PREVALENCE OF DISABILITIES
Early diagnosis of developmental delays improves the outcome for children and families by preventing secondary understimulation or excessive pressure, utilizingavailable strengths and community resources and making genetic counseling possible.1 Routine screeningby pediatricians is an effective method for achieving early diagnosis of developmental defects and sensory impairments."
What are the conditions which can be identified by early developmental screening and how prevalent are they? The major categories are mental retardation, cerebral palsy, deafness, blindness, language impairment and emotionalbehavioral disturbances, the most severe of which is childhood autism (Table I).
Mental retardation is defined as "significantly subaverage general intellectual functioning existing concurrently with deficits in adaptive behavior and manifested during the developmental period."1 A prevalence of 2.5% was found among the 9, 10, and 11 year olds in the comprehensive Isle of Wight study.
Nelson and Ellenberg5 defined cerebral palsy as a "chronic disability characterized by aberrant control of movement or posture appearing early in life and not the result of recognized progressive disease." Children with major malformations of the central nervous system were excluded. Using the data from the National Collaborative Perinatal Project, they found a prevalence of 5.2/1,000 at 7 years of age."
The prevalence of blindness and significant visual impairment among school age children is 2/ 1000. 6 Profound congenital hearing loss isfoundinl in600or800 normal newborns.7 Developmental speech /language disorder is manifested by a"delay in development which is out of keeping with the child's general level of intelligence, which is not associated with a gross hearing loss or any overt neurological condition and which is associated with a normal social usage of the language available to the child."8 Among physically healthy children of normal intelligence, slightly less than 1 / 1000 have language delay which is still handicapping when they enter school.
Behavior problems are a frequent part of the clinical picture of children seen in pediatricians'1 offices and in developmental evaluation centers. These problems are not rare among preschoolers regardless of developmental status. A survey involving a random sample of London 3 year olds found that about 7% had behavior problems of moderate to marked severity and 14% had mild problems. The most common clinical picture was of a child who was active, attention seeking, disobethent and difficult to manage.9 Childhood autism is a rare and fascinating disorder characterized by profound failure to develop social relationships, a form of language retardation and various ritualistic or compulsive phenomena. About 4/10,000 children manifest childhood psychosis and about half of them have childhood autism.10
Only behavior problems are more common than mental retardation, and all other conditions are considerably less frequent. All of the conditions listed can be associated with mental retardation, except developmental speech/language impairment which specifically excludes retardation. There is no screening instrument in current use which focuses specifically on behavior and emotional development.
APPROXIMATE PREVALENCE RATES OF DEVELOPMENTAL DISABILITIES
IDENTIFICATION OF DISABILITIES
Young children are referred for developmental evaluation because either the parent or the primary physician is concerned about them (Table 2). If they are stigmatized, their problem may be identified at birth, as is true of most children with Down's syndrome. But if their appearance is normal, then the usual parental complaints at 0-2 years are delay in walking or other motor skills, and at 2-5 years delay in talking and/or difficult behavior. As a general rule, the more severe delays manifest at a younger age.
Pediatricians are alerted to possible developmental problems by a history of risk factors or delayed milestones, by stigmatized appearance or abnormal neurological findings on examination, and by metabolic or developmental screening.
Prenatal factors known to increase the risk for developmental disabilities are maternal illnesses, infections and teratogens. Alcohol and narcotics are import ant examples of the latter. Low birth weight infants, particularly those under 1500 gms,constitutea well known very high risk group, whether they are preterm or small for gestational age and, particularly, when both factors are present. Among low birth weight children, the groups known to have more than 10% risk for major neurological or cognitive sequelae are all children under 1 500 gms and children weighing 1501 to 2500 gms with either bronchopulmonary dysplasia, postasphyxia seizures or meningitis. Children with birth weights under 1500 gms who are also small for gestational age, have a 30-50% risk. Among children weighing over 2500 gms, only postasphyxia seizures or meningitis lead to a 1 0%risk of handicap.11 Low Apgar scores are risk factors for cerebral palsy, but it is noteworthy that in the Collaborative Perinatal Project only 45% of children with cerebral palsy had Apgars of 0-6 at 1 minute.12
A family history of retardation, speech delay or other developmental problems should always besought. Parents are more likely to respond in the affirmative, if (heir own statement of the chief complaint is used inthequestion(i.e, "speech delay" or "nervousness"). Educational level and literacy of both parents also need to be ascertained. In obtaining a developmental history, motor milestones are recalled more accurately than language milestones.13 Since, by age 3 years, the vast majority of children have intelligible speech understood by strangers, it is useful to inquire about this achievement.
