A delay in speech development may be a symptom of many disorders, including mental retardation, hearing loss, an expressive language disorder, psychosocial deprivation, autism, elective mutism, receptive aphasia and cerebral palsy. Speech delay may be secondary to maturation delay or bilingualism. Being familiar with the factors to look for when taking the history and performing the physical examination allows physicians to make a prompt diagnosis. Timely detection and early intervention may mitigate the emotional, social and cognitive deficits of this disability and improve the outcome.
Mental retardation is the most common cause of speech delay, accounting for more than 50 percent of cases.8 A mentally retarded child demonstrates global language delay and also has delayed auditory comprehension and delayed use of gestures. In general, the more severe the mental retardation, the slower the acquisition of communicative speech. Speech development is relatively more delayed in mentally retarded children than are other fields of development.
In approximately 30 to 40 percent of children with mental retardation, the cause of the retardation cannot be determined, even after extensive investigation.9 Known causes of mental retardation include genetic defects, intrauterine infection, placental insufficiency, maternal medication, trauma to the central nervous system, hypoxia, kernicterus, hypothyroidism, poisoning, meningitis or encephalitis, and metabolic disorders.9
Intact hearing in the first few years of life is vital to language and speech development. Hearing loss at an early stage of development may lead to profound speech delay.
Hearing loss may be conductive or sensorineural. Conductive loss is commonly caused by otitis media with effusion.10 Such hearing loss is intermittent and averages from 15 to 20 dB.11 Some studies have shown that children with conductive hearing loss associated with middle ear fluid during the first few years of life are at risk for speech delay.4,11 However, not all studies find this association.12 Conductive hearing loss may also be caused by malformations of the middle ear structures and atresia of the external auditory canal.
Sensorineural hearing loss may result from intrauterine infection, kernicterus, ototoxic drugs, bacterial meningitis, hypoxia, intracranial hemorrhage, certain syndromes (e.g., Pendred syndrome, Waardenburg syndrome, Usher syndrome) and chromosomal abnormalities (e.g., trisomy syndromes). Sensorineural hearing loss is typically most severe in the higher frequencies.
Maturation delay (developmental language delay) accounts for a considerable percentage of late talkers. In this condition, a delay occurs in the maturation of the central neurologic process required to produce speech. The condition is more common in boys, and a family history of “late bloomers” is often present.13 The prognosis for these children is excellent, however; they usually have normal speech development by the age of school entry.14
EXPRESSIVE LANGUAGE DISORDER
Children with an expressive language disorder (developmental expressive aphasia) fail to develop the use of speech at the usual age. These children have normal intelligence, normal hearing, good emotional relationships and normal articulation skills. The primary deficit appears to be a brain dysfunction that results in an inability to translate ideas into speech. Comprehension of speech is appropriate to the age of the child. These children may use gestures to supplement their limited verbal expression. While a late bloomer will eventually develop normal speech, the child with an expressive language disorder will not do so without intervention.13 It is sometimes difficult, if not impossible, to distinguish at an early age a late bloomer from a child with an expressive language disorder. Maturation delay, however, is a much more common cause of speech delay than is expressive language disorder, which accounts for only a small percentage of cases. A child with expressive language disorder is at risk for language-based learning disabilities (dyslexia). Because this disorder is not self-correcting, active intervention is necessary.
A bilingual home environment may cause a temporary delay in the onset of both languages. The bilingual child’s comprehension of the two languages is normal for a child of the same age, however, and the child usually becomes proficient in both languages before the age of five years.