Developmental Disabilities
Roberta E. Bauer
Mark H. Deis
The developmental disabilities reviewed in this chapter include:
Mental retardation (MR)
Cerebral palsy (CP)
Myelomeningocele (MMC)
Autism and pervasive developmental disorder
Attention deficit hyperactivity disorder (ADHD)
Fetal alcohol syndrome
Learning disabilities/educational issues
Language/speech delay
MENTAL RETARDATION
The features of MR are summarized in Table 39.1.
Etiology and Epidemiology
Standardized measures of intelligence assume that intelligence occurs along a Gaussian (bell-shaped) distribution curve. MR is defined as an intelligence quotient (IQ) that is more than two standard deviations below the mean for that age (i.e., an IQ of 70 seen in 3% of the population)
on a standardized IQ test. The diagnosis of MR requires poor performance both on standardized tests of intelligence and in daily adaptive behavior (must be significantly limited in adaptive functioning in at least two of the following: communication, self-care, social skills, self-direction, academic skills, work, leisure activities, health, and safety). Because of the requirement that affected individuals must meet both criteria, the overall prevalence of MR is 1% to 2%.
on a standardized IQ test. The diagnosis of MR requires poor performance both on standardized tests of intelligence and in daily adaptive behavior (must be significantly limited in adaptive functioning in at least two of the following: communication, self-care, social skills, self-direction, academic skills, work, leisure activities, health, and safety). Because of the requirement that affected individuals must meet both criteria, the overall prevalence of MR is 1% to 2%.
TABLE 39.1 SUMMARY OF MENTAL RETARDATION | |||||||||||||||||||||||||||||||||
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Several classification schema exist, but classification according to IQ scores is most often defined as:
70 to 85, borderline normal intelligence
50 to 70, mild MR
35 to 50, moderate MR
20 to 35, severe MR
<20, profound MR
This classification scheme is slowly being replaced by a scheme on the basis of “Intensity of Needed Levels of Support” required by the child: intermittent, limited, extensive, or pervasive.
Intelligence is remarkably stable over time, so that an individual with an IQ of 60 can be expected to acquire new skills at a rate 60% of that of an individual with average intelligence. Common causes of MR may be:
Metabolic
Lysosomal storage disease (includes the mucopolysaccharidoses, mucolipidoses, and oligosaccharidoses; organic acidemias and aminoacidemias)
Leukodystrophies
Any postnatal condition that can cause hyperbilirubinemia, hypoglycemia, or hypernatremia
Chromosomal
Trisomies (13, 18, 21)
Fragile X syndrome
X-linked disorders
Translocations and deletions
Infectious
Congenital TORCH (toxoplasmosis, rubella, cytomegalovirus, herpes simplex) infection
Perinatally acquired human immunodeficiency virus infection
Postnatally acquired meningitis and encephalitis
Teratogenic
Alcohol, drugs, radiation, maternal phenylketonuria, and lead
Clinical Presentation
The most common presenting symptom of MR, when identified after the age of 2 years, is language delay. Before 18 months of age, the most common presenting feature is delayed achievement of gross motor milestones.
Gross motor delay does not predict MR, nor is gross motor delay seen in most children with MR. In most children with mild to moderate MR, the early motor milestones are normal. The issues are the following:
Most parents and professionals are best at recalling gross motor milestones.
Language skills are still rather rudimentary before 18 months.
Accurate testing of cognition is extremely difficult during the first few years of life.
The age at which delay in cognitive development first becomes apparent usually correlates with the degree of MR:
Identification before 2 years of age predicts severe or profound MR.
Identification after 2 years of age predicts moderate to mild MR.
Mild MR and borderline intelligence may not be recognized until a child enters school.
In children with structural anomalies, neurocutaneous or metabolic disorders, or syndromes associated with dysmorphic changes that are apparent prenatally or at birth, MR can be diagnosed very early, but only a small percentage of the total population of children with MR are affected by such conditions. Neurologic abnormalities are frequently associated with MR. Neonatal coma or intractable seizures are strongly related to abnormal developmental outcomes. Other neurologic signs are more common but less specific. Abnormal muscle tone, difficulty in feeding, seizures, and gross motor delays (neurologic soft signs) all serve as markers of developmental dysfunction. Abnormal muscle tone on evaluation warrants an assessment of other aspects of brain function, although muscle tone by itself is not believed to be directly related to cognition.
Diagnosis
There is no single gold standard for the medical evaluation for children with suspected or proven MR. Evaluation should be directed by patient history and physical examination, and a family pedigree. Possible considerations include the following:
Audiologic, vision, and speech/autism screening should be done in all children suspected of having MR.
