Introduction to Rickets

Introduction

Rickets is a disease of growing bone that is unique to children and adolescents. It is caused by a deficiency or impaired metabolism of vitamin D, magnesium, phosphorus or calcium. It leads to softening and weakening of the bones.

Rickets is among the most frequent childhood diseases in many developing countries. The predominant cause is a vitamin D deficiency, but lack of adequate calcium in the diet may also lead to rickets .

Types of Rickets
Different types have been described and may include:

• Nutritional Rickets
• Vitamin D Resistant Rickets
• Vitamin D Dependent Rickets
•  - Type I
•  - Type II
• Congenital Rickets

Pathophysiology
Vitamin D deficiency rickets occurs when the metabolites of vitamin D are deficient. Less commonly, a dietary deficiency of calcium or phosphorus may also produce rickets. Vitamin D-3 (cholecalciferol) is formed in the skin from a derivative of cholesterol under the stimulus of ultraviolet-B light. It is converted into the active metabolite calcitriol after final hydroxylation in the kidney. Calcitriol acts to regulate the body’s calcium metabolism by the following mechanisms:

(1) it promotes absorption of calcium and phosphorus from the intestine; 

(2) it increases reabsorption of phosphate in the kidney; and, 

(3) it acts on bone to release calcium and phosphate. Calcitriol may also directly facilitate calcification. These actions result in an increase in the concentrations of calcium and phosphorus in extracellular fluid.

This increase of calcium and phosphorus in extracellular fluid, in turn, leads to the calcification of osteoid, primarily at the metaphyseal growing ends of bones but also throughout all osteoid in the skeleton. Parathyroid hormone facilitates the 1-hydroxylation step in vitamin D metabolism.

In the vitamin D deficiency state, hypocalcemia develops, which stimulates excess secretion of parathyroid hormone. In turn, renal phosphorus loss is enhanced, further reducing deposition of calcium in the bone.

Etiology
The body needs vitamin D to absorb calcium and phosphorus from food. Rickets can occur if the child’s body doesn’t get enough vitamin D or if his or her body has problems using vitamin D properly.

Lack of vitamin D
There are two sources of vitamin D:
 

1. Sunlight: Skin produces vitamin D when it’s exposed to sunlight. But children in developed countries now tend to spend less time outdoors. They’re also more likely to use sunscreen, which blocks the rays that trigger the skin’s production of vitamin D.

2. Food: Fish oils, fatty fish and egg yolks contain vitamin D. Vitamin D also has been added to some foods, such as milk, cereal and some fruit juices. Children who don’t eat enough of these fortified foods can develop a vitamin D deficiency.

Problems with absorption
Some children are born with or develop medical conditions that affect the way their bodies absorb vitamin D. Some examples include:

• Celiac disease
• Inflammatory bowel disease
• Cystic fibrosis
• Kidney problems

Signs and Symptoms
Signs and symptoms of rickets may include:

• Delayed growth
• Pain in the spine, pelvis and legs
• Muscle weakness
• Generalized hypotonia
• Dental problems

Because rickets softens the growth plates at the ends of a child’s bones, it can cause skeletal deformities such as:

• Bowed legs
• Abnormally curved spine
• Thickened wrists and ankles
• Breastbone projection producing pigeon chest deformity
• Craniotabes (areas of thinning and softening of bones of the skull)
• Harrison’s groove
• Tetany

Diagnosis
Rickets may be diagnosed with the help of:

Blood tests:

• Serum calcium may show low levels of calcium, serum phosphorus may be low, and serum alkaline phosphatase may be high.
• Arterial blood gases may reveal metabolic acidosis.

X-rays of affected bones may show loss of calcium from bones or changes in the shape or structure of the bones.

Bone biopsy is rarely performed but will confirm rickets.

Management
Diet and sunlight

Treatment involves increasing dietary intake of calcium, phosphates and vitamin D. Exposure to ultraviolet B light (sunshine when the sun is highest in the sky), cod liver oil and halibut-liver oil, and also good sources of vitamin D.

A sufficient amount of ultraviolet B light in sunlight each day and adequate supplies of calcium and phosphorus in the diet can prevent rickets. Darker-skinned people need to be exposed longer to the ultravoilet rays. The replacement of vitamin D has been proven to correct rickets using these methods of ultraviolet light therapy and medicine.

Vitamin D therapy
Treatment for rickets may be administered gradually over several months or in a single-day dose of 15,000 mcg (600,000 U) of vitamin D. If the gradual method is chosen, 125-250 mcg (5000-10,000 U) is given daily for 2-3 months until healing is well established and the alkaline phosphatase concentration is approaching the reference range. Because this method requires daily treatment, success depends on compliance.

If the vitamin D dose is administered in a single day, it is usually divided into 4 or 6 oral doses. An intramuscular injection is also available. Vitamin D (cholecalciferol) is well stored in the body and is gradually released over many weeks. Because both calcitriol and calcidiol have short half-lives, these agents are unsuitable for treatment, and they bypass the natural physiologic controls of vitamin D synthesis.

The single-day therapy avoids problems with compliance and may be helpful in differentiating nutritional rickets from familial hypophosphatemia rickets (FHR). In nutritional rickets, the phosphorus level rises in 96 hours and radiographic healing is visible in 6-7 days. Neither happens with FHR.

Orthopedic Consultation
If severe deformities have occurred, orthopedic correction may be required after healing. Most of the deformities correct with growth.