Bone in hyperparathyroidism and renal osteodystrophy
- Lesion
Too much parathyroid hormone makes osteoclasts tunnel through bone. Kidney failure adds phosphate retention, low vitamin D and several bone patterns.
What it is
Parathyroid hormone acts on osteoblasts, which signal osteoclasts through RANKL. When PTH is high for a long time, as in primary hyperparathyroidism or the secondary hyperparathyroidism of chronic kidney disease, resorption accelerates. Mild disease causes only osteopenia; long-standing severe disease produces osteitis fibrosa cystica, with dissecting resorption, marrow fibrosis, cysts and brown tumours. Renal osteodystrophy is the full set of skeletal changes of chronic kidney disease: high-turnover bone from secondary hyperparathyroidism, low-turnover adynamic bone, osteomalacia and mixed patterns, together called CKD–mineral and bone disorder.
Structure
- Dissecting osteitis: osteoclasts tunnel along the centre of trabeculae, which look like railroad tracks.
- The marrow next to trabeculae is replaced by loose fibrovascular tissue (peritrabecular fibrosis).
- Brown tumour: multinucleated giant cells in a vascular, fibroblastic stroma with haemosiderin and red cells; gross brown colour.
- Cortical thinning and subperiosteal erosion on X-ray; 'salt and pepper' skull and loss of the lamina dura around teeth.
- Adynamic bone: thin trabeculae with few osteoblasts and osteoclasts and no osteoid excess.
Step by step
- Primary: a parathyroid adenoma, hyperplasia or carcinoma secretes PTH autonomously.
- Secondary (kidney failure): falling nephron mass retains phosphate and lowers calcitriol; FGF23 rises and klotho falls.
- Low calcium and calcitriol and high phosphate push the parathyroids to hypertrophy and secrete more PTH.
- High PTH raises osteoblast RANKL, osteoclasts multiply and resorption outpaces formation.
- Bone is replaced by fibrous tissue, cysts and haemorrhagic giant-cell masses: osteitis fibrosa cystica.
- In kidney failure, acidosis, low vitamin D and treatment effects add osteomalacia or low-turnover adynamic bone.
Bone patterns in chronic kidney disease
| Pattern | Turnover | Mechanism | Biopsy |
|---|---|---|---|
| Osteitis fibrosa (hyperparathyroid bone) | High | Secondary hyperparathyroidism | Many osteoclasts, tunnelling, marrow fibrosis |
| Adynamic bone disease | Low | Over-suppressed PTH, diabetes, aluminium | Few cells, little osteoid |
| Osteomalacia | Low | Low calcitriol, acidosis, aluminium in the past | Wide unmineralized osteoid seams |
| Mixed uraemic osteodystrophy | Variable | Several mechanisms together | Features of high turnover plus defective mineralization |
Clinical notes
- Classic phrase for symptomatic primary hyperparathyroidism: bones, stones, abdominal groans and psychic moans.
- Kidney failure patients have bone pain and fractures, and the same mineral disorder calcifies vessels and soft tissue (calciphylaxis).
- A giant-cell lesion of the jaw or long bone in a patient with high calcium should prompt measurement of PTH before surgery.
In the lab
- Primary: high calcium, low or normal phosphate, high PTH.
- Secondary (CKD): low or normal calcium, high phosphate, high PTH, high FGF23; alkaline phosphatase rises with high turnover.
Test yourself
Think of the answer, then tap the question to see it.
How does PTH activate osteoclasts?
Indirectly: it acts on osteoblasts, which express RANKL and drive osteoclast formation and activity.
What is a brown tumour?
A reactive mass of osteoclast-type giant cells, fibrous tissue and old haemorrhage in hyperparathyroidism.
Why does chronic kidney disease cause secondary hyperparathyroidism?
Phosphate retention, low calcitriol, high FGF23 and low calcium stimulate the parathyroid glands.
What is adynamic bone disease?
A low-turnover bone disease in CKD with few bone cells, often from over-suppression of PTH.
Elsewhere in DurgiPedia
- Calcium regulation: PTH, vitamin D and calcitonin
- Phosphate and FGF-23
- Renal handling of calcium, phosphate and magnesium
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Hyperparathyroidism: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Primary Hyperparathyroidism (StatPearls (NCBI Bookshelf), 2025); Chronic Kidney Disease (StatPearls (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.