Periodic screening for serum levels of lead and testing for anemia should be performed when indicated.
Children with confirmed serum levels of lead between 10 and 20 μg/dL have been shown to score two to five points lower on standardized IQ testing when other variables are controlled.
Dysmorphic children or children with a significant family history of developmental delay should undergo chromosomal studies (include testing for fragile X syndrome if most of the affected family members are male).
The number of dysmorphologic features is not predictive of IQ unless neuroimaging shows abnormalities of the gray matter.
Children with signs of motor delay and cognitive delay or failure to thrive may benefit from studies done to assess for inborn errors of amino acid or organic acid metabolism.
Weakness or floppy muscle tone should suggest the possibility of muscular dystrophy, in which case a serum creatine phosphokinase or aldolase determination may be diagnostically helpful.
Thyroid screening should be considered if indicated by growth changes or symptoms.
Electroencephalography, computed tomography, and magnetic resonance imaging (MRI) are generally reserved for children with asymmetric findings on neurologic examination, weakness, seizures, abnormal head growth, blindness, deafness, or other changing impairments. However, MRI evaluations yield subtle findings of cerebral dysgenesis in children who present with MR or learning problems, even when their neurologic examination findings appear normal. Abnormalities of cerebral migration or subtle anatomic changes may have a genetic basis. In such cases, notification of the family is warranted, and the recommendations regarding imaging studies in children with MR may be changed, even when no imminent clinical action is taken based on the results of the studies.
When considering laboratory and imaging evaluations for underlying etiologies of intellectual impairment, the following statistics are pertinent:
Specific etiology of mild mental retardation is identifiable in <50% of individuals. A definite genetic cause is found in about 5% of mild MR although familial clustering of individuals of MR is common.
Mothers who never completed high school are four times more likely to have children with mild MR than mothers who completed high school.
A definite genetic cause can now be identified in about 50% of severely mentally retarded individuals. There are more than 500 chromosomal and nonchromosomal dysmorphic syndromes associated with intellectual impairment. These are updated and found listed at the National Institute of Health website at http://www.ncbi.nlm.nih.gov/omim.
Down syndrome, Fragile X, and fetal alcohol spectrum disorder together account for about 1/3 of all identifiable causes of severe intellectual disabilities.
Recurrence risk in families with one child with severe intellectual disability of unknown origin is 3% to 9%. Known origin risks vary with the cause.
Comorbidities
Neurobehavioral disturbances resulting from disordered neural functioning, although not unique to MR, are a frequent accompaniment. During infancy, these disturbances may present as excessive colic, inconsolability, disturbed interactional abilities, or disturbances in the sleep-wake cycle.
Strauss syndrome, which is characterized by attentional disturbance (either too short or perseverative), distractibility, impulsivity, and temper tantrums, may present in preschool children with MR. Although mildly retarded children may resemble those with classic hyperactivity, more significantly retarded children do not resemble children with ADHD clinically. Bruxism, rocking, or other perseverative motor behaviors and self-injurious or aggressive behaviors are characteristic of expanded Strauss syndrome. These are seen in more severely retarded children. However, it should be recalled that head banging, bruxism, and similar behaviors are seen in normal children also.
Secondary emotional problems may arise when children are unable to cope with familial, educational, or peer expectations.
Engaging in oppositional behaviors to avoid failure or frustration is also a common presentation of MR during the preschool and early elementary school years. Aggression, self-abusive behavior, and psychiatric disorders are a greater detriment to successful integration into the community than decreased cognitive functioning per se.
Speech, language, and hearing disorders, seizures, motor impairments and/or CP, sleep disorders, and visual disorders are also seen often in children with MR.
Prognosis
In most children with MR (i.e., 85%-90% of affected children), the condition is mild, and they can be expected to live independently, read at a fourth to sixth grade level, maintain a competitive semiskilled job, and be physically and psychologically capable of parenthood.
Children with moderate MR may require some degree of support and supervision as adults (usually in a supportive extended family setting or supervised group home).
They have academic skills that range from prekindergarten to third grade level.
They have academic skills that range from prekindergarten to third grade level.
Adult outcome cannot be predicted by IQ alone because it does not account for social adaptation and functioning (both of which have a tremendous effect).
CEREBRAL PALSY
The features of cerebral palsy (CP) are summarized in Table 39.2.