Children who are overtly stigmatized are usually identified early and evaluated for the presence of chromosomal anomalies or other syndromes which may be associated with mental retardation. The presence of a few minor stigmata should also lead to a closer look at the child's development, since an excess of minor physical anomalies has been reported in association with idiopathic mental retardation14 and hyperactivity.15 Examples of the physical anomalies described are: two or more whorls, inner epicanthal folds, hypertelorism, low set or malformed ears, a high arched palate, incurved fifth fingers, single transverse palmar creases, third toes longer than the second and syndactyly of the two middle toes. However, stigmata alone should not be assumed to indicate intellectual deficit.
The diagnosis of cerebral palsy is made on the basis of a finding of motor delays associated with abnormalities of tone, posture, and the persistence of primitive reflexes. Most retarded children do not ha ve significant abnormalities on neurological examination, though coordination deficits are sometimes found. Drillien16 has described a syndrome of "transient dystonia" occurringin the first year of life among children of low birth weight. It consists of increased tone, exaggerated and/or prolonged primitive reflexes and retarded development which resolves by one year of age, but is subsequently associated with an increased incidence of mental impairment and hyperactive behavior.
A rational approach to determining the etiology of mental retardation in any child is based on differentiating whether the probable insult was a prenatal problem of morphogenesis, perinatal brain damage, or due to postnatal onset of brain dysfunction.17 A careful history will reveal perinatal or postnatal onset, while the presence of stigmata or small size for gestational age points to a prenatal etiology. Children with inborn errors of metabolism usually have normal appearanceand function at birth, with subsequent deterioration. However, with the expansion of newborn screening programs, conditions such as histidinemia and cystinuria are being identified at birth.18 Moderately and severely retarded children are more likely to have identifiable medical conditions, delayed milestones and to be stigmatized and clumsy. Mildly retarded youngsters, on the other hand, more frequently have a family history of academic limitations or adverse social circumstances.
IDENTIFICATION OF DEVELOPMENTAL DISABILITIES
Identification of developmental delays is made earlier, particularly in children who are normal in appearance and in motor development, when developmental screening is used as part of routine well child care. The Denver Developmental Screening Test (DDST) is a commonly used tool which has been well validated. In a study comparing results on the DDST with full psychological testing using either Bayley Scales of Infant Development19 or Stanford Binet Intelligence Scales,20'21 81%of children were correctly identified by the DDST. Most of the errors were in thedirection of over-referral of normal children for evaluation. However, in the few instances where abnormal children were not identified by the DDST, the probable cause of the discrepancy was the use of parental reports on the DDST, while the psychological tests are based only on observation. For children from four to six years, additional screening instruments may be needed, since the DDST is not as sensitiveat this age range as for the younger group.2
The literature reports that mildly retarded children are usually identified at school age.22 However, in our experience as the developmental evaluation referral center for a pediatrie clinic where the Denver Developmental Screening Test is routinely used, mildly retarded children are identified in preschool age. Our clinical impression is that screening has had its greatest impact on earlier identification of healthy, motorically intact, unstigmatized, mildly retarded children. These young mildly handicapped children are a group which show a good response to intervention.
Developmental screening by pediatricians serves an additional purpose besides early identification. The act of screening states to the parent that the pediatrician's role includes knowledge of, and interest in, the child's development and behavior. The findings on the screening, when normal, are a natural introduction to individualized anticipatory guidance.
