Spina bifida
From Wikipedia, the free encyclopedia
| ICD-10 | Q05., Q76.0 | |
|---|---|---|
| ICD-9 | 741, 756.17 | |
| OMIM | 182940 | |
| DiseasesDB | 12306 | |
| eMedicine | orthoped/557 | |
| MeSH | C10.500.680.800 | |
Spina bifida (Latin: "split spine") is a developmental birth defect involving the neural tube: incomplete closure of the embryonic neural tube results in an incompletely formed spinal cord. In addition, the bones of the spine ([vertebrae]) overlying the open portion of the spinal cord do not fully form and remain unfused and open. This allows the abnormal portion of the spinal cord to protrude through the opening in the bones. There may or may not be a fluid filled sac surrounding the open spinal cord. Other neural tube defects include anencephaly, a condition in which the portion of the neural tube which will become the cerebrum ([front of the brain])brain does not close and encephalocele which results when other parts of the brain remain unfused.
Spina bifida malformations fall into three categories: spina bifida occulta, spina bifida cystica (myelomeningocele), and meningocele. The most common location of the malformations is the lumbar and sacral areas of the spinal cord. Meningomyelocele is the most significant form and that which leads to disability in most affected individuals. The terms spina bifida and meningomyelocele are usually used interchangably.
Spina bifida can be surgically closed after birth, but this does not restore normal function to the affected part of the spinal cord and an individuals with this condition will have dysfunction of the spinal cord and associated nerves from the point of the open defect and below. Intrauterine surgery for spina bifida has also been performed and the safety and efficacy of this procedure is currently being investigated with an NICHD-funded ([National Institute of Child Health and Human Development)] grant . The incidence of spina bifida can be decreased up to 70% when daily folic acid supplements are taken for three months prior to the pregnancy.
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[edit] Incidence
Spina bifida is one of the most common birth defects, with an average worldwide incidence of 1-2 cases per 1000 births, but certain populations have a significantly greater risk. In the United States, the average incidence of 0.7 per 1000 live births. The incidence is higher on the East Coast than on the West Coast, and higher in whites (1 case per 1000 live births) than in African Americans (0.1-0.4 case per 1000 live births). Immigrants from Ireland have a higher incidence of spina bifida than do nonimmigrants.[1][2]
The highest incidence rates worldwide are found in parts of the British Isles, mainly Ireland and Wales, where 3-4 cases of myelomeningocele per 1000 population have been reported, along with more than 6 cases of anencephaly (both live births and stillbirths) per 1000 population. The reported overall incidence of myelomeningocele in the British Isles is 2-3.5 cases per 1000 births.[3][4]
Siblings of patients with spina bifida have an increased incidence of neural tube defects.[5][6]
[edit] Clinical presentation
[edit] Spina bifida occulta
Occulta is Latin for "hidden." This is one of the "mildest" forms of spina bifida although the degree of disability can vary depending upon the location of the lesion and actually be very severe in some patients.
In occulta there is no opening of the back, but the outer part of some of the vertebrae are not completely closed. The split in the vertebrae is so small that the spinal cord does not protrude. The skin at the site of the lesion may be normal, or it may have some hair growing from it; there may be a dimple in the skin, or a birthmark. People with this form may have incontinence, ambulatory problems, loss of sensation, deformities of the hips, knees or feet and loss of muscle tone. Depending on the location of the lesion, intense pain may occur originating in the lower back, and continuing down the leg to the back of the knee. Other related problems that may occur include Chiari malformation, most likely type I; scoliosis; and tethered cord. Many people with the mildest form of this type of spina bifida do not even know they have it, or symptoms do not appear until later in life often presenting as uncontrolable case of incontience.