Etiology and Epidemiology
CP is defined as persistent impaired motor function or posture that is evident at birth or becomes evident during early infancy. It is not progressive (i.e., it is a static encephalopathy, although the clinical manifestations may evolve and/or change over the course of the child’s lifetime) and usually not genetic, although it may be part of a genetic syndrome. If it is unclear whether a child’s condition is nonprogressive, the child should not be given a diagnosis of CP. Gross or microscopic changes in the brain are found in <50% of affected patients. Also, although the definition of CP is defined as motor control problems, the white matter CNS injury is associated with more subtle gray matter effects that can impact learning and cognition in children with cerebral palsy.
TABLE 39.2 SUMMARY OF CEREBRAL PALSY | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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The overall incidence in the general population is 2 to 3 in 1000 live births. The prevalence is 1.4 to 2.4/1000 children by early school age. The incidence in preterm infants is inversely proportional to their gestational age. Children born prematurely currently represent about one half of the children newly diagnosed with cerebral palsy.
Although the cause is unknown in most cases, risk factors include:
Intraventricular hemorrhage into the germinal matrix/ periventricular leukomalacia
Apgar score of 3 or lower at 10 minutes
Hypoxic-ischemic encephalopathy in very few cases
Congenital brain malformations
Chromosomal abnormalities and certain syndromes
Intrauterine growth restriction
Postnatal events (e.g., meningitis or brain trauma)
Premature birth before 28 weeks
Multiple gestations
Fetal infections (cytomegalovirus, toxoplasmosis)
Maternal chorioamnionitis or hypercoagulopathies
Clinical Presentation
Spastic diplegia presents initially with hypotonia, and delay in sitting, standing, and ambulating is typical. Sixmonth-old children who are floppy with brisk deep tendon reflexes in the lower extremities, fall backward when
attempting to sit, and stiffen from the top of the head down through the hips and knee to support their weight on tiptoe when attempting to stand, are likely to have spastic diplegia.
attempting to sit, and stiffen from the top of the head down through the hips and knee to support their weight on tiptoe when attempting to stand, are likely to have spastic diplegia.
In children with spastic quadriplegia, all four extremities are affected with tightness and exaggerated reflexes, and the incidence of associated neurobehavioral problems, such as seizures, MR, strabismus, and oral motor dysfunctions, is higher. Spastic hemiparesis commonly becomes evident when asymmetries in tone or reflexes develop, usually after 4 months of age. Parents may note fisting on the affected side or early handedness. Late crawling or dragging one leg with an asymmetric push-off or support with the upper extremities may also be the presenting complaint. The full extent of spasticity and motor deficit may not be apparent until 3 years of age.
The child with athetoid CP may demonstrate hypertonicity very early, which then appears to resolve by 3 months of age. The motor milestones are delayed by floppiness in the presence of normal deep tendon reflexes. An obligatory asymmetric tonic neck response may be present. By 10 months of age, the child may use raking movements rather than the expected pincer grasp, but it is not until 12 to 18 months of age that involuntary dystonic pos-turing is manifested during voluntary attempts at movement. Around this age, the hypotonia evolves into rigid or cogwheel hypertonicity.
The ataxic type of CP presents with hypotonia of the trunk and extremities, but the deep tendon reflexes are normal. When ambulation is attempted, children lock their knees in hyperextension and use a broad-based gait to assist with balance. Walking is late, but it is rare to see head titubation or intention tremor during infancy.
Diagnosis
The diagnosis of CP is difficult to ascertain before 6 months for the following reasons:
Most movement in normal infants at this age is under reflexive control, not cortical (volitional) control.
Transient abnormalities in tone resulting from perinatal insults may resolve or at least change during the first year of life; for example, many children with eventual spastic diplegic CP are initially hypotonic for several months.
Tone, primitive reflexes, and deep tendon reflexes are the mainstays of physical diagnosis in CP.
During infancy, tone can be assessed by placing the infant in prone, supine, and suspended prone positions as well as in supported sitting and standing positions. Alternatively, one can assess the passive range of motion of the joints, or the active range of motion of the reflecting muscle groups (i.e., flexor/extensor, adductor/abductor). Newborns held in prone suspension should demonstrate flexor posturing of the trunk and extremities. By 6 weeks, the head should be even with the body, and slightly less flexion of the arms and legs should be noted. If the head is hyperextended or the legs extend upward above the plane of the body, hypertonus is present. In vertical suspension, scissoring of the lower extremities after 2 months is also evidence of increased hip adductor tone.
Primitive reflexes can also provide clues to abnormal maturation of voluntary muscle control.
The asymmetric tonic neck response should never be obligatory. (Roughly translated, this means that the response lasts for more than 30 seconds.) Persistent evidence of even a nonobligatory asymmetric tonic neck response beyond 6 months of age strongly suggests central nervous system (CNS) damage.
