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September 15, 2009 — A new Practice Parameter counsels neurologists on how to evaluate the child with microcephaly for the presence of neurologic and cognitive conditions. The document, prepared jointly by the American Academy of Neurology (AAN) and the Child Neurology Society, is published in the September 15 issue of Neurology.

"For physicians, this parameter is helpful because it has some terrific appendices that are on the AAN Website, and they have lots of succinct information about many of the different neuroimaging abnormalities that are seen with microcephaly, as well as metabolic diseases and genetic conditions," corresponding author Stephen Ashwal, MD, from the Loma Linda University School of Medicine, California, told Medscape Neurology.

The problem that a neurologist or pediatrician faces after they have made a diagnosis of microcephaly is how much testing to undertake to screen for causes and associated conditions, Dr. Ashwal said.

"That's where these appendices are very helpful, because in this document we have algorithms to help physicians with a clinical pathway to figure out whether they should do — or not do — certain tests, and then also provide guidance, based on history or physical features, [on] what genetic testing should be done," he added.

Common Problem

Microcephaly is common, affecting more than 25,000 infants in the United States each year, a release from the AAN notes. It is generally defined as a head circumference of more than 2 standard deviations below the mean for age and sex, and if not present at birth, it usually develops before 2 years of age.

Microcephaly can arise from any insult that disturbs early brain growth and is seen in association with hundreds of genetic conditions, the guideline authors write. Although it is an important neurological sign, there is no uniformity at this time in how it is defined or evaluated, although it can be associated with serious comorbid conditions, they note.

For this guideline, authors reviewed and classified the current literature and made recommendations based on a 4-tiered system. They found that few data are available at this time to make evidence-based recommendations about diagnostic testing in these children. The yield of neuroimaging ranges from 43% to 80%, they note.

Microcephaly arises from genetic etiologies in 15.5% to 53.3% of cases, the researchers report. The prevalence of metabolic disorders is unknown, they add, but is estimated to be 1%.

Children with severe microcephaly, defined as more than 3 standard deviations below the mean for age and sex, are more likely to have imaging abnormalities and more severe developmental impairments than those with milder microcephaly, the researchers report, with these conditions occurring in about 80% of those with severe microcephaly and about 40% of those affected more mildly.

About 40% of children with microcephaly also have epilepsy, 20% have cerebral palsy, 50% have mental retardation, and 20% to 50% have ophthalmologic and audiologic disorders, the authors write.

Based on their findings, their recommendations include the following.

• Level A recommendations:
  • Because children with cerebral palsy are at risk of developing acquired microcephaly, serial head circumference measurements should be followed.
  • Because children with microcephaly are at risk for developmental disability, physicians should periodically assess development and academic achievement to determine whether further testing and rehabilitative efforts are warranted.
• Level C recommendations:
  • Neuroimaging may be considered useful in identifying structural causes of microcephaly.
  • Targeted genetic testing may be considered to determine a specific etiology.
  • Because children with microcephaly are at risk for epilepsy, physicians may consider educating caregivers of these children on how to recognize clinical seizures.
  • Because these children are at risk for cerebral palsy, physicians and other care providers may consider monitoring them for early signs so that supportive treatments can be initiated.
  • Screening for ophthalmological abnormalities may be considered.
• Level U (insufficient evidence):
  • There is insufficient evidence to support or refute obtaining metabolic testing on a routine basis for the evaluation of the newborn or infant with microcephaly.
  • There are insufficient data to support or refute obtaining a routine electroencephalogram in a child with microcephaly.

Dr. Ashwal has disclosed that he serves on the scientific advisory board of the Tuberous Sclerosis Association and the International Pediatric Stroke Society. He also serves as an editor of Pediatric Neurology and receives research support from the National Institutes of Health. Disclosures for coauthors appear in the Practice Parameter document.

Neurology. 2009;73:887–897.