Skeletal dysplasias
Overview
Skeletal dysplasias are a group of congenital abnormalities of the bone and cartilage that are characterized by short stature. Skeletal dysplasia, sometimes called dwarfism, is a disorder of short stature defined as height that is three or more standard deviations below the mean height for age, race, and gender. Although all skeletal dysplasias involve disproportionately short stature, there are many other associated conditions. Skeletal dysplasia may also have additional skeletal abnormalities, including: * short arms and truck, bowlegs, and a waddling gait * skull malformations, such as a large head, cloverleaf skull, craniosynostosis (premature fusion of the bones in the skull), and wormian bones (abnormal thread-like connections between the skull bone) * anomalies of the hands and feet, including polydactyly (extra fingers), "hitchhiker" thumbs, and abnormal finger and toe nails * chest anomalies, such as pear-shaped chest and narrow thorax Other anomalies that may be present in individuals with skeletal dysplasia include: * anomalies of the eyes, mouth, and ears, such as congenital cataract, myopia (nearsightedness), cleft palate, and deafness * brain malformations, such as hydrocephaly, porencephaly, hydranencephaly, and agenesis of the corpus callosum * heart defects, such as atrial septal defect (ASD), patent ductus arteriosus (PDA), and transposition of the great vessels (TGV) * developmental delays and mental retardation
Symptoms
The primary sign of skeletal dysplasia is abnormally shortened long bones in the legs and arms, short trunk, and abnormalities of the skull. In addition to the skeletal system, skeletal dysplasia disorders may also affect the heart, the face, extremities, and joints. Some forms are lethal, and a significant number of fetuses with skeletal dysplasia die in utero.
Diagnosis
Many skeletal dysplasias can be diagnosed prenatally during routine prenatal ultrasound. If skeletal dysplasia is suspected, assessment and careful measurement of the extremities, thorax, spine, and facial structure can detect signs of the condition. Fetal movement may be decreased, and associated congenital heart and renal heart defects may be observed as well. After birth, x rays are the most effective diagnostic tool for evaluating the skeleton. A skeletal study includes views of the long bone, hands and feet, skull, chest, spine, and pelvis. Abnormal x-ray results that may indicate a skeletal dysplasia include: * dumbbell-shaped long bones * bowing of the arms and legs * oval-shaped translucencies in the femur and humerus * scapula hypoplasia (small shoulder blades) * abnormal pelvis * vertebral abnormalities * rib abnormalities, including cupping of the ends or shortening of the entire rib and stippled or spotted appearance to the cartilage * epiphyses (growth centers of the long bones) abnormalities, including cone shape, stippled appearance, or an absence of calcification centers * long bone fractures Computed tomography (CT) scan and magnetic resonance imaging (MRI) are useful in assessing concurrent brain anomalies. MRI is useful in determining the extent and type of spinal abnormalities and compression present. Three-dimension CT scan is used to evaluate craniofacial anomalies prior to reconstructive surgery. MRI of the spine is also helpful in pre-surgical planning prior to surgical treatment of spinal and pelvic abnormalities. Chromosome analysis may be performed to help determine the type of skeletal dysplasia an individual has. This is important so that other associated conditions can be diagnosed and treated as well. Other diagnostic procedures that may be performed, including molecular analysis to identify single gene mutations, sleep studies to evaluate potentially life-threatening sleep apnea that is often a problem for individuals with skeletal dysplasia, histological studies to examine specific types of cells that identify some skeletal dysplasia forms, and an echocardiogram (ECHO) to evaluate the heart for defects.
Prognosis
While some skeletal dysplasias are lethal, most individuals with skeletal dysplasia have a normal life expectancy. The associated conditions may require medical and surgical treatment; however, these treatments are highly effective. Intelligence is usually normal. Most people with skeletal dysplasia have an excellent prognosis.
Treatment
Treatment and management of children with skeletal dysplasia begins, in some cases, at birth. Neonatal resuscitation may be necessary for infant with certain more severe types of skeletal dysplasia in which the thoracic cavity is extremely small. This intervention can be life-saving. The medical management of children with skeletal dysplasia begins at birth and continues into adulthood. Careful monitoring of height, weight, and head circumference is essential. Obesity is a risk for those with skeletal dysplasia. Excess weight can cause serious complications, including breathing difficulties such as sleep apnea, and may aggravate other spinal cord compression and joint instability found in many types of skeletal dysplasia. Surgical treatment of skeletal dysplasia varies depending on the specific type present and the associated conditions. Sleep apnea may be treated by removal of the adenoids. Spinal abnormalities, such as spinal cord compression, scoliosis, kyphosis, and lordosis, may be treated surgically. A spinal column fusion can relieve the stress on the spinal cord caused by malformations of the spinal column. In a spinal fusion, two or more vertebrae are fused together using bone grafts or metal rods. In some individuals with short-limbed types of skeletal dysplasia, bone growth may be induced by a surgical bone-lengthening procedure. This procedure involves several surgeries and an extensive recovery period. The bone to be lengthened is cut. Leaving a narrow gap between the two pieces of bone, metal pins are inserted into the bone and the skin is closed. An external frame is attached to the pins and, gradually, the bone is pulled apart just enough to provide a small gap for the bone to grow into. As the bone grows, the space is widened and more bone grows. After the bone has healed, the pins are surgically removed. In some cases, as much as 6 in (15 cm) has been added to leg length using this procedure.