Persistence of the Moro response beyond 6 months or absence of righting responses or parachute protective responses beyond 12 months strongly suggests abnormal maturation of the CNS voluntary movement pathways.
If a deep tendon reflex is increased or clonic, or if the area over which percussion can elicit a reflex is exaggerated, upper motor neuron injury is likely.
The classification of CP is based on the type of motor disorder, not on the cause. Four types are described, and a mix of the types is found in 20% of patients. The types are as follows:
Spastic or pyramidal (65%)
Dyskinetic or extrapyramidal (25%)
Ataxic (5%)
Hypotonic (5%)
In the spastic or “pyramidal” type, the upper motor neurons are involved. The characteristics are weakness, increased muscle tone, increased deep tendon reflexes, clonus, “clasp-knife” tightness or spasticity, extended and “scissored” (crossed) legs, and a tendency to develop contractures. This type may be further divided according to the areas of the body that are affected. In quadriplegia (also called quadriparesis), all four limbs are involved, whereas in diplegia both legs are involved primarily, with minimal arm involvement. The diplegic form is the most common; it is frequently seen after intraventricular hemorrhage or is associated with the development of periventricular leukomalacia. The incidence of both of these conditions (intraventricular hemorrhage and periventricular leukomalacia) is increased in association with a younger gestational age in premature infants. In hemiplegia, both limbs are involved on the same side.
The dyskinetic or extrapyramidal type causes abnormalities in muscle tone and consists of several subtypes: an athetotic form, chorea, dystonia, tremor, and rigidity. The athetotic form, the most common subtype in this category, involves impairment of volitional movements. Uncontrolled and purposeless movements are evident when the child is awake but disappear during sleep. Previously, the most frequent cause was hyperbilirubinemia/kernicterus, but at present it
is hypoxic-ischemic encephalopathy (with resultant damage to the basal ganglia). The other subtypes are as follows:
is hypoxic-ischemic encephalopathy (with resultant damage to the basal ganglia). The other subtypes are as follows:
Chorea: rapid, irregular limb movements
Dystonia: slow twisting of the proximal limbs, neck, and trunk
Tremor: alternating contractions
Rigidity: contractions in the flexor and extensor muscles
The ataxic type of CP is characterized by gait imbalance and incoordination. The most common cause is hydrocephalus or various genetic syndromes.
The hypotonic type may evolve into one of the three other types.
Comorbidities
MR is a comorbid factor in 50% to 60% of the cases. The incidence varies with the type of CP: 40% in patients with hemiplegia and 70% in those with quadriplegia. Of affected children, 15% have mild MR, 35% moderate MR, and 50% severe MR. Hearing deficits occur in 30% of cases of CP, mostly in children with the athetoid form, because of the association with hyperbilirubinemia. Seizures occur in 30% to 50% of cases, most commonly in hemiplegic children, least often in the athetoid form. Drooling is most common in children with involvement of the pseudobulbar system. Visual deficits, feeding and associated growth abnormalities, and behavioral and emotional disorders are also seen.
Treatment
Therapies to address the functional implications of difficulty with voluntary movement are the mainstays of treatment in CP. The goals of therapy are to:
Establish mobility and prevent contractures by the use of orthoses and antispasticity treatments.
Address communication problems in patients with dysarthria, dyspraxia, or central language disorders. (Manifestations of pseudobulbar palsy are often associated with athetoid or spastic forms of CP.)
Correct visual deficits or strabismus (seen in as many as 75% of children with spastic types of CP).
Control seizures.
Obtain appropriate educational assistance for children with cognitive disorders.
Prevent secondary emotional or health-related problems (failure to thrive or later obesity in nonambulators).
Multiple modalities are used to aid in the management of spasticity. These include serial casting techniques (which involve the use of casts to progressively stretch and increase the range of motion across a contracted joint), neurosurgical techniques (such as selective dorsal root rhizotomy, the more traditional approaches involving physical therapy), and orthopaedic interventions to lengthen or realign tendons. Each of these modalities requires ongoing follow-up and close communication among team members to optimize functional outcomes. Pumps placed intra-abdominally with a tunneled catheter can be used to deliver baclofen to the intrathecal space, and the injection of botulinum toxin into overactive muscle groups may also reduce spasticity. Other oral medications, such as baclofen, diazepam, lorazepam, clonazepam, and dantrolene may also provide benefit.
Pediatric anticipatory guidance can help families focus on fostering an independent, resilient young individual with good social skills and at the same time attend to the complicated medical and surgical aspects of addressing motor disability.
MYELOMENINGOCELE
The features of MMC are summarized in Table 39.3.
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