Bone density disorders in children affect the density and strength of bones and cause bones to break easily and grow abnormally.
These disorders occur when the body does not recycle old bone cells.
Typical symptoms include impaired bone growth and bones that easily break.
The diagnosis is based on symptoms and x-rays and sometimes blood tests.
Medications and surgery can help relieve some of problems caused by the disorders.
Bone density is a measurement of minerals in bone tissue. Bones that are too dense or that are not dense enough are prone to breaking (fracture).
Some bone density disorders result from abnormalities in certain genes. These abnormal genes are hereditary. That is, they may be passed down from parent to child. Others result from poor nutrition, hormone problems, or other medical disorders.
Bone density disorders are classified into those that cause low or high bone density.
(See also Overview of Bone Disorders in Children.)
Low Bone Density Disorders in Children
Bone tissue in children undergoes a continuous cycle of formation and resorption to support growth and skeletal development. In children with a low bone density disorder, this balance is disrupted by a specific cause or by immobility, resulting in reduced bone mass and impaired bone structure. Consequently, bones become thinner, weaker, and more susceptible to fractures, including in the spine and the long bones (such as the arm and leg bones). The combination of these factors can affect normal growth, movement, and overall development in children.
The main low bone density disorders in children are osteogenesis imperfecta, osteoporosis, and rickets.
Low bone density in children can have various causes, such as poor nutrition, low level of vitamin D, gene mutations, low levels of several hormones (such as growth hormone, estrogen, and testosterone), medical conditions (such as celiac disease and chronic kidney disease), and medications (such as steroids [sometimes called glucocorticoids or corticosteroids]).
To determine whether a child has low bone density, doctors do a dual-energy x-ray absorptiometry (DXA) scan. The DXA scan takes high-energy and low-energy x-rays of the spine and hip, which are the sites at which major fractures are likely to occur. The difference between the high- and low-energy x-ray readings allows doctors to calculate bone density. The result is reported as a Z-score, which compares the child's bone density to the bone density of a healthy child of the same sex, age, and body size. The lower the bone density, the lower the Z-score. A Z-score of –2.0 or lower indicates low bone density.
Doctors often treat the underlying cause of the disorder. Lifestyle changes and, in some cases, medications may also be helpful.
High Bone Density Disorders in Children (Osteopetroses)
High bone density disorders are called osteopetroses. Osteopetroses are rare, inherited disorders that are caused by abnormalities in certain genes.
Bone cells constantly but slowly form, live for a period, and then are reabsorbed in a recycling process. In osteopetrosis, the body does not recycle old bone cells. The result is increased density or thickness of the bones and changes in how the bones are shaped. Although the bones are denser, the increased thickness and changes in the internal structure and shape make the bones weak, brittle, and fragile. The dense bone tissue also crowds out the bone marrow, which is where blood cells are formed. The spleen may be overactive and lead to an increased breakdown of red blood cells.
Osteopetroses range from mild to severe and can even be life threatening. Symptoms of osteopetroses may begin in infancy (early onset) or later in life (delayed onset).
Symptoms of Osteopetroses
Although osteopetroses comprise a range of different disorders, many of the same symptoms develop in most of them. Bone growth is usually impaired. Bones thicken and break easily. Formation of blood cells may be impaired because there is less bone marrow, leading to infection or bleeding. Bleeding usually occurs after minor accidents or injuries (for example, nose picking leads to nosebleeds, and gums bleed after brushing teeth).
An overgrowth of bone in the skull can cause pressure in the skull to increase; compress nerves, causing facial paralysis or loss of vision or hearing; and can distort the face and teeth. The bones in the fingers and feet, the long bones of the arms and legs, the spine, and the pelvis may be affected.
Diagnosis of Osteopetroses
X-rays
Blood tests
Genetic tests
Doctors usually base the diagnosis of osteopetroses on symptoms and x-rays that show very dense or malformed bones.
When the person has no symptoms, osteopetrosis is sometimes detected only by chance, after a doctor sees very dense bones on x-rays taken for an unrelated purpose.
If doctors suspect a person has osteopetrosis, they may do blood tests. Blood tests may show whether the person has reduced numbers of red blood cells (anemia) or a low number of platelets (thrombocytopenia).
Doctors also perform genetic testing to confirm the diagnosis by identifying specific abnormalities that affect how bone cells function.
Treatment of Osteopetroses
Steroids (also called glucocorticoids or corticosteroids)
Sometimes stem cell transplantation
Sometimes surgery
Steroids, such as prednisone, decrease the formation of new bone cells and may increase the rate of removal of old bone cells, strengthening bones. Steroids may also help relieve bone pain and improve muscle strength. Steroids, such as prednisone, decrease the formation of new bone cells and may increase the rate of removal of old bone cells, strengthening bones. Steroids may also help relieve bone pain and improve muscle strength.
Stem cell transplantation may cure some infants with early-onset osteopetrosis, but it may not correct pre-existing defects in kidney function.
If nerves going through the skull are compressed, surgery may be required to take pressure off the nerves. Surgery may also be needed to relieve increased pressure in the skull. Plastic surgery may be done to correct severe deformities of the face and jaw.
Orthodontic treatment may be needed to correct distorted teeth.
Most minor fractures are treated with a cast or a traction device. Major fractures (for example, broken bones are separated or immobilizing) may be need to be treated surgically. Anemia and low platelets (causing bleeding) are typically treated with blood transfusions. In rare cases where the spleen is overactive, removing the spleen may help with both anemia and low platelets.
Infections are treated with antibiotics.
Prognosis for Osteopetroses
Early-onset osteopetrosis that is not treated with stem cell transplantation is usually fatal during infancy or early childhood. Death usually results from anemia, infection, or bleeding.
Late-onset osteopetrosis is often mild.