[edit] Spina bifida cystica (myelomeningocele)
In this, the most serious form, the unfused portion of the spinal cord protrudes through an opening in the overlying vertebrae. The meningeal membranes that cover the spinal cord may or may not form a sac enclosing the spinal elements. Superficially, the cyst may resemble an unrelated defect, sacrococcygeal teratoma. The unfused elements of the spinal cord can be surgically closed along with the overlying muscle and skin shortly after birth (see below).
The incompletely closed portion of the spinal cord and the nerves which originate at that level of the cord are damaged or not properly developed. As a result, there is usually some degree of paralysis and loss of sensation below the level of the spinal cord defect. Thus, the higher the level of the defect the more severe the associated nerve dysfunction and resultant paralysis. Most children and adults with this condition experience problems with bowel and bladder control since the nerves which control these functions originate at the lowest part of the spinal cord. Virtually all individuals with spina bifida will have an associated abnormality of the back of the brain, or cerebellum, called the Arnold Chiari II malformation. In affected individuals the back portion of the brain is displaced from the back of the skull down into the upper neck. In approximately 90% of the people with myelomeningocele, hydrocephalus—extra fluid in the ventricles of the brain—will also occur because the displaced cerebellum interferes with the normal flow of cerebro-spinal fluid. The myelomeningocele (or perhaps the scarring due to surgery) tethers the spinal cord to the enveloping vertebra. In some individuals this causes significant traction on the spinal cord and can lead to a worsening of the paralysis, curvature of the spine, also known as scoliosis, back pain, or worsening bowel and/or bladder function.
[edit] Meningocele
In this, the least common form, the outer part of some of the vertebrae are split and the meninges are damaged and pushed out through the opening, appearing as a sac or cyst, which contains both the meninges and cerebrospinal fluid. The spinal cord and nerves are not involved and neurologic function is normal. There are usually no negative long-term effects, although problems such as tethered cord have been known to arise.
[edit] Sequelae
The most common location of the malformations is the lumbar and sacral areas of the spinal cord. The lumbar nerves control the muscles in the hip, leg, knee and foot, and help to keep the body erect. The sacral nerves control some of the muscles in the feet, bowel and urinary bladder, and the ability to have an erection. Some degree of impairment can be expected in these areas, resulting in varying degrees of paralysis, scoliosisabsence of skin sensation, and poor or absent bowel and/or bladder control, curveture of the spine ([scoliosis]), depending on the severity and location of the lesion damage on the spine. Although these individuals are rarely mentally retarded, in most cases there are cognitive problems.
Tethered Spinal Cord syndrome, with symptoms such as lower body pain, leg weakness, incontinence, curveture of the spine scoliosis, numbness, is a common problem associated with spina bifida. Indeed 100% of spina bifida myelomeningocele patients have Tethered Cord on imaging studies such as Magnetic Resonance Imaging/MRI, but not all will develop symptoms. A tethered cord is thought to result from scar tissue which forms following the initial surgery to close the open defect. Symptoms caused by a tethered cord are rare in infancy and early childhood. Once symptoms develop it is important to make the diagnosis early, before permanant damage is done to the spinal cord and nerves.
According to the Spina Bifida Association of America (SBAA), over 73% of people with spina bifida develop an allergy to latex, ranging from mild to life-threatening. The common use of latex in medical facilities makes this a particularly serious concern. The most common approach is to try and avoid development of the allergy by avoiding contact with latex containing products such as examination gloves, catheters tubes used in the managementn of bladder dysfunction, and many of the products used by dentists.
[edit] Pathophysiology
Spina bifida is caused by the failure of the neural tube to close during the first month of embryonic development (often before the mother knows she is pregnant).
Normally the closure of the neural tube occurs around the twenty-eighth day after fertilization. However, if something interferes and the tube fails to close properly, a neural tube defect will occur. Medications such as some anticonvulscents, diabetes, having a relative with spina bifida, obesity, and an increased body temperature from fever or external sources such as hot tubs and electric blankets can increase the chances a woman will conceive a baby with a spina bifida.
