Osteomalacia

Question 1

Define osteomalacia and rickets

Answer 1

Metabolic bone disease characterised by incomplete mineralisation of the underlying mature organic bone matrix (Osteoid) following growth plate closure in adults

Rickets = metabolic bone disease characterised by defective mineralisation of the epiphyseal growth plate cartilage in children, resulting in skeletal deformities and growth retardation

Question 1

Aetiology of osteomalacia

Answer 1

Vitamin D deficiency, due to:
- Sub-optimal UV-B sunlight exposure + use of sunscreen (esp. in the UK)
- Insufficient dietary supplementation
- Malabsorption: Gastrectomy, Coeliac disease, Bariatric weight loss surgeries

Acquired
- Nutritional deficiency i.e. vit D, phosphorus, calcium deficiency, malabsorption, lack of UV-B
- Drug -induced e.g. anticonvulsants, bisphosphonates, fluoride
- Liver disease, Drugs (anticonvulsants) (25-hydroxylation of vitamin D)
- Chronic kidney disease (Renal osteodystrophy), Hypoparathyroidism (Reduced 1𝝰-hydroxylation)
- Receptor defects
- Tumour-induced: paraneoplastic syndrome of renal phosphate wasting

Inherited
- Vit D-dependant Rickets: type 1 and 2
- Hypophosphataemia: inborn error of metabolism
- Hypophosphataemic rickets: X-;inked hypophosphataemia
Mixed: Fanconi’s syndrome and renal tubular acidosis

Question 2

Clinical features of osteomalacia

Answer 2

Rickets
Growth retardation, short stature
Costochondral junction swelling
Bowed legs
Widened epiphyses of the wrist
Myopathy → wadlling gait

Osteomalacia
Bone pain (diffuse, usually lower extremities/lower spine/ribs/pelvis
Malaise
Hx fracture
Looser’s zones (Pseudofractures that will not break until under pressure/trauma)
proximal myopathy → waddling gait
Hypocalcaemia → Trousseau’s + Chvostek’s

Question 3

Investigations for osteomalacia

Answer 3

24h urinary Calcium and phosphate: low calcium high phosphate

Serum 25-hydroxyvitamin D: low
Bone profile: calcium normal/low | phosphate low
U&Es: Ur/Cr ratio elevated
PTH: raised
Serum ALP: raised

Bone X-ray:
- Looser pseudofractures
- Bone cysts
- Osteopenia
- Reduced bone density and cortex thinning
- Codfish vertebrae
DEXA: low bone density
Iliac crest biopsy: rarely used

Question 4

Management for osteomalacia

Answer 4

Vitamin D deficiency
Calcium + vitamin D supplements
- Ergocalciferol 50,000 units orally once or twice weekly f r 6-12 week AND Calcium carbonate 1-2g/day orally in 3-4 divided doses

Second line
Calcium + vitamin D metabolite
- Calcitriol 0.25-1 microgram orally once daily AND Calcium carbonate 1-2g/day orally in 3-4 divided doses

Note: if on anticonvulsants, glucocorticoids etc., increase the dose of vitamin D
Note: if in renal failure (no 1-alpha hydroxylation) - give alfacalcidol

Question 5

Management for Inherited or acquired disorders of phosphate wasting/oncogenic osteomalacia

Answer 5

Calcium + vitamin D metabolite + phosphate

Calcitriol + sodium phosphate + calcium carbonate

Question 6

Complications of osteomalacia

Answer 6

Insufficiency fractures or pseudofractures
Secondary hyperparathyroidism
Metastatic calcification in renal failure
Hypercalcaemia
Hypercalciuria and kidney stones