her last mammography was negative. She had her last menstrual period at the age of 47. She does not smoke or drink alcohol, and is physically inactive.
Her mother had had osteoporosis and type-2 diabetes mellitus. Her father had been treated for hypertension.
Physical examination:
- height: 165 cm
- weight: 58 kg
- blood pressure: 125/80 Hgmm
Blood:
- Na⁺: 138 mmol/L
- K⁺: 4.1 mmol/L
- Cl⁻: 103 mmol/L
- Ca²⁺: 2.2 mmol/L
- PO₄³⁻: 1.1 mmol/L
- albumin: 33 g/L
- 25(OH) vitamin D level: 22 ng/mL (20-40 ng/mL)
- BUN: 6 mmol/L
- creatinine: 84 µmol/L
- glucose: 4.3 mmol/L
- oestradiol: 4 pg/mL (low)
- TSH: 2.1 mU/L (0.300-4.200 mU/L)
- ASAT: 21 U/L
- ALAT: 25 U/L
- ALP: 98 U/L
- total bilirubin: 17 µmol/L
- direct bilirubin: 2.8 µmol/L
- total cholesterol: 4.9 mmol/L
- HDL: 1.1 mmol/L
- LDL: 2.35 mmol/L
- triglyceride: 1.6 mmol/L
- ESR: 9 mm/h
Urine:
- pH: 7.8
- protein: negative
- glucose: negative
- bilirubin: negative
- ketone bodies: negative
- specific gravity: 1015 g/L
Urine sediment: no white blood cells, red blood cells or bacteria detected
DEXA scan: lumbar spine T-score: -2.9 SD
Key Quotes & What They Tell Us
| Quote / Value | Interpretation |
|---|---|
| “lifted her laden basket, she felt a sudden sharp pain”; X-ray “compression fracture of vertebra L1” | Low-energy fragility fracture — hallmark of established osteoporosis |
| “last menstrual period at the age of 47”; oestradiol 4 pg/mL (low) | Postmenopausal oestrogen deficiency → the main driver of accelerated bone loss |
| “physically inactive”; mother had osteoporosis | Inactivity and family history add to fracture risk |
| Ca²⁺ 2.2, PO₄³⁻ 1.1 mmol/L (normal); creatinine 84 (normal) | Normal calcium/phosphate and renal function — excludes hyperparathyroidism and renal bone disease |
| 25(OH) vitamin D 22 ng/mL (low-normal) | Borderline vitamin D may contribute but is not the primary cause |
| DEXA lumbar T -2.9 SD | Osteoporosis (T ≤ -2.5) confirmed by bone densitometry |
Key Points
- Diagnosis: Postmenopausal (type I) osteoporosis with an osteoporotic vertebral compression fracture (L1).
- Pathophysiology: Oestrogen loss after menopause → increased osteoclast activity → net bone resorption > formation → reduced bone density and fragility.
- Distinguishing labs: Normal calcium, phosphate, and renal function separate this from primary/secondary hyperparathyroidism.
- Risk factors: Menopause, physical inactivity, low-normal vitamin D, and family history.
- Implication: A fragility fracture itself defines severe osteoporosis and warrants treatment regardless of T-score.
一問一答
▶In the Case 2 patient (L1 compression fracture, low estradiol, normal calcium), what is the diagnosis?
Postmenopausal (type I) osteoporosis with an osteoporotic vertebral compression fracture.
▶What is the pathophysiology of postmenopausal osteoporosis?
Estrogen loss increases osteoclast activity so bone resorption exceeds formation, reducing bone density and causing fragility.
▶What is a fragility fracture, and why is it significant in Case 2?
A low-energy fracture (e.g., from lifting a basket) — a hallmark of established osteoporosis that itself defines severe disease warranting treatment.
▶How do normal calcium, phosphate, and creatinine help in Case 2?
They exclude hyperparathyroidism and renal bone disease, supporting primary postmenopausal osteoporosis.
▶What does a low estradiol (4 pg/mL) indicate in Case 2?
Postmenopausal estrogen deficiency — the main driver of accelerated bone loss.
▶What modifiable and non-modifiable risk factors raised this patient's fracture risk?
Physical inactivity and low-normal vitamin D (modifiable); menopause and family history of osteoporosis (non-modifiable).
▶Why is the L1 vertebra a typical site for osteoporotic compression fractures?
The thoracolumbar junction bears high mechanical load on trabecular-rich vertebral bone, which is preferentially lost in osteoporosis.
▶Why is estrogen protective for bone?
Estrogen restrains osteoclast activity and promotes osteoclast apoptosis, limiting bone resorption.
▶What DEXA result confirmed osteoporosis in Case 2?
Lumbar spine T-score of -2.9 SD (≤ -2.5).
▶How does postmenopausal (type I) osteoporosis differ from senile (type II) osteoporosis?
Type I is estrogen-deficiency-driven with predominant trabecular bone loss (vertebral fractures); type II is age-related affecting both cortical and trabecular bone (hip fractures).
▶Why is the patient's borderline vitamin D (22 ng/mL) relevant?
Low-normal vitamin D may contribute to bone loss but is not the primary cause in this case.
▶Why does physical inactivity worsen osteoporosis?
Weight-bearing/mechanical loading stimulates bone formation; inactivity reduces this stimulus, accelerating bone loss.
▶Why is serum calcium typically normal in postmenopausal osteoporosis?
Bone loss is from imbalanced remodeling, not a calcium-regulating hormone disorder, so serum calcium stays normal.
▶What first-line drug class is used to treat postmenopausal osteoporosis?
Bisphosphonates (antiresorptive agents).
▶What lifestyle measures help prevent/treat osteoporosis?
Weight-bearing exercise, adequate calcium and vitamin D, smoking/alcohol avoidance, and fall prevention.
▶Why does a fragility fracture warrant treatment regardless of T-score?
A low-energy fracture itself defines severe (established) osteoporosis, indicating high fracture risk.
▶What is the role of phytoestrogen supplements in osteoporosis?
They are weak estrogen-like compounds with limited proven benefit and do not substitute for proven osteoporosis therapy.
▶What does diffuse bone pain over years suggest in an aging postmenopausal woman?
Progressive osteoporosis with microarchitectural deterioration, predisposing to fracture.
▶Why is a normal TSH reassuring in an osteoporosis workup?
Hyperthyroidism accelerates bone loss; a normal TSH excludes it as a secondary cause.
▶How does the timing of menopause (age 47) relate to osteoporosis risk?
Years of estrogen deficiency since menopause cumulatively accelerate bone loss, increasing fracture risk.