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OutiMäkitie

Rickets

Essentials

  • Rickets is a disorder of bone mineralization usually caused by vitamin D deficiency.
  • Risk groups include e.g. breastfed infants, children with milk allergy as well as sedentary and dark-skinned children.
  • In rickets, the plasma concentration of calcium may be either low or normal, plasma phosphate concentration is decreased and the plasma concentrations of parathyroid hormone and alkaline phosphatase are usually increased.
  • Diagnosis is based on the clinical picture and the typical radiological and laboratory findings.

Aetiology

  • Deficiency of vitamin D is by far the most common cause.
    • Insufficient exposure to sunlight
    • Insufficient dietary intake of vitamin D
    • Malabsorption; untreated coeliac disease
  • Risk groups include
    • infants that are solely or mostly breastfed
    • children with milk allergy
    • families with a negative attitude towards vitamin supplements (and often also vaccinations) in countries where vitamin D supplementation is recommended
    • dark-skinned immigrant children (whose need for vitamin D is particularly great) in countries with a restricted amount of sunshine.
  • Rare causes of rickets
    • Disturbed metabolism of vitamin D (e.g. a defect in 1-hydroxylation in association with renal insufficiency, a defect in 25-hydroxylation in association with a liver disease, resistance of target organs to vitamin D)
    • An adverse effect of certain medicines; phenytoin, isoniazid, ketoconazole
    • Deficiency of phosphate (hereditary hypophosphataemic rickets, Fanconi's syndrome)

Calcium metabolism in rickets

  1. The hypocalcaemic phase usually lasts for a few days, but at the age of 2-9 months it might become prolonged and result in tetany and convulsions.
  2. The phase of secondary hyperparathyroidism, normocalcaemia and hypophosphataemia
    • As the vitamin D deficiency continues, hyperparathyroidism develops and hypocalcaemia is temporarily reversed by the release of calcium from the bones and by the decreased urinary excretion of calcium, but at the same time phosphaturia and hypophosphataemia develop.
  3. The phase of hypocalcaemia and severe bone disease, with associated growth retardation, bone deformities and increased bone fragility as well as increased tendency for infections and muscle weakness.
    • As the body's calcium stores are depleted, hypocalcaemia and bone disease will develop during chronic hyperparathyroidism. At this stage bone changes are evident in x-rays.

Diagnosis

  • Suspect rickets if the child has not been given prophylactic vitamin D (ask actively about the history of vitamin D administration) or the growth in height is retarded especially in a child belonging to some of the risk groups mentioned above.
  • Clinical presentation
    • Symptoms associated with hypocalcaemia (tetany, convulsions)
    • Bone abnormalities and growth disturbance (rachitic rosary of the costochondral junctions, growth disturbance at the distal epiphyses, a downward shift in the growth pattern, retarded psychomotor development, muscular hypotonia); susceptibility to infections
  • Radiology
    • Typical changes in metaphyses (wrists [picture 1], ankles, knees), or rachitic rosary of the costochondral junction seen in lateral chest x-rays
  • Laboratory findings
    • Increased plasma alkaline phosphatase and parathyroid hormone, normal or decreased plasma calcium, decreased plasma phosphate
    • If plasma alkaline phosphatase is increased without hypocalcaemia and/or hypophosphataemia, the child may have incipient rickets, and the plasma parathyroid hormone concentration will be found increased.
    • Low serum 25(OH)D concentration in vitamin D deficiency
    • Small children may have a transient increase in the alkaline phosphatase concentration with unknown aetiology. The concentration is usually spontaneously normalized within a few weeks or months but follow-up is required.
    • An increase in the alkaline phosphatase concentration may be found in healthy children during the phase of rapid growth, e.g. in puberty. This is caused by an increase in bone metabolism, which is also seen during growth hormone therapy. A specialist consultation is recommended.

Differential diagnosis

  • Rule out the following:
    • renal insufficiency
    • malabsorption (coeliac disease)
    • liver disease
    • a transient increase in alkaline phosphatase concentration
    • hypophosphataemic rickets and other hereditary forms of rickets
    • calcium deficiency
    • anticonvulsive medication.

Treatment

  • Vitamin D
    • According to the current knowledge, vitamin D3 should be preferred (the effect is somewhat better than with vitamin D2).
    • The therapeutic dose is 50 µg/day (= 2 000 units/day) in addition to the normal age-adjusted daily intake of vitamin D (as vitamin D3) recommended for rickets prophylaxis.
  • Adequate simultaneous intake of calcium must also be ensured. This is usually achieved if the child consumes 0.5 litres or more of milk products a day. If calcium intake is insufficient or rickets is severe, an oral calcium preparation should be given, 50 mg/kg/day divided in 4 doses, for at least 2 weeks. Thereafter the dosing should be according to response.
  • The treatment of symptomatic hypocalcaemia requires specialist intervention.

Follow-up

  • The treatment response must always be monitored by checking plasma calcium, phosphate and alkaline phosphatase
    • after 2 weeks (alkaline phosphatase may still be on the increase due to fast bone metabolism)
    • after 3 months (also the concentration of parathyroid hormone).
  • Wrist x-rays are repeated 3-6 months after treatment onset. Only if treatment with vitamin D has not brought about improvement or if plasma phosphate concentration will not become normal, further investigations to detect rarer forms of rickets are warranted.