Description, Causes and Risk Factors:
Deficient formation of muscle tissue and deficient muscle growth.
Amyoplasia is a generalized lack in the newborn of muscular development and growth, with contracture and deformity at most joints. It is the most common form of arthrogryposis.
It is characterized by quadrimelic involvement and replacement of skeletal muscle by dense fibrous tissue and fat. Studies involving amyoplasia have revealed similar findings of the muscle tissue due to various causes including that seen in sacral agenesis and diseases of the anterior horn cell. So amyoplasia may not describe just one group of patients but may be an intermediate common pathway rather than the primary cause of the contractors.
There is no single factor that is consistently found in the prenatal history of individuals affected with amyoplasia and, in some cases, there is no known cause of the disorder.
Amyoplasia is a sporadic condition that occurs due to lack of fetal movement in the womb. There is no specific gene that is known to cause the disorder. It is thought to be multifactorial, meaning that numerous genes and environmental factors play a role in its development. The recurrence risk is minimal for siblings or children of affected individuals. There have been no reports of recurrent cases of amyoplasia in a family.
There may also be a myogenic cause to the amyoplasia, meaning that fetal muscles do not develop properly due to a muscle disease (for example, a congenital muscular dystrophy). Similarly, connective tissue tendon and skeletal defects may contribute to cause of amyoplasia. Additionally, malformations may occur in the central nervous system (CNS) and/or spinal cord that can lead to a lack of fetal movement in utero. This neurogenic cause is often accompanied by a wide range of other conditions. Other causes of amyoplasia may include a maternal fever during pregnancy or a virus.
Overall prognosis for these children with amyoplasia is good. Intensive therapies throughout developing years include physical therapy, occupational therapy and multiple orthopedic procedures. Most children require therapy for years, but almost 2/3 are eventually able to walk, with or without braces, and attend school. Most read and write at a level comparable to their peers.
Amyoplasia results when a fetus is unable to move sufficiently in the womb. Mothers of children with the disorder often report that their baby was abnormally still during the pregnancy. The lack of movement in utero allows extra connective tissue to form around the joints and, therefore, the joints become fixed. This extra connective tissue replaces muscle tissue, leading to weakness and giving a wasting appearance to the muscles. Additionally, due to the lack of fetal movement, the tendons that connect the muscles to bone are not able to stretch to their normal length and this contributes to the lack of joint mobility as well.
There are no tests available to definitively diagnose amyoplasia prior to or after birth. The condition may be suspected prenatally if limb deformities are seen on ultrasound (i.e., clubfoot) or if decreased fetal movement is noted. Generally, the diagnosis of amyoplasia is made by ruling out other disorders that cause joint contractures. This is often done via muscle biopsies, blood tests, computed tomography (CT) scans, chromosomal studies, and clinical findings.
Treatment and management of amyoplasia should involve a multidisciplinary team of health care providers, including pediatrics, neurology, orthopedic surgery, genetics, physical therapy, and occupational therapy. The main goal of treatment is to improve function, not to improve cosmetic appearance.
Generally, it is important to focus on the elbow and wrist in the upper extremity, as contractures in these joints are more problematic than those in the shoulder. Particular attention should be paid to the upper extremity. Due to the emphasis that parents place on encouraging their child to walk, the importance of the function of the arms is often overlooked. For the lower extremity, it is important to pay attention to all joints, however, it is recommended that deformities of the feet are treated first, followed by the knees and then the hips.
Most often, intervention begins immediately after birth with physical therapy and range of motion exercises designed to improve flexibility in muscles and joints. Once the joint is positioned adequately by these exercises, splinting is used to maintain the gains in range of motion. If the joint cannot be positioned adequately with range of motion exercises, casting or soft-tissue release surgery with subsequent casting may be necessary.
In addition to physical therapy, surgery is often necessary for patients with amyoplasia. Muscle transfer is a surgical procedure that involves moving muscles from one location in the body to another location where they might perform better. This is an option for affected patients. However, if muscles are nonfunctional or limited in function as they often are in amyoplasia, this procedure may not be effective. Osteotomy is the surgical cutting of a portion of the bone to correct deformity and may be necessary in some cases of amyoplasia. However, due to the possibility of the recurrence of a bone deformity, this procedure should be postponed until an individual has reached skeletal maturity. Other surgery may be necessary to correct clubfeet, scoliosis, or joint dislocations. Additionally, hernias and other conditions associated with amyoplasia may require surgical intervention.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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