Makindo Medical Notes.com

Related Subjects: |Vitamin D Replacement |Osteomalacia-Rickets-Vitamin D |Vitamin D resistant rickets |Vitamin D (25 OH D) Testing |X linked Hypophosphataemic rickets |Osteoporosis

Phosphate binds to calcium and both are needed along with Vitamin D for strong bones and teeth.

About

• Impaired mineralisation of newly formed bone matrix or osteoid.
• The bones are soft with poor growth and weak and painful
• Rickets is impaired mineralisation at the epiphyseal growth plate in children.
• Osteomalacia is a disease of adults after epiphysis fuse

Aetiology

• Vitamin D is a fat-soluble vitamin found mainly in Dairy, oily fish and eggs.
• Vitamin D also comes from sunlight on the skin
• Can be due to lack of Vitamin D, Calcium and Phosphate
• Occasionally it is a genetic and inherited condition
• Commoner in those with dark skin

Pathology

• Rickets : poor mineralization of the epiphyseal growth plate cartilage in children, resulting in skeletal deformities and growth retardation
• Osteomalacia: poor mineralization of the underlying mature organic bone matrix (osteoid) following growth plate closure in adults

History

• In 1645, Daniel Whistler described the "English disease" of Rickets
• Osteomalacia is derived from Greek: osteo- which means "bone", and malacia which means "softness

Causes

• Vitamin D deficiency: raised PTH and low PO4. Dietary loss, lack of sunlight and skin cover. Binders that reduce uptake.
• Renal osteodystrophy: Renal failure leads to failure to make 1,25-dihydroxy-cholecalciferol
• Vitamin D resistant rickets due to mutations in Vitamin D receptor gene. May respond to high doses of Vitamin D
• Malabsorption: No fat-soluble vitamins: Gastrectomy, cystic fibrosis, coeliac disease, Crohn disease and primary biliary cirrhosis
• Renal causes renal phosphate, multiple myeloma and Fanconi syndrome. Proximal (type 2) RTA.
• Drug-induced: Anticonvulsants may induce liver enzymes e.g. Phenytoin, leading to an increased breakdown of 25-hydroxy-vitamin
• Liver disease: Due to reduced hydroxylation of vitamin D to 25-hydroxy-cholecalciferol
• Tumour-induced osteomalacia: Mediated by raised tumour production of phosphatonin fibroblast growth factor 23 (FGF-23) which causes hyperphosphaturia. Low PO4. Often causes myalgia and weakness
• X linked hypophosphataemia

Clinical

• Rickets
  • Seen in children, Growth retardation, hypotonia
  • Apathy in infants. Appear Ill. Shortened height
  • 'Rickety rosary' due to rib deformities
  • Harrison's sulcus due to chest wall deformity
  • Bowed legs, Dental problems weak tooth enamel
  • Craniotabes with deformed skull
  • Once weight bearing - knock-kneed, bow-legged
  • Deformities of the metaphyseal/epiphyseal junction (eg the rachitic rosary).
• Osteomalacia
  • Proximal Muscle weakness and bone pain
  • Bones ache and can be tender to press on the sternum
  • Waddling gait due to low phosphate and difficult sitting to stand
  • Hypocalcaemic tetany can be seen as well as signs of hypocalcaemia
  • Fragile bones and Fractures may occur. There may be hypotonia.

Differentials in Adults

• Osteoporosis
• Paget's disease
• Bone deformity due to Congenital Syphilis in children

Investigations

• ↓ calcium ↓ phosphate
• ↑ alkaline phosphatase in 90%
• ↓ Parathyroid hormone ( secondary to low Ca)
• ↓ Serum 25 (OH) D3 < 25 nmol/L (10 ng/mL)
• ↑ Serum FGF-23 causes phosphate loss and tumour -induced osteomalacia.
• If RTA suspected VBG show hyperchloremic acidosis and normal anion gap
• Plain films: reduced mineralisation and pseudofractures which appear as narrow sclerotic lines at right angles to the cortex usually in the femur and pelvis. These are famously called Looser's zones and are incomplete stress fractures that heal with callus which is lacking in calcium due to poor mineralisation. They can be seen as translucent bands perpendicular to the bone cortical surface. Usual sites for Looser's zones are at points of stress such as Pubic rami, Humeral neck, Femoral neck and Lateral borders of scapulae
• Biopsy: Bone biopsy if one shows incomplete mineralization.

Prevention

• Pregnant and breastfeeding women should consider taking a daily supplement containing 10 micrograms (mcg) of vitamin D from at least October to March
• Babies from birth to 1 year of age, whether exclusively or partially breastfed, should be given a daily supplement containing 8.5 to 10mcg of vitamin D, to make sure they get enough
• Babies fed infant formula do not need a vitamin D supplement until they are receiving less than 500ml (about a pint) of infant formula a day, because infant formula is fortified with vitamin D
• Children aged 1 to 4 years old should be given a daily supplement containing 10mcg of vitamin D

Management

• Ensure a diet adequate in calcium and phosphate and Vitamin D and exposure to sunlight when possible. Replace whichever is deficient in the diet
• Vitamin D
  • Calciferol (vitamin D2/D3) 50 000 units/week PO for 3 months
  • Calciferol IM 300 000 units x 2. Give children adjusted doses.
• Maintain Vitamin D: Long term 800-1000 units of vitamin D per day.
• Oral calcium of 1000 to 1200 mg/day.
• If due to renal disease or vitamin D resistance, give alfacalcidol (1alpha-hydroxyvitamin D3 250ng- 1mcg daily, or calcitriol (1,25-dihydroxy-vitamin D3) 250ng-1mcg OD adjust dose according to plasma Ca²⁺.Alfacalcidol and calcitriol can cause dangerous hypercalcaemia.
• Tumour-induced osteomalacia: treat the tumour which may be benign.
• X linked hypophosphataemia: oral phosphate and 1,25(OH)2 Vitamin D

References

• Vitamin D guidelines
• NHS guidelines