Pathophysiology
P-I-15. Menopause & osteoporosis, Case 3
閉経と骨粗鱬症 症例3
A 60-year-old female patient with type 2 diabetes mellitus has been receiving hemodialysis for 15 years. She consulted her GP complaining of chest pain (angina). There is no record of heart disease in her anamnesis. Her mother and two siblings were also diagnosed with diabetes mellitus earlier; her father died of a heart attack.
Physical examination:
- height: 160 cm
- weight: 70 kg
- blood pressure: 122/83 Hgmm
- ECG: discrepancies in ST-T waves in stress ECG
- skin has a pale, greyish-yellow discoloration
Blood:
- ALAT: 45 U/L
- ASAT: 52 U/L
- ALP: 120 U/L
- creatinine: 180 µmol/L
- albumin: 44 g/L
- Ca²⁺: 2.2 mmol/L
- PO₄³⁻: 2.8 mmol/L
- 25(OH) vitamin D: 16 ng/mL (low)
- PTH: 98 ng/L (high)
Key Quotes & What They Tell Us
| Quote / Value | Interpretation |
|---|---|
| “receiving hemodialysis for 15 years”; creatinine 180 µmol/L | Long-standing chronic kidney disease — the root of the bone–mineral disorder |
| PO₄³⁻ 2.8 mmol/L (high); Ca²⁺ 2.2 mmol/L (low-normal) | Failing kidneys retain phosphate; low/low-normal calcium → stimulus for PTH |
| 25(OH) vitamin D 16 ng/mL (low) | Reduced activation of vitamin D (impaired renal 1α-hydroxylation) → less calcium absorption |
| PTH 98 ng/L (high) | Secondary hyperparathyroidism — the parathyroids overwork to correct low calcium |
| “chest pain (angina)”; stress-ECG ST-T changes | Coronary ischaemia — accelerated atherosclerosis/vascular calcification in CKD and diabetes |
| “pale, greyish-yellow discoloration” of skin | Uraemic skin pigmentation typical of chronic renal failure |
Key Points
- Diagnosis: Chronic kidney disease–mineral and bone disorder (renal osteodystrophy) with secondary hyperparathyroidism.
- Pathophysiology: CKD → phosphate retention + reduced active vitamin D → hypocalcaemia → compensatory rise in PTH → bone disease.
- Contrast with primary hyperparathyroidism: Here calcium is low/normal and phosphate is high (the reverse of the primary form).
- Cardiovascular link: Phosphate/calcium imbalance promotes vascular calcification → coronary disease (angina).
- Aggravating factors: Type 2 diabetes and 15 years of dialysis.
一問一答
▶How does the calcium/phosphate pattern of secondary hyperparathyroidism differ from primary?
Secondary: low/normal calcium with high phosphate; primary: high calcium with low phosphate (the reverse).
▶Why is active vitamin D reduced in CKD?
Failing kidneys cannot perform 1α-hydroxylation, so less active vitamin D is produced → reduced gut calcium absorption.
▶In the Case 3 patient (15 years dialysis, high phosphate, low-normal calcium, high PTH), what is the diagnosis?
Chronic kidney disease–mineral and bone disorder (renal osteodystrophy) with secondary hyperparathyroidism.
▶What is the pathophysiology of secondary hyperparathyroidism in CKD?
CKD causes phosphate retention plus reduced active vitamin D → hypocalcemia → compensatory rise in PTH → bone disease.
▶Why does the patient have angina and ischemic ECG changes in Case 3?
Accelerated atherosclerosis and vascular calcification from CKD and diabetes cause coronary ischemia.
▶How does phosphate/calcium imbalance promote cardiovascular disease in CKD?
It promotes vascular calcification, accelerating atherosclerosis and coronary disease (angina).
▶What causes the pale, greyish-yellow skin discoloration in Case 3?
Uremic skin pigmentation typical of chronic renal failure.
▶Why does phosphate accumulate in CKD?
Failing kidneys cannot excrete phosphate adequately, causing hyperphosphatemia.
▶How does hyperphosphatemia lower serum calcium in CKD?
Excess phosphate binds calcium and suppresses active vitamin D, reducing calcium absorption and lowering serum calcium.
▶Why is PTH elevated (98 ng/L) in Case 3?
Chronic hypocalcemia and high phosphate stimulate the parathyroids to overproduce PTH (secondary hyperparathyroidism).
▶What is renal osteodystrophy?
The spectrum of bone disease caused by CKD-mineral and bone disorder, driven by secondary hyperparathyroidism, phosphate retention, and vitamin D deficiency.
▶How does long-standing dialysis contribute to bone-mineral disorder?
Persistent CKD over years sustains phosphate retention, low active vitamin D, and high PTH, progressively damaging bone.
▶What is the role of FGF23 in CKD-mineral bone disorder?
Rising FGF23 promotes phosphate excretion early but also suppresses active vitamin D, contributing to secondary hyperparathyroidism.
▶How does type 2 diabetes aggravate the picture in Case 3?
It is the underlying cause of CKD and adds to accelerated atherosclerosis and cardiovascular risk.
▶What are the mainstays of managing CKD-mineral bone disorder?
Phosphate binders and dietary phosphate restriction, active vitamin D/analogues, and calcimimetics to control PTH.
▶Why is creatinine elevated (180 µmol/L) despite dialysis?
Dialysis only partially clears waste; residual renal failure keeps creatinine elevated.
▶What can prolonged secondary hyperparathyroidism eventually become?
Tertiary hyperparathyroidism — autonomous PTH secretion with hypercalcemia despite correction of the original stimulus.
▶Why does excess PTH weaken bone in renal osteodystrophy?
High PTH increases osteoclastic bone resorption (osteitis fibrosa cystica), reducing bone strength.
▶Why is cardiovascular disease the leading cause of death in dialysis patients?
Vascular calcification, hypertension, dyslipidemia, and uremic factors accelerate atherosclerosis and cardiac events.
▶What stress-test finding suggested coronary ischemia in Case 3?
ST-T wave changes on the stress ECG.