Research has shown that lack of folic acid (folate) is a contributing factor in the pathogenesis of neural tube defects, including spina bifida. Supplementation of the mother's diet with folate can reduce the incidence of neural tube defects by about 70%, and can also decrease the severity of these defects when they occur.[7][8][9] As yet it is unknown how or why folic acid has this effect.
Spina bifida does not follow direct patterns of heredity like muscular dystrophy or haemophilia. Studies show that a woman who has had one child with a neural tube defects such as spina bifida, have about a 3% risk to have another child with a neural tube defect. This risk can be reduced to about 1% if the woman takes high doses (4 mg/day) of folic acid before and during pregnancy.
[edit] Treatment
There is no cure for nerve damage due to spina bifida. To prevent further damage of the nervous tissue and to prevent infection pediatric neurosurgeons operate to close the opening on the back. During the operation, the spinal cord and its nerve roots are put back inside the spine and covered with ([meninges)], muscle and skin. In addition, a shunt may be surgically installed to provide a continuous drain for the cerebrospinal fluid produced in the brain. Shunts most commonly drain into the abdomen.
Most individuals with myelomeningocele will need periodic evaluations by specialists including orthopedists to check on their bones and muscles, neurosurgeons to evaluate the brain and spinal cord and urologists for the kidneys and bladder. Such care is best begun immediately after birth. Most affected individuals will require braces, crutches, walkers or wheelchairs to maximize their mobility. The higher the level of the spina bifida defect the more severe the paralysis. Thus, those with low levels may need only short leg braces while those with higher levels do best with a wheelchair. Many will need to manage their urinary system with a program of catheterization. They will need to insert a tube into their bladders to drain urine every 4-6 hours during the day and may need medications to improve their dryness. Most will also require some sort of bowel management program.
[edit] Clinical trial
Management of Myelomeningocele Study (MOMS)[10] is a phase III clinical trial to evaluate the safety and efficacy of fetal surgery to close a myelomeningocele. This involves surgically opening the pregnant mother's abdomen and uterus to operate on the fetus. Fetal skin grafts are used to cover the exposed spinal cord, to protect it from further damage caused by prolonged exposure to amniotic fluid. The fetal surgery may decrease some of the damaging effects of the spina bifida.
Pregnant women who consent to participate and meet all eligibility criteria are referred to one of three centers in the United States, located in California, Tennessee, and Pennsylvania. The centers provide final evaluation, randomization, surgery and follow-up assessments. Participants' travel, lodging, relevant medical and surgical procedures, and related costs are covered by the clinical trial, not by the participants' medical insurance.
Major Eligibility Criteria:
- Gestational age at randomization: 19 – 25 weeks
- Myelomeningocele defect must start at: T1-S1 (may extend below S1)
- Fetal hindbrain herniation (Arnold-Chiari malformation type II)
- Maternal Body Mass Index < 35
- United States resident
[edit] Prevention
There is no single cause of spina bifida or any known way to prevent it entirely. However, dietary supplementation with folic acid (folate) has been shown to be helpful in preventing spina bifida (see above). Sources of folic acid include: whole grains, fortified breakfast cereals, dried beans, leaf vegetables and fruits.[11]
Folate fortification of enriched grain products has been mandatory in the United States since 1998. The FDA and UK recommended amount of folic acid for women of childbearing age and women planning to become pregnant is at least 0.4 mg/day of folic acid from at least three months before conception, and continued for the first 12 weeks of pregnancy.[12] Women who have already had a baby with spina bifida or other type of neural tube defect, or are taking anticonvulsant medication should take a higher dose of 4–5 mg/day.[12]
[edit] Additional information
Spina bifida is a type of neural tube defect. Neural tube defects can usually be detected during pregnancy by testing the mother's blood AFP screening or a detailed fetal ultrasound. Spina bifida may be associated with other malformations as in dysmorphic syndromes, often resulting in spontaneous miscarriage. However, in the majority of cases spina bifida is an isolated malformation. Spina bifida has varying prevalence in different human populations. This and extensive evidence from mouse strains with spina bifida suggests a genetic basis. As with other human diseases such as cancer, hypertension and atherosclerosis (coronary artery disease), spina bifida likely results from the interaction of multiple genes and environmental factors. Despite much research, it is still unknown what causes the majority of cases. Nevertheless, there is substantial evidence supporting a significant protective effect of folic acid (0.4 mg per day) when taken by women early in pregnancy. It is important to note that spina bifida occurs by the fourth week of pregnancy before many women will be aware of a pregnancy, thus it is generally recommended that women of child-bearing age take a folic acid supplement (most multivitamins contain 0.4 mg folic acid) if they are sexually active. Genetic counseling and further genetic testing, such as amniocentesis, may be offered during the pregnancy as some neural tube defects are associated with genetic disorders such as trisomy 18.