If the screening results are abnormal, the physician requires special skill in discussing what this means and what should be done. For the parent, this discussion is a difficult first step in coming to terms with the possibility of developmental disability in the child. It is known from other screening programs that being identified as abnormal by screening is stressful. When a diagnostic test can confirm or deny the screening findings, needless anxiety can be dispelled quickly. However, developmental evaluation is a slower and sometimes less definitive process than laboratory tests. In addition, since developmental screening is not a search for a hidden cause of disability but a means of early identification of actual delays, parents have often had some concern about their child before the screening. Optimal handling of the referral requires that the pediatrician learn the parents' views on their child's current function in order to assess whether the plan for a diagnostic referral will come as ashock. The most common errors made are: minimizing the problem and giving the reason for referral as immediate intervention rather than evaluation (e.g. "your child's speech is a little delayed, I'll send him for therapy") and making a diagnosis based only on screening, (e.g. telling the parent who came for a well child visit that her child is retarded). Optimally, the pediatrician should explore the parents' perceptions, state his concern, the need for further evaluation and appropriate management, and indicate his intention to continue to follow the child's progress and to guide the parents using the information obtained at the evaluation.
PSYCHOLOGICAL EVALUATION, USE AND LIMITATIONS IN YOUNG CHILDREN
The function of psychological testing is to establish an accurate level of current performance for the purpose of diagnosis, prognosis, planning of intervention, and as a baseline to measure future progress. The Denver Developmental Screening Test and other screening tools differ from psychological testing in their purpose and the degree of insight they provide. Screening tests such as the DDST were principally designed to select children who fall below age expectancy and will need more comprehensive workups.23 Labelling and the planning of a special program should never be based on screening alone.
The uses and limitations of psychological tests are dependent on the child's age, degree of deviation from normal and nature of associated handicaps. Children from birth to 2 years are identified by pediatricians as delayed if they have medical conditions associated with retardation, motor or sensory handicaps, or significant delays of unknown cause. Even with the use of developmental screening, the more severe delays manifest themselves earlier. At this age, the usual presenting complaints from the parents are "walking late" or "slow development."
There is considerable controversy over the predictive value of infant tests used for children up to 2 years (e.g. Catteli Infants Intelligence Scale,24 Bayley Scale of Infant Development,19 and Griffiths Mental Development Scales25). The predictive valueoftheseinfanttestsdepends on the intelligence level of the children tested. For infants testing in the average range or slightly below, the predictive value is poor. u However, for children whose functioning is markedly delayed, significant correlation has been consistently reported between infant test scores and future IQ and educational level. Drillien states that it is "much easier to predict mental dullness in infancy than mental superiority."27
The lack of correlation for the general population between infant test scores and future IQ and school achievement seems related to multiple factors including differences in the structure of infant tests and the abilities tested by them as compared to intelligence tests used for older children.26 Furthermore, these tests stress quantitative differences rather than qualitative ones which are important in human development. Piaget28 considered the progress from one stage to another a specific characteristic of human development, and a child makes significant qualitative progress from the sensorimotor to the representational stage.
Young children with motor handicaps such as cerebral palsy and those with blindness or deafness usually cannot be adequately tested with standard infant tests. For children who are very significantly retarded, testing below age 2 is mainly useful in providing the level of retardation. It is not needed for planning a stimulation program which can be accomplished more meaningfully by clinical observation using scales of sensorimotor development based on Piaget's theory.29 Infant tests provide a good measure of present developmental status and s co res which are useful for observing developmental changes. Because of these limitations of infant tests, some evaluation centers use only careful pediatrie developmental evaluations for this age group, and defer formal psychological testing to 2 years of age.
For children above the age of 2, failure on the Denver Developmental Screening Test is an unequivocal indication for formal psychological testing. For this age category, the parents' chief complaints are "not talking well" and/or behavior problems in a majority of cases. Psychological testing can determine the level of intelligence, areas of strength and weakness, specific learning difficulties and emotional-behavioral problems. Well standardized intelligence tests which assess both verbal and non-verbal abilities in preschoolers are: Stanford Binet Intelligence Scale, 20,21 McCarthy Scales of Children's Abilities,30 Wechsler Preschool and Primary Scale of Intelligence,31 Griffiths Mental Development Scales.32 Children with multiple handicaps and motor or sensory impairments can be tested at preschool age with special modifications of standard tests33 or with tests especially developed for a condition, for instance, the HiskeyNebraska Test with norms for the deaf.34 Minority group children also present a special problem, since the translation of the tests from English to another language affects the use of norms and the tests may have been standardized on different sociocultural groups.15
The psychological evaluation can be used as a basis for educational planning, therapeutic intervention, and parent guidance. At this age, correlation between present and future test scores increases significantly and becomes predictive even for children with average intelligence.26,36 All children tested for developmental problems in the preschool age need psychological re-evaluation at school age.
