In the diagnosis of milder grades of developmental delay, the possible effects of severe malnutrition, neglect and deprivation, chronic systemic disease, iodine deficiency, impaired hearing and vision, and possibly childhood psychosis should be considered. Of particular importance is the differentiation of a group of patients who are normal for a variable period after birth and then manifest a progressive decline from disease of the nervous system. This type of disorder is representative of the group of hereditary metabolic and degenerative diseases discussed in Chap. 36. Seizure disorders (and antiepileptic medications) can impair cerebral function, and several special childhood seizure disorders are associated with a progressive decline in mental function in this group of patients (see Chap. 15).
Management of Mild Developmental Delay
Because there is little or no possibility of restoring function to a nervous system that is developmentally or structurally damaged, the medical objective is to assist in planning for the patient’s training, education, and social and occupational adjustments. As Voltaire remarked long ago, guidance is needed more than education. Early multidisciplinary intervention is recommended and the parents must be counseled in forming realistic attitudes and expectations. Psychiatric and social counseling may help the family to maintain gentle but firm support of the patient so that he can acquire, to the fullest extent possible, self-help skills, self-control, good work habits, and a congenial personality.
Most individuals with an IQ above 60 and no other handicaps can live an independent life. Special schooling enables such patients to realize their full potential. Social factors that contribute to underachievement must be eliminated if possible. Later, there is need for advice about possible occupational attainments. Great care must be exercised in deciding about institutionalization. Whereas severe degrees of cognitive impairment are all too apparent by the first or second year, less-severe degrees are difficult to recognize early. As stated above, psychologic tests alone are not trustworthy. The method of assessment suggested many years ago by Fernald still has a ring of soundness. It includes (1) physical examination, (2) family background, (3) developmental history, (4) school progress (grade achieved), (5) performance in schoolwork (tests of reading, arithmetic, etc.), (6) practical knowledge, (7) social behavior, (8) industrial efficiency, (9) moral reactions, and (10) intelligence as measured by psychologic tests. All these data except (5) and (10) can be obtained by a skillful physician during the initial medical and neurologic examination and are used to guide the family in its difficult decisions.
The subject of developmental delay was introduced in Chap. 27, where it was pointed out that two major categories of this disorder have been delineated. In one, and by far the more common group, the cognitive limitation is relatively mild, allowing the individual to succeed with therapy and education; it is often familial and is featured by a lack of definite neurologic abnormalities (except possibly a slightly higher incidence of seizures) and the absence of neuropathologic changes. A large part of this group, falling between 2 and 3 standard deviations below the normal mean IQ, probably are the lower end of the Gaussian curve of intelligence, the converse of which is genius. This group is, however, contaminated with a small number of defined diseases of the nervous system occurring in a less-severe form. In a second group, the degree of developmental delay is usually more severe (IQ of 50 to 70), and yet more so in the third group (IQ less than 50 or not measurable because of limitations of cooperation or physical impediments). Most of the cases in the second and third groups are nonfamilial, and a wide variety of neuropathologic changes are in evidence. The subdivisions are not absolute, for there are a few metabolic and developmental diseases in which developmental delay is profound yet with no somatic or neurologic abnormalities and, most importantly, well-defined neuropathologic changes are lacking. Here we refer to conditions such as Rett syndrome, autism, and the X-linked developmental delay syndromes (Renpenning and fragile X types). In this chapter, these major types of severe developmental delay are described.