[edit] People
People of note born with spina bifida:
- Jean Driscoll[1], Olympian and eight-time Boston Marathon winner
- Tanni Grey-Thompson, Welsh Paralympian
- Lawrence Gwozdz, U.S. saxophonist
- Blaine Harrison, of the British band Mystery Jets
- Rene Kirby, U.S. actor, starred in Shallow Hal, 2001 [13]
- John Mellencamp, U.S. rock and roll musician
- Bobby Steele, U.S. punk rock guitarist and songwriter
- Jeffrey Tate, British conductor
- Hank Williams, U.S. country music singer
- Justin Yoder, American soap box racer
- Mighty Mike McGee, American 2006 World Slam Poetry Champion
- David Yip, Canadian Sex Offender
[edit] Footnotes
- ^ Lemire RJ (1988). Neural tube defects. JAMA 259(4): 558-62.
- ^ Cotton P (1993). Finding neural tube 'zippers' may let geneticists tailor prevention of defects. JAMA 270(14): 1663-4.
- ^ Lemire RJ (1988). Neural tube defects. JAMA 259(4): 558-62.
- ^ Cotton P (1993). Finding neural tube 'zippers' may let geneticists tailor prevention of defects. JAMA 270(14): 1663-4.
- ^ Lemire RJ (1988). Neural tube defects. JAMA 259(4): 558-62.
- ^ Cotton P (1993). Finding neural tube 'zippers' may let geneticists tailor prevention of defects. JAMA 270(14): 1663-4.
- ^ Holmes LB (1988). Does taking vitamins at the time of conception prevent neural tube defects? JAMA 260(21): 3181
- ^ Milunsky A, Jick H, Jick SS, et al. (1989). Multivitamin/folic acid supplementation in early pregnancy reduces the prevalence of neural tube defects. JAMA 262(20): 2847-52.
- ^ Mulinare J, Cordero JF, Erickson JD, et al. (1988). Periconceptional use of multivitamins and the occurrence of neural tube defects. JAMA 260(21): 3141-5.
- ^ MOMS websiteMOMS blurb on About.comMOMS summary on ClinicalTrials.gov
- ^ Folic Acid Fortification. FDA (February 1996).
- ^ a b Why do I need folic acid?. NHS Direct (27/04/2006). Retrieved on August 19, 2006.
- ^ http://movies.about.com/library/weekly/aa110201g.htm
[edit] See also
- Hydrocephalus
- Valproic acid
- Neural tube defects
- Open fetal surgery
- Pseudomeningocele
- Samuel Armas (an early recipient of open fetal surgery)
[edit] External links
- CDC’s National Center on Birth Defects and Developmental Disabilities
- the International Federation for Spina Bifida and Hydrocephalus (IF) - the umbrella organisation for national spina bifida and hydrocephalus organisations
- Personal Accounts of Spina Bifida Patients
- Association for Spina Bifida and Hydrocephalus
- National Spina Bifida Association
- The Management of Myelomeningocele Study (MOMS)
