Osteomalacia: qualitative defect of bone with abnormal softening of the bone due to deficient mineralization of osteoid (immature bone) secondary to inadequate amounts of calcium and phosphorus
Rickets: the same disease occurring in children which has subsequent effects on the growing skeleton
Aetiology
The principal causes of osteomalacia and rickets involve either insufficient calcium absorption, or phosphate deficiency caused by increased renal losses
Vitamin D deficiency - malnutrition/malabsorption, lack of sunlight exposure
Hypophosphateamia
Re‐feeding syndrome
Alcohol abuse - impairs phosphate absorption
Malabsorption
Renal tubular acidosis
Long term anticonvulsant use
Chronic kidney disease - reduced phosphate resorption and failure of activation vitamin D, resulting in secondary hyperparathyroidism
Some renal diseases are inherited disorders (X‐linked hypophosphataemia or vitamin D resistant rickets)
Pathophysiology
Vitamin D deficiency
Vitamin D stimulates absorption of calcium from GI tract, kidney and bone, also iduces osteoblasts to release osteocalcin
Vitamin D deficiency leads to hypocalcaemia and elevated PTH
This increases calcium absorption, osteoclastic activity, and release of Ca2+ from bone
Results in impaired mineralisation of newly formed osteoid (thick osteoid seams)
Bone is weakened - prone to fracture (micro-fractures or gross fractures)
Clinical presentation
Symptoms
Bone pain - pelvis, spine and femora
Symptoms of hypocalcaemia - paraesthesiae, muscle cramps, irritability, fatigue, seizures, brittle nails
Sustain pathological fractures easily
Signs
Deformities from soft bones (particularly in rickets)
Proximal myopathy
Dental defects (caries, enamel)
Investigations
X-ray - pseudofractures (aka Looser’s zones), particularly of the pubic rami, proximal femora, ulna and ribs, poor cortico-medullary differentiation
Bloods - ↓ calcium and serum phosphate, ↑ serum ALP
Management
Involves vit D therapy with calcium and phosphate supplementation
D3 tablets (400-800IU per day after loading with 3200IU per day for 12 weeks) - calcitriol (1-25 dehydroxycholecalciferol), alfacalcidol (1⍺ hydroxycholecalciferol)
Combined vitamin D and calcium tablets e.g. adcal D3
Considerations for chronic renal disease
Patients may have a very high 25-OH vitamin D so make sure to check 1-25 OH vitamin D
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