Bone disease

Vitamin D deficiency results in myopathy (proximal weakness) and musculoskeletal aches and pains, limping and children are often miserable. Rickets can result in classical signs of bow legs and swollen joints. Radiographs may show widened metaphyses. The causes may be due to malabsorption (e.g., coeliac disease, inflammatory bowel disease), dietary deficiency, inadequate sun exposure, renal disease and drugs (e.g., antiepileptic drugs). There are also inherited forms. 

Investigations include bone chemistry (serum calcium, phosphate, alkaline phosphatase, parathyroid hormone and 25 hydroxy vitamin D).  The threshold for vitamin D deficiency in asymptomatic individuals is controversial.

Insufficiency and deficiency in vitamin D is common in all populations but more common in developing countries especially in climates where exposure to the sun is less due to the hot weather such as in hot climates. In United Arab Emirates, for example, 19.7% of adolescents were vitamin D deficient and 45% were vitamin D insufficient. Percentages were higher in females than in males. Definitions of insufficiency and deficiency are based on the levels of 25 hydroxy vitamin D where sufficiency is defined as levels > 50 micromol/litre, insufficiency as levels between 30 and 50 micromol/litre and deficiency for levels < 30 micromols/litre. 

Risk factors to Nutritional Rickets:

• Maternal vitamin D during pregnancy: When a mother has low vitamin D, the supply transferred to the foetus will be low and the born baby will have higher risk of developing rickets. In fact, in babies born to mothers with severe vitamin D deficiency during pregnancy, the manifestations of rickets can appear even before the typical age of 3 months.
• Breastfeeding: Unless the breastfeeding mother is receiving high doses of vitamin D supplements (higher than 2000IU daily), the supply of vitamin D in breast milk is typically less than 25 IU per litre. In developed countries, infants’ main reason for deficiency in vitamin D are prolonged breastfeeding and limited exposure to sunlight.
• Skin pigmentation and exposure to sunlight: Dark skinned individuals produce less vitamin D in response to sunlight compared to fair skinned individuals. Breast milk of dark skinned mothers, thus, has less vitamin D than lighter skinned ones and indeed dark skinned mothers are at higher risk of having deficiency themselves reducing the amount of vitamin D transferred to the foetus prenatally.
• Other causes: Any malabsorptive disorder including exocrine pancreatic deficiency like cystic fibrosis, gastrectomy, major bowel resection, coeliac disease and inflammatory bowel disease may lead to reduced absorption of vitamin D and higher risk for deficiency. Certain anticonvulsants and the antiviral drugs used in treatment of HIV lead to vitamin D deficiency by enhancing the catabolism of 25 hydroxy vitamin D and 1,25 dihydroxy vitamin D.

Clinical features 

• Delayed closure of the fontanelles. Parietal and frontal bossing. Craniotabes (soft skull bones).
• Enlargement of the costochondral junction visible as beading along the anterolateral aspects of the chest (the "rachitic rosary").
• Formation of Harrison sulcus (or groove) at the lower margin of the thorax caused by the muscular pull of the diaphragmatic attachments to the lower ribs.
• Widening of the wrist and bowing of the distal radius and ulna.
• Progressive lateral bowing of the femur and tibia. The lower extremities tend to be predominantly affected in the heritable forms of phosphopenic rickets.
• Decreased muscle tone and delay in motor developmental milestones. Hypocalcemic seizures can be the presentation of severe rickets in the first year of life. Children with calcipenic rickets have reduced immunity and are prone to recurrent infections.

Radiological changes are often seen at the growth plates. Widening of the epiphyseal plate is one of the earliest radiological signs in rickets. As the disease progresses, other signs like cupping, splaying and stippling of the growth plates start to appear. In severe rickets, pathological fractures and looser’s zones (pseudofractures) may be seen.

Treatment: Daily doses of Vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol). Levels of calcium, phosphorus and alkaline phosphatase should be measured every four weeks after starting treatment for the first three months. By four weeks, levels of calcium and phosphorus are expected to normalize and alkaline phosphatase starts going down to reference ranges. Radiographs should be repeated after 3 months of treatment to see evidence of healing. Further investigation (for other causes of rickets or states of malabsorption) is needed if there is no improvement by 3 months.

Prevention: American Academy of Pediatrics recommends that exclusively breastfed infants should receive 400-600 IU of vitamin D supplementation until full weaning to sources that provide vitamin D or to a fortified formula.