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Rickets

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Overview

Bone mineralisation depends on sufficient amounts of calcium and phosphate and this is maintained by vitamin D. Rickets and osteomalacia describe inadequate bone mineralisation secondary to vitamin D deficiency.

Rickets describes inadequate bone mineralisation in bones before the growth plates have closed and is the term generally used in children. Osteomalacia describes inadequate bone mineralisation after the growth plates have closed and is the term generally used in adults. Rickets and osteomalacia can occur together if the growth plates are open.

Pathophysiology

Insufficient vitamin D leads to inadequate gut absorption of calcium. This leads to the release of parathyroid hormone which activates bone resorption and increases renal phosphate excretion in an attempt to raise serum calcium levels. This combination of decreased calcium and phosphate leads to calcium-deficient rickets.

Phosphate-deficient rickets is also a possible cause. Excess renal phosphate excretion can also lead to rickets, albeit these causes tend to be rare (e.g. Fanconi’s syndrome, phosphate depletion, cadmium and lead poisoning).

Epidemiology

  • In the UK, Vitamin D deficiency is common in both children and adults
  • Globally, nutritional deficiencies are the most common cause of rickets
  • In 2014, the incidence of vitamin D deficiency was 261 per 100,000 person-years
  • Children aged >10 years, who are non-white, and socially deprived are more likely to be vitamin D deficient
  • From 2015-2017, there were 0.48 cases of rickets per 100,000 children

Risk Factors

  • Dietary deficiency in developing countries
  • Darker skin pigmentation (e.g. South Asian or Afro-Caribbean ethnicity)
  • Low or no exposure to the sun
  • Exclusive/prolonged breastfeeding, especially if the mother is vitamin D deficient
  • Using formula milk that is not supplemented with vitamin D

Presentation

Features of rickets include:

  • Impaired growth
  • Bone pain and painful joints
  • Lower limb abnormalities:
    • Genu varum (bow legs) in toddlers
    • Genu valgum (knock knees) in older children
  • Painful wrist swelling
  • Rachitic rosary – painful swelling of the costochondral junctions
  • Craniotabes – skull softening, frontal bossing, and delayed fontanelle closure
  • Delayed tooth eruption
  • Tooth enamel hypoplasia
  • Kyphoscoliosis

Osteomalacia may present with:

  • Persistent bone and muscle pain
  • Proximal muscle weakness
  • Waddling gait

Investigations

Overview

  • Serum 25-hydroxyvitamin D levels:
    • Low
  • Serum calcium and phosphate:
    • Calcium – decreased
    • Phosphate – may be decreased
  • Serum parathyroid hormone (PTH):
    • May be elevated
  • X-ray of long bones:
    • May show a widening of the growth plate

Differential Diagnoses

Blount’s disease

  • This can also present with lower leg angling similar to a bow leg
  • This occurs due to reduced growth plate activity near the inside of the leg while the growth plate near the outside continues to develop normally

Management

Referral

Seek specialist advice or refer to secondary care before starting vitamin D if:

Treatment

Treatment involves vitamin D supplementation and advice regarding safe exposure to sunlight. If dietary calcium is insufficient, calcium supplementation may be needed. 

Monitoring

  • Check serum 25-hydroxyvitamin D and a bone profile after the last dose if a loading vitamin D treatment regimen has been used:
    • If this is below the normal amount or the bone profile is abnormal, a specialist assessment for an underlying cause (e.g. chronic kidney disease) may be necessary

Patient Advice

  • Most people without underlying conditions can have sufficient vitamin D activation if they go out for short periods in the sunlight, wear appropriate sunscreen, and avoid excess and dangerous sun exposure
  • Although it is difficult to maintain sufficient vitamin D from diet alone, some foods can help (such as oily fish, eggs, and some brands of formula milk with vitamin D supplementation)
  • Patients should eat foods that are rich in calcium as well if dietary calcium intake is insufficient

Complications

  • Pathological fractures
  • Slow/impaired growth
  • Skeletal deformities (as mentioned above)
  • Hypocalcaemia
  • Dilated cardiomyopathy – very rare but serious

Prognosis

  • Rickets and osteomalacia generally respond rapidly to vitamin D. There may be an initial increase in bone pain during treatment.
  • Following treatment with vitamin D supplementation, lifelong lifestyle changes and vitamin D supplementation may be needed as it can be difficult to maintain optimum vitamin D levels

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