Osteomalacia in children; Vitamin D deficiency; Renal rickets
Rickets is a childhood disorder involving softening and weakening of the bones. It is primarily caused by lack of vitamin D, calcium, or phosphate.
Causes, incidence, and risk factors
Vitamin D may be absorbed from food by the intestines or may be produced by the skin when the skin is exposed to sunlight. In its active form, vitamin D acts as a hormone to regulate calcium absorption from the intestine and to regulate levels of calcium and phosphate in the bones.
Sunlight is important to skin production of vitamin D, and environmental conditions where sunlight exposure is limited may reduce this source of vitamin D. Lack of vitamin D production by the skin may occur if a person is confined indoors, or works indoors during the daylight hours, or lives in climates with little exposure to sunlight.
Because vitamin D is a fat-soluble vitamin, conditions that reduce digestion or absorption of fats will decrease the ability of vitamin D to be absorbed from the intestines.
When the body is deficient in vitamin D, it is unable to properly regulate calcium and phosphate levels. If the blood levels of these minerals become too low, other body hormones may stimulate release of calcium and phosphate from the bones to the bloodstream to elevate the blood levels.
Rickets is a bone disease that affects children when these deficiencies occur. It causes progressive softening and weakening of the bones’ structure. There is a loss of calcium and phosphate from the bones, which eventually causes destruction of the supportive matrix.
Rickets is fairly rare in the US. It is most likely to occur during periods of rapid growth, when the body demands high levels of calcium and phosphate. Rickets may be seen in young children 6 to 24 months old and is uncommon in newborns.
Nutritional causes of rickets occur because of a lack of vitamin D in the diet or in association with malabsorption disorders characterized by poor fat absorption.
A dietary lack of vitamin D may occasionally occur in people on a vegetarian diet who do not drink milk products or in people who are lactose intolerant (have trouble digesting milk products).
A dietary lack of calcium and phosphorous may also play a part in the nutritional causes of rickets. Rickets caused by a dietary lack of these minerals is rare in developed countries because calcium and phosphorous are present in milk and green vegetables.
Hereditary rickets is an inherited form of the disease caused when the kidneys are unable to retain phosphate. Rickets may also be caused by kidney disorders involving renal tubular acidosis.
Occasionally, it can also affect children who have disorders of the liver, do not adequately absorb fats and vitamin D, or cannot convert vitamin D to its active form.
Renal osteodystrophy occurs in people with chronic renal failure. The manifestation is virtually identical to that of rickets in children and that of osteomalacia or osteoporosis in adults.
- Bone pain or tenderness o Arms o Legs o Spine o Pelvis
- Skeletal deformities o Bowlegs o Forward projection of the breastbone (pigeon chest) o Bumps in the rib cage (rachitic rosary) o Asymmetrical or odd-shaped skull o Spine deformities (spine curves abnormally, including scoliosis or kyphosis) o Pelvic deformities
- Increased tendency toward bone fractures
- Dental deformities o Delayed formation of teeth o Defects in the structure of teeth, holes in the enamel o Increased incidence of cavities in the teeth (dental caries) o Progressive weakness o Decreased muscle tone (loss of muscle strength)
- Muscle cramps
- Impaired growth
- Short stature (adults less than 5 feet tall)
Signs and tests
A musculoskeletal examination reveals tenderness or pain of the bone itself, rather than in the joints or muscles.
- Calcium levels may be low. o Tetany (prolonged muscle spasm) may occur if serum levels of calcium are low. o Chvostek’s sign may be positive (a spasm of facial muscles occurs when the facial nerve is tapped) indicating low serum levels of calcium. o Serum calcium will confirm calcium levels.
- Serum phosphorus may be low.
- Serum alkaline phosphatase may be high.
- Arterial blood gases may reveal metabolic acidosis.
- Bone x-rays may show decalcification or changes in the shape or structure of the bones.
- A bone biopsy is rarely performed but will confirm rickets.
Other tests and procedures include the following:
- Urine calcium
- Calcium (ionized)
- ALP (alkaline phosphatase) isoenzyme
The treatment goals are to relieve symptoms and correct the cause of the condition. The underlying cause must be treated to prevent recurrence.
The replacement of deficient calcium, phosphorus, or vitamin D will eliminate most symptoms of rickets. Dietary sources of vitamin D include fish, liver, and processed milk. Exposure to moderate amounts of sunlight is encouraged. Treating rickets caused by metabolic abnormalities may require a special prescription for vitamin D.
Positioning or bracing may be used to reduce or prevent deformities. Some skeletal deformities may require corrective surgery.
The disorder may be corrected with replacement of deficient minerals and vitamin D. Laboratory values and x-rays usually improve after about 1 week, although some cases may be resistant and require large doses of minerals and vitamin D.
If rickets is not corrected while children are still growing, skeletal deformities and short stature may be permanent. If it is corrected while the child is young, skeletal deformities often diminish or disappear with time.
- Chronic skeletal pain
- Skeletal deformities
- Skeletal fractures, may occur without cause
Calling your health care provider
Call your child’s health care provider if you notice symptoms of rickets.
Rickets may be avoided by having your child maintain an adequate intake of calcium, phosphorus, and vitamin D. This may require dietary supplements in people who have gastrointestinal or other disorders - ask your child’s health care provider.
Renal (kidney) causes of vitamin D malabsorption should be treated promptly. Levels of calcium and phosphorus should be monitored regularly in people who have renal disorders.
Genetic counseling may help people with a family history of inherited disorders that can cause rickets.
by Armen E. Martirosyan, M.D.