Developmental Delay: How to Diagnose, Plan Exclusions
Janice Cockrell, M.D.
Developmental delay is a term applied to a wide range of disorders, including mental retardation, motor delays, developmental language delays, developmental coordination disorders, autism spectrum disorders and global developmental delay. Before modern imaging and genetic studies, the term described any child not achieving developmental milestones and in whom a medical diagnosis had not been identified. Previously a developmental diagnosis consisted of a careful history, family history and physical examination, which included evaluation of a child's function in the cognitive, gross motor, fine motor, language and social domains and determining if function was within two standard deviations in each domain.
The availability of conventional magnetic resonance imaging (MRI) has been useful in delineating structural abnormalities and injuries, but magnetic resonance spectroscopy (MRS) has been able to demonstrate abnormal myelination patterns in children with isolated developmental delay (1). Newmeyer and colleagues investigated children with global developmental delay using MRS and identified brain creatine transport deficiency in 2 of 14 children, and identified structural and white matter abnormalities in the remaining 12 (2).
Genes and environment interact
Evaluating the etiologies and natural course of developmental disabilities has been challenging due to the interaction of genes with environmental factors, hence the nearly infinite number of variables which makes the study of the natural history and intervention outcomes so difficult (3).
In 2001 a retrospective study attempted to identify the etiology of developmental delay in 224 children less than 5 years-of-age referred to the developmental or neurology clinics of Montreal Children's Hospital. Although yield varied across the subtypes, in a high percentage of the children a medical etiology was identified, particularly in the cases of global and motor delays (4). With more sophisticated imaging and laboratory studies available, the yields would no doubt be higher in a similar prospective study done today.
Treatment
Having determined that the majority of developmental disabilities are a result of a medical condition or injury, the next question regards treatment. In some particular delays due to inborn errors of metabolism, a pharmacologic approach is possible. However, in most cases, where there is structural damage to the brain, the only option are rehabilitative or habilitative. Rehabilitative therapies are designed to restore previous levels of function. However, a developing child is a dynamic organism, and functioning in the various domains is expected to progress, just as height and weight increase throughout childhood and adolescence. Thus, in pediatrics, therapy must be not only rehabilitative, but also habilitative so the child progresses through the developmental continuum (5).
Plasticity is evident in both neuronal and non-neuronal tissues (6). In their review, Dong and Greenough cite recent studies which indicate that environmental and experiential intervention can reduce or ameliorate some of the neuronal and non-neuronal abnormalities present in childhood neurological or developmental disorders. While high quality research in natural history and intervention outcomes is difficult, certain trends are becoming clear: the earlier and more intensive and comprehensive the intervention, the more successful it is. Ramey and Ramey reviewed the history of early intervention efforts and concluded that fragmented, weak efforts were likely to fail, whereas intensive, high-quality, ecologically pervasive interventions are likely to be successful (7). Rappaport and colleagues found evidence that occupational and speech therapy intervention in preschoolers appeared to decrease the incidence of Attention Deficit Hyperactivity Disorder (8).
Conclusion
In summary, developmental disabilities are usually the result of a genetic abnormality or a central nervous system injury which has occurred prenatally or in early childhood. Children's brains demonstrate a great deal of plasticity and are therefore amenable to negative and positive environmental influences. Because the human brain does not achieve maturity until the mid-twenties, when neuronal adaptation becomes more difficult, rehabilitative efforts must focus on the restoration of previous functional levels and the achievement of important developmental milestones. These efforts are most successful if they are early, intensive, and comprehensive.
Literature Cited
1 Fayed N, et al: White matter proton MR spectroscopy in children with isolated developmental delay: does it mean delayed myelination? Academic Radiology 13(2):229-35, 2006.
2 Newmeyer A et al: Incidence of brain creatine transported deficiency in males with developmental delay referred for brain magnetic resonance imaging. Journal of Developmental & Behavioral Pediatrics 26(4):276-82, 2005.
3 Levitt P. Developmental neurobiology and clinical disorders: lost in translation? Neuron 46(3):407-12, 2005.
4 Shevell MI, et al: Etiologic determination of childhood developmental delay. Brain & Development 23(4):228-35, 2001.
5 Stiles J, et al: Cognitive development following early brain injury: evidence for neural adaptation. Trends in Cognitive Sciences 9(3):136-43, 2005.
6 Dong WK, Greenough WT: Plasticity of nonneuronal brain tissue: roles in developmental disorders. Mental Retardation & Developmental Disabilities Research Reviews 10(2):85-90, 2004.
7 Ramey CT, Ramey SL: Early intervention and early experience. American Psychologist 53(2):109-20, 1998.
8 Rappaport GC et al: Is early intervention effective in preventing ADHD? Israel Journal of Psychiatry & Related Sciences 35(4):271-9, 1998.
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