Rickets

Rickets is a condition affecting children where there is defective bone mineralisation causing “soft” and deformed bones. In adults the same process leads to a condition called osteomalacia. Osteo– means bone and –malacia means soft.

 

Causes

Rickets is caused by a deficiency in vitamin D or calcium. Vitamin D is either produced by the body in response to sunlight or obtained through foods such as eggs, oily fish or fortified cereals or nutritional supplements. Calcium is found in dairy products and some green vegetables.

There is a rare form of rickets caused by genetic defects that result in low phosphate in the blood. This is called hereditary hypophosphataemic rickets. The most common form is x-linked dominant, however it also has other modes of inheritance.

 

Simplified Pathophysiology

Vitamin D is a hormone (not technically a vitamin) created from cholesterol by the skin in response to UV radiation. Patients with darker skin require a longer period of sun exposure to generate the same quantity of vitamin D. A standard diet contains inadequate levels of vitamin D to compensate for a lack of sun exposure. Reduced sun exposure without vitamin D supplementation leads to vitamin D deficiency.

Patients with malabsorption disorders (such as inflammatory bowel disease) are more likely to have vitamin D deficiency. The kidneys are essential in metabolising vitamin D to its active form, therefore vitamin D deficiency is common in chronic kidney disease.

Vitamin D is essential in calcium and phosphate absorption from the intestines and kidneys. Vitamin D is also responsible for regulating bone turnover and promoting bone reabsorption to boost the serum calcium level.

Inadequate vitamin D leads to a lack of calcium and phosphate in the blood. Since calcium and phosphate are required for the construction of bone, low levels result in defective bone mineralisation. Low calcium causes a secondary hyperparathyroidism as the parathyroid gland tries to raise the calcium level by secreting parathyroid hormone. Parathyroid hormone stimulates increased reabsorption of calcium from the bones. This causes further problems with bone mineralisation.

 

Presentation

Patients with vitamin D deficiency and rickets may not have any symptoms. Potential symptoms are:

  • Lethargy
  • Bone pain
  • Swollen wrists
  • Bone deformity
  • Poor growth
  • Dental problems
  • Muscle weakness
  • Pathological or abnormal fractures

Bone deformities that can occur in rickets include:

  • Bowing of the legs, where the legs curve outwards
  • Knock knees, where the legs curve inwards
  • Rachitic rosary, where the ends of the ribs expand at the costochondral junctions, causing lumps along the chest
  • Craniotabes, which is a soft skull, with delayed closure of the sutures and frontal bossing
  • Delayed teeth with under-development of the enamel

TOM TIP: Think about the risk factors for vitamin D deficiency in your exams and clinical practice. Patients with rickets are likely to have risk factors such as darker skin, low exposure to sunlight, live in colder climates and spend the majority of their time indoors.

 

Investigations

Serum 25-hydroxyvitamin D is the laboratory investigation for vitamin D. A result of less than 25 nmol/L establishes a diagnosis vitamin D deficiency, which can lead to rickets.

Xray is required to diagnose rickets. X-rays may also show osteopenia (more radiolucent bones).

Other investigation results include:

  • Serum calcium may be low
  • Serum phosphate may be low
  • Serum alkaline phosphatase may be high
  • Parathyroid hormone may be high

NICE clinical knowledge summaries suggest additional investigations to look for other pathology:

  • Full blood count and ferritin, for iron deficiency anaemia
  • Inflammatory markers such as ESR and CRP, for inflammatory conditions
  • Kidney function tests, for kidney disease
  • Liver function tests, for liver pathology
  • Thyroid function tests, for hypothyroidism
  • Malabsorption screen such as anti-TTG antibodies, for coeliac disease
  • Autoimmune and rheumatoid tests, for inflammatory autoimmune conditions

 

Management

Prevention is the best management for rickets. Breastfed babies are at higher risk of vitamin D deficiency compared with formula fed babies, as formula feed is fortified with vitamin D. Breastfeeding women and all children should take a vitamin D supplement. NICE clinical knowledge summaries recommend supplements containing 400 IU (10 micrograms) per day for children and young people.

Children with vitamin D deficiency can be treated with vitamin D (ergocalciferol). The doses for treatment of vitamin D deficiency depend on the age (see the BNF). The dose for children between 6 months and 12 years is 6,000 IU per day for 8 – 12 weeks.

Children with features of rickets should be referred to a paediatrician. Vitamin D and calcium supplementation is used to treat rickets.

 

Last updated January 2020
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