Labelling children as develop mentally abnormal has the inherent danger of becoming a self-fulfilling prophecy. It is essential to be cautious and diagnostically thorough before applying a label such as mental retardation or emotional disturbance, especially where the degrees of impairment are mild. The more strictly medical diagnoses such as cerebral palsy, blindness or deafness do not arouse as much professional controversy since the evidence for them is considered more objective. However, it is a truism that the label is the key to services. Free preschool programs of good quality may be available to children with the diagnosis of mental retardation or cerebral palsy, but not for those with borderline intelligence or marked clumsiness. Careful discussion of the diagnostic label, its use and limitations, with the parents is essential.
ISSUES IN DIAGNOSIS
Mentally retarded children who are stigmatized and low functioning in all areas of testing seldom cause diagnostic confusion. However, the test scores of mentally retarded children often show discrepancies in various areas of functioning, with cognitive abilities tending to score lowest.37 Children's appearance, motor development, the presence of language delay or behavioral/emotional problems are issues on which there are common misconceptions which can lead to errors in judgment.
According to Richardson,38 "there appears to be a widespread belief that mental retardation can be identified by physical cues." Stigmatization of appearance increases with the degree of retardation but is uncommon even in severely retarded children.39 A child who looks normal is usually considered by his parents to be normal and they are confused by his or her lack of age-appropriate skills.
Another common misconception is that motor milestones have good predictive value for future intellectual functioning. A child with delayed or atypical motor development needs careful neurological evaluation with particular emphasis on eliciting abnormalities of tone, posture, movement or the persistence of primitive reflexes which are seen in cerebral palsy. However, as Illingworth40 has noted, motor development is the area most easily scored and the least valuable for overall assessment of a child's cognitive capability. Data from the Newcastle Survey of Child Development reveals that 7% of the children in this population started walking independently after 1 7 months of age, and a great majority of this group had IQs well within the normal range.41 The proportion of children who begin walking later than expected increases with increasing severity of mental retardation. However, even severe degrees of retardation are compatible with normal onset of ambulation. A recent study of 200 young retarded children living in the community found that 80% of the mildly retarded children walked at thccxpectedage, as did the majority of those functioning at the moderately to severely retarded level.42 Retardation cannot be assumed to exist because walking is delayed, nor can normal onset of ambulation be used as reassurance of normal general development.
Delayed or inadequate speech and language development is a common presenting complaint in the 2 to 5 year age group. If the parents report delayed speech development they are almost invariably right, but that does not mean that their child's primary problem is language impairment. Of children presenting with the chief complaint of language delay, only half of the cases had a final diagnosis related to speech or language impairment following a full evaluation, while the other half of the group had a diagnosis of mental retardation.43 Children who show a delay in the language area on the Denver Developmental Screening Test should be referred for complete evaluation, and not only for speech assessment.
Evaluation of a child with delayed language development must always include an audiometrie evaluation to rule out even a mild degree of hearing loss. Subsequently, correct diagnosis requires careful assessment of all areas of development and behavior, using formal psychological testing as well as speech and language evaluation. A diagnosis of language impairment can only be made if the child has been shown to have normal hearing, significantly higher skills in performance items than in language and use of the language skills he possesses in interpersonal communication. The most frequent cause of delayed language is mental retardation, as would be expected based on the prevalence rates of the various conditions considered in the differential diagnosis. Autism is an extremely rare cause of delayed speech and language and can be diagnosed by history and observation of unrelated and ritualistic behavior. A majority of autisticchildrenare also mentally retarded.44
The significance of delayed language development may be controversial even when full psychological and language evaluations are available. Among children referred for evaluation, language is often t he lowest area on testing, especially during the preschool age. The nonverbal performance tasks for preschoolers have their limitations, since they consist mostly of items requiring fine manipulative skills, perceptual matching and imitation. They rarely include items involving representational and symbolic thinking which is tested by many verbal tests. Non-verbal skills and performance scores do not predict later functioning and academic achievement as well as verbal tests do.45
The language area is also less developed in children from low social class and in minority groups. Social class differences are not found within the sensorimotor stage (02 years) and are often seen to increase with age.46 The origin of differences in language development between social classes is thought to be based on differences in child rearing practices and types of parent-child interaction. The sty Ie in middle class homes is more reflective and verbal, while lower social class parents demonstrate a more actionoriented approach.47
Behavior problems are a common initial complaint among children seen for developmental evaluation and a significant proportion of children found to be retarded also manifest emotional or behavioral abnormalities. The most common symptom complex seen in preschoolers of all levels of retardation was hyperactive behavior with attentional deficits. Among the moderately to profoundly retarded children, autistic and unrelated behaviors were second in frequency, while this picture was rare among mildly retarded youngsters, who showed a full range of the emotional and behavioral disorders seen in the normal population.48
The most common group of maladaptive behaviors noted in unselected three year olds was being active, attention seeking and disobethent.9 These are the same behaviors, perhaps in an exaggerated form, that are seen among retarded preschoolers. Children who are functioning within the sensorimotor stage of development are more likely to respond to a situation by action or anxiety, rather than by using language to influence the outcome. Retarded children function at this action-oriented level beyond the expected age.
