Introduction

These are essentially the same disorder. In children, the disease is rickets but after fusion of the epiphyseal plates it is known as osteomalacia.
The most common cause is vitamin D deficiency.
The condition is characterised by normal bone formation with abnormal bone mineralisation, thus there is excess osteoid and cartilage, and insufficient bone.

Causes

  • Vitamin D deficiency – due to lack of sunlight ± insufficient dietary intake. Both often occur simultaneously. Common in the elderly (e.g. often indoors for long periods) and also in dark skinned populations residing in non-native climes (e.g. in the UK) – particularly if they cover up their skin (e.g. common in Inidan Pakistani women and girls in the UK. As a result, chapatti flour is fortified with vitamin D).
  • Renal osteomalacia – resulting in vitamin D deficiency. Often occurs in patients with long-term renal pathologies.
  • Drug Induced – particularly with anticonvulsants
  • Vitamin D resistant rickets / osteomalacia – a collection of inherited diseases, including familial hypophosphataemia, and a disorder where the vitamin D receptor is defective.
    • Type I hereditary vitamin D-dependent rickets – caused by ineffective conversion of vitamin D precursors in the kidneys (25()H)D to 1,25(OH)D. Autosomal recessive
    • Type II hereditary vitamin D-dependent rickets – due to mutations in the 1,25(OH)D receptor, causes end-organ resistance to vitamin D
    • Both are treated with high levels of calcitriol ( 1,25()H)2vitamin D )
  • Hypoparathyroidism
  • Low dietary calcium / phosphate (rare)

 

Clinical Features

  • Muscle aches
  • Muscle weakness
  • Bone Pain / pain on walking
  • Predisposition to fractures – especially in the elderly
  • Tetany – parasthesia of the lips, tongue and face, sometimes facial and carpopedal spasm, rarely seizures. May be hard to distinguish from other causes of seizure.

In children

  • Generally unwell
  • Delayed walking / crawling / sitting
  • In pregnancy, amy affect the foetus, especially the skull of the newborn (pingpong ball like skull – craniotabes)
    • Craniotabes is also seen in syphilis, and neonates with this are often tested for the disease.
  • Rachitic Rosary – bead like nodules on the ribs
  • Kyphoscoliosis
  • Bowed legs and ‘knock knees’ only occur in severe cases in older children

 

Investigations

Vit D – often ↓
Alkaline phosphate: may be ↑ or ↔
Parathyroid hormone ↑
↓Calcium

  • Low vitamin D results in low absorption of calcium in the diet, which inturn stimulates increased PTH production. High levels of PTH also increase phosphate excretion, but may normalise serum calcium levels.

↓Phosphate
Renal failure (in renal osteomalacia)
X-ray – usually of radius / ulnar

  • Diagnosis cannot be made with X-ray alone – also need PHT and 25(OH)D level to rule out other causes of demineralisation.
  • Rickets
    • Changes most easily seen at the ends of the radius and ulnar
    • Ragged bone edges
    • Apparent increased distance from arm bones to carpal bones (Due to demineralisation of this area).
    • Fuzzy, cup-shaped diaphyses (ends of the bone)
    • General increase in radiolucency of the bone
  • Osteomalacia
    • Reduced amount of cortical bone
    • Partial fractures

Treatment

Vitamin D supplements + calcium are first line – 400U tablets, 1-2 times/day

  • After 3 weeks, x-ray improvements can be seen. Typically starting at the very tip of the bone, and continuing down through the affected segment
  • Malapborption might require calciferol (1,25(OH)2D) – 1mg/day (equivalent to 40,000 units of Vit D!)
  • Vit-D resistant rickets should be treated with calciferol 10,000 unites/day
  • Renal osteomalacia is best treated with alfacalcidol
  • Hypercalcaemia is common with all vit D treatments, especially alfacalcidol.

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