Amyoplasia
Encyclopedia
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 sketetal 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 contractures.
Accounts for over 1/3 of the cases of arthrogryposis. Sporadic inheritance.
Characteristic appearance: Internally rotated shoulders, extended elbows, ulnar flexed wrists. More variable positioning of hips and knees. hips most often fixed and flexion and abduction. Half the hips are dislocated. Knees tend to be fixed in flexion. Equinovarus deformity of feet. most children have symmetrical limb involvement.
About 10% of children with amyoplasia have evidence of vascular compromise including bowel atresia
, abdominal wall defects
, gastroschisis
.
No single factor is found consistently in prenatal histories of patients with amyoplasia.
(AMC). AMC is a term used to describe a condition where multiple joint contractures are present at birth. Arthrogryposis is derived from the Greek word meaning "with crooking of joints," and AMC can be translated to mean "curved joints, multiple, evident at It occurs in about one out of every 3,000 live births. There are more than 150 types of AMC. Amyoplasia accounts for 40% of AMC cases.
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.
The fetal akinesia in amyoplasia is thought to be caused by various maternal and fetal abnormalities. In some cases, the mother's uterus does not allow for adequate fetal movement because of a lack of amniotic fluid, known as oligohydramnios
, or an abnormal shape to the uterus, called a bicornuate uterus
.
There may also be a myogenic
cause to the fetal akinesia, 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 the fetal akinesia and be the primary cause of amyoplasia. Additionally, malformations may occur in the central nervous system 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 fetal akinesia may include a maternal fever during pregnancy or a virus.
, OT and multiple orthopedic procedures. Initial passive stretching to improve joint mobility. Most children require therapy for years. Almost 2/3 end up with ambulation. The older the child, the more likely the independent ambulation with or without braces or assistance. The majority of children in school are in regular classes. Most read and write comparable to peers.
Arthrogryposis
Arthrogryposis, also known as Arthrogryposis Multiplex Congenita, is a rare congenital disorder that is characterized by multiple joint contractures and can include muscle weakness and fibrosis. It is a non-progressive disease...
.
It is characterized by quadrimelic involvement and replacement of sketetal 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 contractures.
Accounts for over 1/3 of the cases of arthrogryposis. Sporadic inheritance.
Characteristic appearance: Internally rotated shoulders, extended elbows, ulnar flexed wrists. More variable positioning of hips and knees. hips most often fixed and flexion and abduction. Half the hips are dislocated. Knees tend to be fixed in flexion. Equinovarus deformity of feet. most children have symmetrical limb involvement.
About 10% of children with amyoplasia have evidence of vascular compromise including bowel atresia
Intestinal atresia
Intestinal atresia is a malformation where there is a narrowing or absence of a portion of the intestine. This defect can either occur in the small or large intestine.-Types of intestinal atresia:...
, abdominal wall defects
Abdominal wall defect
An infant born with an abdominal wall defect has an abnormal opening on the abdomen. This often causes the intestines and other organs to form outside of the body.There are two main types of abdominal wall defects - omphalocele and gastroschisis....
, gastroschisis
Gastroschisis
Gastroschisis represents a congenital defect characterized by a defect in the anterior abdominal wall through which the abdominal contents freely protrude. There is no overlying sac and the size of the defect is usually less than 4 cm...
.
No single factor is found consistently in prenatal histories of patients with amyoplasia.
Diagnosis
It is the most common form of arthrogryposis multiplex congenitalArthrogryposis
Arthrogryposis, also known as Arthrogryposis Multiplex Congenita, is a rare congenital disorder that is characterized by multiple joint contractures and can include muscle weakness and fibrosis. It is a non-progressive disease...
(AMC). AMC is a term used to describe a condition where multiple joint contractures are present at birth. Arthrogryposis is derived from the Greek word meaning "with crooking of joints," and AMC can be translated to mean "curved joints, multiple, evident at It occurs in about one out of every 3,000 live births. There are more than 150 types of AMC. Amyoplasia accounts for 40% of AMC cases.
Causes
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.
The fetal akinesia in amyoplasia is thought to be caused by various maternal and fetal abnormalities. In some cases, the mother's uterus does not allow for adequate fetal movement because of a lack of amniotic fluid, known as oligohydramnios
Oligohydramnios
Oligohydramnios is a condition in pregnancy characterized by a deficiency of amniotic fluid. It is the opposite of polyhydramnios.-Diagnosis:Diagnosis is made by ultrasound measurement of the amniotic fluid index...
, or an abnormal shape to the uterus, called a bicornuate uterus
Bicornuate uterus
A bicornuate uterus or bicornate uterus, commonly referred to as a "heart-shaped" uterus, is a type of uterine malformation where two "horns" form at the upper part of the uterus.-Pathophysiology:A bicornuate uterus is formed during embryogenesis....
.
There may also be a myogenic
Myogenic
Myogenic contraction refers to a contraction initiated by the myocyte cell itself instead of an outside occurrence or stimulus such as nerve innervation.- Unstable Membrane Potentials :...
cause to the fetal akinesia, 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 the fetal akinesia and be the primary cause of amyoplasia. Additionally, malformations may occur in the central nervous system 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 fetal akinesia may include a maternal fever during pregnancy or a virus.
Symptoms
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 (also known as fetal akinesia) 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.Treatment
Surgery may be necessary to address the congenital deformities frequently occurring in conjunction with arthrogryposis. Surgery on feet, knees, hips, elbows and wrists may also be useful if more range of motion is needed after therapy has achieved maximum results. In some cases, tendon transfers can improve function. Congenital deformities of the feet, hips and spine may require surgical correction at or about one year of age.Prognosis
Overall prognosis for these children with amyoplasia is good. Intensive therapies throughout developing years include PT, OT and multiple orthopedic procedures. Initial passive stretching to improve joint mobility. Most children require therapy for years. Almost 2/3 end up with ambulation. The older the child, the more likely the independent ambulation with or without braces or assistance. The majority of children in school are in regular classes. Most read and write comparable to peers.