When parents are unaware of their child's inteilectual deficit, they often feel that the child is refusing to conform to their expectations, when he is actually unable. This misinterpretation of the child's motives can lead to frequent negative interactions, and more disorganized behavior. Any time a parent complains to a pediatrician that a child shows difficult behavior, at least a careful developmental screening should be performed before assuming that the child is normal, evenly functioning, and/or the problem is primarily interactional.
INTERPRETATION OF EVALUATION RESULTS
Effective developmental diagnosis requires the pediatrician to view the child's problem from two perspectives, the medical-etiologic as well as the functional or rehabilitative. The former is the classical medical model of disease requiring workup, which hopefully leads to an etiologic diagnosis and treatment based on the diagnosis. The physician's tools are based on this orientation. The classical neurological examination is designed to elicit abnormal findings, with particular emphasis on signs which help the physician to localize the nervous system lesion. Developmental screening and subsequent evaluation are complementary to this approach. These tests contain only items which normal children are expected to perform. They do not seek to elicit signs of deviance, but rather a functional level at which the child can currently perform tasks. They provide information analogous to the functional classification in cardiac disease and other chronic conditions.
Medical diagnoses for developmentally disabled individuals are sometimes a statement of etiology, at other times they merely describe an associated medical finding. The degree of relevance of the medical diagnosis to the developmental status varies. In well known genetic diseases such as Down's syndrome, the medical diagnosis explains the developmental deficit. More frequently the etiology of mental retardation is unknown and the relationship between the medical findings and the retardation is speculative. It is nevertheless worthwhile to seek these medical findings, since some conditions, such as strabismus, are treatable, and other medical abnormalities may eventually be shown to be part of a syndrome associated with developmental defect.
When a delay is identifiable by failure on adevelopment screening test, the intellectual handicap is seldom completely reversible, and etiologic diagnoses are useful mainly in ruling out progressive disease and for genetic counselling. However, this is not equivalent to saying that nothing can be done. Rather, treatment consists of education and individual therapies for the child and guidance and support for the parents.
The functional-rehabilitative diagnoses constitute the basis of such therapeutic intervention. The pediatrician has a major role in delineating the motor status of the child, with his involvement in describing other areas of functioning depending on the physician's background in child development. Based on the child's age and problems, functional evaluation will also include a psychologist, speech pathologist, physiatrist, neurologist, physical or occupational therapist, and psychiatrist. The child's emotional-behavioral characteristics are aspects of his functioning which should be noted by every professional who sees him, since this is a frequent problem area, and one which is amenable to intervention. A careful diagnostic evaluation is a valid statement of current function in all cases. The predictive validity of this statement will depend on the child's age, degree of deviance and associated deficits.
Last but not least, the family's capacity to respond appropriately to the child is a central issue in intervention. An analysis of the child's functioning is incomplete without an understanding of the family's capacity to elicit his strengths, help him compensate for his weaknesses and not become overwhelmed by the burden of his special needs.
Problems in communication between doctors on one hand, and schools and parents on the other, are often based on the fact that the doctor is addressing only the medical and etiologic issues, while the parents and other caretakers want clarification of the functional status. The physician is not expected to generate all the information on the functional diagnosis, but he is expected to explain how the medical findings relate to the developmental ones both in terms of etiology and current performance.
