Osteomalacia

Question 1

Define osteomalacia

Answer 1

Metabolic bone disease characterised by incomplete bone matrix (osteoid) mineralisation
Rickets – defective mineralisation of epiphyseal growth plate -> skeletal deformities and
growth retardation

Question 2

What are the causes/risk factors of osteomalacia?

Answer 2

• Vitamin D deficiency
- Reduced exposure to sunlight
- Poor diet
- Liver disease
- Chronic kidney disease
- Malabsorption e.g. IBD, coeliac disease, bowel resection
- Receptor defects
• Hypophosphatemia
• Proximal renal tubular acidosis (Fanconi’s syndrome)

Question 3

What are the symptoms of osteomalacia?

Answer 3

• Bone pain
• Weakness
• Malaise
• Fractures

Question 4

What are the signs of osteomalacia?

Answer 4

• Bone tenderness
• Proximal myopathy
• Waddling gait
Rickets
• Bow legs or knock-knees
• Short stature
• Frontal and parietal bossing
• Swelling of costochondral
junctions (rickety rosary)

Question 5

What investigations are carried out for osteomalacia?

Answer 5

• Serum Ca2+ - low or Normal (if secondary hyperparathyroidism acts long enough to counteract the hypocalcaemia cause by hypovitaminosis D).
• PTH - elevated –secondary hyperparathyroidism
• Serum Phosphate - low
• ALP - elevated
• Serum 25-OH D3 - low –exception: Vit D resistence,
• U&Es - may indicate CKD.
• ABG - patients with renal tubular acidosis have normal anion gap hyperchloraemic metabolic acidosis.
• Urinary Phosphate - levated in Phosphate-Wasting Disorders.
• 24-hour Urinary Ca2+ - low; useful in confirming vitamin D-deficient states as a cause of osteomalacia.
• X-Ray - may appear normal or show osteopenia.
Looser’s zones or pseudofractures (radiolucent bands) in ribs, scapula, pubic rami or upper femur.
• Rickets: Cupped, ragged metaphysical surfaces –knee and ankle.
• DEXA Scan - to investigate for osteoporosis and osteopaenia.
• Bone (Iliac Crest) biopsy after double tetracycline labelling - Tetracycline is deposited at the mineralization front as a band. After two courses of tetracycline (separated by a period of days), the distance between the bands of deposited tetracycline is reduced in osteomalacia. Not usually performed as osteomalacia can be diagnosed from the clinical findings

Question 6

What is the management for osteomalacia?

Answer 6

• Vitamin D Replacement: Ergocalciferol and Cholecalciferol. Alfacalcidol (1-hydroxycholecalciferol) for patients with renal failure (as they lack 1a-hydroxylation).
• Calcium Replacement: Calcium carbonate and calcium citrate.
• Treat the underlying cause (e.g. advice on diet and sunlight exposure).
• X-linked hypophosphataemia: Oral phosphate supplements, 1,25-(OH)2 Vitamin D and calcitriol.
• Vitamin D Deficiency: Exists in 2 forms –1a-hydroxylase deficiency and end organ resistance. Both are treated with high dose calcitriol.

Question 7

What are the complications of osteomalacia?

Answer 7

• Bone Deformities  
• Hypocalcaemia: 
- Epileptic Seizures  
- Cardiac Arrhythmias 
- Hypocalcaemic tetany 
- Depression.