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.
o 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
o Type II hereditary vitamin D-dependent rickets – due to mutations in the 1,25(OH)D receptor, causes end-organ resistance to vitamin D
o 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
o Generally unwell
o Delayed walking / crawling / sitting
o 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.
o Rachitic Rosary – bead like nodules on the ribs
o Kyphoscoliosis
o 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
o 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
o Diagnosis cannot be made with X-ray alone – also need PHT and 25(OH)D level to rule out other causes of demineralisation.
o 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
o Osteomalacia
§ Reduced amount of cortical bone
§ Partial fractures
Treatment
- Vitamin D supplements + calcium are first line – 400U tablets, 1-2 times/day
o 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
o Malapborption might require calciferol (1,25(OH)2D) - 1mg/day (equivalent to 40,000 units of Vit D!)
o Vit-D resistant rickets should be treated with calciferol 10,000 unites/day
o Renal osteomalacia is best treated with alfacalcidol
o Hypercalcaemia is common with all vit D treatments, especially alfacalcidol.
Notes by Tom Leach
EmoticonEmoticon