Osteomalacia

Question 1

Define Osteomalacia

Answer 1

Metabolic bone disease characterise by incomplete mineralisation of the underlying mature bone matrix (osteoid) following growth plate closure in adults

Question 2

Define Rickets

Answer 2

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

Question 3

Aetiology of Osteomalacia

Answer 3

Vitamin D deficiency (sub-optimal UV-B sunlight exposure | sunscreen use | insufficient dietary supplementation | inability of the SI to absorb dietary sources (gastrectomy, coeliac, bariatric weight loss))

Acquired:
Nutritional deficiency (vit D, phosphorus, calcium)
Drug (anticonvulsants)
Liver disease
Chronic kidney disease, hypoparathyroidsim
Renal osteodystophy /CKD-MBD)
Mineralisation inhibitors (bisphosphonates, fluoride)
Tumour induced

Inherited:
Rickets
Hypophosphataemia

Mixed:
Fanconi’s syndrome
Renal tubular acidosis

Question 4

Symptoms of Rickets and Osteomalacia

Answer 4

Rickets:
Growth retardation
Short stature.
Costochondral junction swelling

Osteomalacia:
Bone pain (diffuse, usually localised to lower extremities, lower spine, ribs, pelvis)
Malaise
Hx of fractures

Question 5

Signs of Rickets and Osteomalacia

Answer 5

Rickets:
Softening of bone -> deformities (bowed legs, knock knees)
Bossing of frontal and parietal bones
Hypotonia
Costochondral junction swelling (rickets)

Osteomalacia:
Proximal myopathy
Waddling gait
Hypocalcaemia (Trousseau’s, Chvostek’s)

Question 6

Investigations for osteomalacia

Answer 6

Serum calcium: normal (secondary hyperPTH) or low
Serum 25-hydroxyvitamin D: low <25
Serum phosphate: low

U+Es: Urea and creatinine ratio elevated
Intact PTH: raised
Serum alk phos: Raised
24h urinary calcium and phosphate: low calcium, high phosphate

Bone X-rays:
Subperiosteal region resorption at the phalanges
Bone cysts
Resorption of the distal end of long bones
Reduced bone density and cortex thinning
Osteopenia
Coarse trabeculae
Codfish vertebrae
Looser pseudofractures
CKD-MBD: osteosclerosis

DXA: low bone density
Iliac
Iliac crest biopsy: reduced distance between tetracycline bands

Question 7

Management for vitamin D deficiency

Answer 7

1. Calcium and vit D supplements (ergocalciferol PO, calcium carbonate PO)
2. Calcium + vit D metabolite (calcitriol PO + calcium carbonate PO)

Increase dose of vit D if on anticonvulsants, glucocorticoids
Renal failure -> alfacalcidol

Question 8

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

Answer 8

Calcium + vitamin D metabolite + phosphate

Calcitriol (PO)
Sodium phosphate/potassium phosphate (PO)
Calcium carbonate (PO)

Question 9

Complications of Osteomalacia

Answer 9

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