For example, a clumsy, distractible four-year-old boy was noted to be falling often in nursery school. History, chart review and examination revealed that the frequency of his falling at home was unchanged, his balance and coordination had always been below age expectation, while strength, sensation, tone and reflexes continued to be normal. With increasing age, and more available space in nursery school, he now had a wider motor repertoire and more opportunity to run and jump. However, he continued to be impulsive, distractible and clumsy, resulting in frequent falls in school. It was important for parent and school to have a doctor interpret the relationship between the neurologically based clumsiness and distractibility on one hand and the behavioral manifestation of frequent falls on the other.
The need for clearly interpreting medical findings in relation to developmental ones exists even when the findings are negative. It is a commonly stated parental misconception that a child cannot be retarded because his CAT scan or EEG or skull X-ray were normal, so there is nothing wrong with his brain.
Early diagnosis of developmental delays improves the outcome and the pediatrician often initiates this process by screening. However, his role extends beyond screening and search for etiology to the delineation of functional status, usually in conjunction with other disciplines. Even though much of the functional evaluation is performed by other professionals, it will remain the physician's responsibility to clarify the relationship between the medical findings, whether positive or negative, and the child's developmental status. The pediatrician will also continue to provide primary care and is therefore in a position to monitor the child's progress and provide ongoing support to the family.
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3. Grossman HJ. Manual on Terminology and Classification in Mental Retardation Washington: Publ American Association on Mental Deficiency 1977. p 11.
4. Rutter M, Graham P, Yule W. A Neuropsychiatric Study in Childhood. Clin Dev Med 35/36 London: SIMP-Heinemann. 1970.
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33. Haeussermann E. Developmental Potential of Preschool Children. New York: Grune & Stratton Inc, 1958.
34. Hiskey MS. Manual Hiskey-Nebraska Test of Learning Aptitude. Lincoln Nebraska: Union College Press. 1966.
35. Hertzig ME, Birch HG, Thomas A, Mendez OA. Class and Ethnic Differences in the Respomiveness of Preschool Children to Cognitive Demands. Monographs of the Society for Research in Child Development 33(1), Serial No 117, 1968.
36. Stott LH. Ball RS. Infant and Preschool Mental Tests: Review and Evaluation. Monographs of the Society for Research in Child Development 30(3), Serial No 101, 1965.
37. Zazzo R. Une recherche d'equipe sar la debilite meniate. Enfance, 4-5 SepDic. 1960, p 335.
38. Richardson SA. Reaction to mental subnormality. In Begab MJ, Richardson SA (eds): The Mentally Retarded and Society. Baltimore Universily: Park Press. 1975. p 86.
39. Tizard J. Individual differences in the mentally deficient. In Clark AM, Clarke ADB. Mental Deficiency. London: Methuen & Co Ltd.(Rep), 1961. p 156.
40. Illingworth RS. The Development of the Infant Young Child: Normal and Abnormal. Baltimore: The Williams and Wilkins Company, 1966, p 304.
41. Neligan G, Prudham D. Potential value of four early developmental milestones in screen ing children for increased risk of later retardation. Devel Med Child Neurol 11:423, 1969.
42. Jedrysek E. Kaminer R. Walking and retardation (in preparation).
43. Kaminer R, Jedrysek E. Developmental assessment of young children. Ambul Pediatr Prog Abstr 1980, p 58.
44. De Myer MK, et al. The measured intelligence of auiistic children. J Autism Child Schiz 4:42, 1974.
45. Wilson RS. Sensorimolor and Cognitive Development. In M i ni fie FD, Lloyd L (eds): Communicative and Cognitive Abilities. Baltimore: University Park Press. 1978, p 135.
46. Jensen AR. Bias in Menial Testing. New York: the Free Press, 1980.
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Requests for reprints should be addressed to Ruth Kaminer, M. D., Rose F. Kennedy Center. 1410 Pelham Parkway S., Bronx, NY 10461.
APPROXIMATE PREVALENCE RATES OF DEVELOPMENTAL DISABILITIES
IDENTIFICATION OF DEVELOPMENTAL DISABILITIES