eMedicine Specialties > Neurology > Pediatric Neurology
Mental Retardation: Differential Diagnoses & Workup
Updated: Jan 11, 2010
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
Differential Diagnoses
Other Problems to Be Considered
Autism/pervasive developmental disorder
CNS trauma
Environmental deprivation
Major sensory deficits (eg, deafness, blindness)
Malnutrition
Mitochondrial cytopathies
Workup
Laboratory Studies
- No laboratory and/or radiologic investigation is routine in MR. The examiner must determine the nature and extent of the laboratory investigation following a history and physical examination.
- DNA analysis of the FraX promoter region should be ordered on all prepubertal males with MR, particularly if autistic features are noted. In the postpubertal period, the clinical manifestations of FraX are likely to be readily apparent, such that DNA analysis can be ordered with more selectivity in this population.
- Karyotype at the 500 band level of resolution (at least) should be considered in all children with MR.
- Chromosomal abnormalities (Tri 21 and others) may account for as many as 50% of those affected by severe to profound MR.
- Sex chromosome aneuploidy is seen in as many as 5% of children with mild MR or learning disabilities.
- FISH probes are ordered as clinically indicated, as follows:
- Prader-Willi/Angelman syndrome
- Smith-Magenis syndrome
- CATCH 22
- Williams syndrome
- Wolf-Hirschhorn syndrome
- Cri du chat syndrome
- Langer-Giedion (trichorhinophalangeal) syndrome
- Miller-Dieker syndrome
- Metabolic labs are ordered only as clinically indicated.
- Plasma amino acids (aminoacidopathies)
- Urinary organic acids (organic acidopathies)
- Urinary mucopolysaccharides and oligosaccharides (mucopolysaccharidoses)
- Plasma 7-DHC (Smith-Lemli-Opitz syndrome)
- Thyroid function tests
- Very-long-chain fatty acids (peroxisomal disorders)
- Creatine kinase (in the assessment of profound central hypotonia versus myopathy)
Imaging Studies
- Brain MRI
- Brain imaging should be conducted in any child with developmental delay and abnormal findings on neurologic examination, including abnormalities of head size and/or facial dysmorphisms.
- Brain MRI generally is preferred over CT scan, because the former has greater resolution and enhanced detection of abnormalities in the progression and timing of myelination, demyelination, and heterotopic gray matter.
- Head CT scan: This is the preferred imaging study for calcifications that may be identified with TORCH infections (ie, toxoplasmosis, other infections, rubella, CMV, herpes simplex), when tuberous sclerosis is suspected, or if craniosynostosis is a concern.
- Skeletal films: These assist with the phenotypic description, syndrome characterization, and assessment of growth.
Other Tests
- Detailed psychological assessment by a licensed psychologist is necessary to confirm the diagnosis of MR. Some of the most commonly used psychological tests in children include the following:
- Bayley Scales of Infant Development
- Normalized for ages 2-30 months
- Subtest scores for receptive and expressive language, nonverbal problem-solving ability, and sustained attention
- Stanford-Binet Intelligence Scale
- Normalized for ages 2 years to 23 years
- Fifteen subtests for assessment of 4 key areas of cognitive proficiency: verbal reasoning, abstract/visual reasoning, quantitative memory, and short-term memory
- Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R)
- Normalized for ages 3 years to 7.25 years
- Twelve subtests for assessment of verbal and nonverbal intelligence
- Wechsler Intelligence Scale for Children–IV (WISC-IV)
- For ages 6 years to 16 years, 11 months
- Verbal and nonverbal intelligence scores derived from 12 subtests
- Vineland Adaptive Behavior Scales
- For neonates to adults
- Measures ability to perform daily activities required for personal and social sufficiency; adaptive or functional behaviors rated by interviewing the child's guardian
- Deficiencies in at least 2 areas of adaptive skills required to meet the MR diagnostic criteria
- Bayley Scales of Infant Development
- Electrophysiologic studies
- EEG, if clinically warranted
- Auditory evoked potentials in the context of audiologic assessment
- Visual evoked potentials in cases of profound delay and suspected cortical blindness
Histologic Findings
Pathologic analysis of cortical tissue by the Golgi method in the 1970s suggested that in cases of profound, unclassified MR, dendritic spines were decreased and/or had immature morphology. These findings have been confirmed in cortical autopsy material from individuals with Down syndrome and FraX. Dendritic spine morphology is related directly to the intradendritic microtubular components and their organization.
Microtubules in dendrites of cortical neurons often are fragmented or in disarray in cases of developmental failure. In contrast, in some neuronal storage diseases associated with impaired cognition, dendritic spines are sprouted exuberantly beyond the developmental period and in ectopic locations. A relationship is implied, then, between dendritic spine morphology and number and cognitive development in the human.
More on Mental Retardation |
| Overview: Mental Retardation |
 Differential Diagnoses & Workup: Mental Retardation |
| Treatment & Medication: Mental Retardation |
| Follow-up: Mental Retardation |
| References |
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Further Reading
Keywords
cognitive impairment, intelligence quotient, IQ less than 70, learning disability, Down syndrome, Fragile X syndrome, Prader-Willi syndrome, Angelman syndrome, Smith-Magenis syndrome, CATCH 22 (22q11 deletion) syndrome, DiGeorge syndrome, velocardiofacial syndrome, Williams syndrome, Wolf-Hirschhorn syndrome, Langer-Giedion syndrome, Miller-Dieker syndrome, tuberous sclerosis, Rubinstein-Taybi syndrome, Coffin-Lowry syndrome, Rett syndrome, Smith-Lemli-Opitz syndrome, fetal alcohol syndrome, fetal alcohol effects, cretinism, congenital hypothyroidism, congenital cytomegalovirus, congenital rubella, intraventricular hemorrhage, hypoxic-ischemic encephalopathy, traumatic brain injury, shaken baby syndrome, meningitis
