Macrocephaly: WHO Growth Curves Misclassify Inuit Children

Using population-specific growth curves for Inuit children could promote the appropriate diagnosis of microcephaly and avoid overdiagnosis, according to a new study.
Inuit children from Nunavut, Canada, may appear to have high rates of macrocephaly, based on World Health Organization (WHO) growth chart measurements. But in many cases, no pathology is identified, and patients undergo unnecessary medical evaluation and burdensome travel.
Relevant growth curves that incorporate head circumference sizes slightly larger than the WHO standard could thus be useful for healthcare professionals, according to researchers.
“The idea for this study was sparked by the clinical observation of larger head sizes in Inuit children. Head size is one aspect of the physical exam that we neurologists pay close attention to, as it can be an indicator of different neurologic and genetic conditions,” lead author Kristina Joyal, MD, a pediatric neurologist at the University of Manitoba and University of Saskatchewan in Saskatoon, Saskatchewan, Canada, told Medscape Medical News.
“This is so important, especially for the children living in remote northern locations, because the medical assessments indicated for macrocephaly cannot be done locally and require significant family disruption to travel for multiple days, with multiple flights, to a larger medical center,” she said. “Furthermore, medical conditions associated with microcephaly may not be recognized as quickly, and the child may not receive the necessary medical assessment promptly.”
The study was published online on October 21 in CMAJ.
Distinct Growth Curves
Based on WHO standards, macrocephaly is defined as head circumference greater than the 97th percentile, while microcephaly is defined as head circumference less than the 3rd percentile.
The investigators analyzed head circumference data from their previous retrospective cohort study of the medical records of Inuit children in Nunavut. The study included children from birth to age 5 years who were born between 2010 and 2013 in communities with more than 20 births per year, which represented 18 of the 25 communities in the region.
In this study, to create a cohort of Inuit children similar to the cohorts used to develop WHO growth charts, the research team excluded children with preterm birth, documented neurologic or genetic disease, and most congenital anomalies. Then they compared the head circumference values of the Inuit cohort with those in the WHO charts.
The analysis included records for 1960 Inuit children, 50.8% of whom were girls. Most of the 8866 data points came from children aged 0-36 months.
Across all ages and genders, the Inuit study cohort had distinct growth curves, with significantly larger head circumferences than the WHO median measurements and lower rates of smaller head circumferences.
Overall, most z scores for Inuit head circumference measurements fell between 0.5 and 1 SD above the WHO reference. At 12 months, median head circumferences were 1.3 cm larger for Inuit boys and 1.5 cm larger for Inuit girls.
Using the WHO growth curves to observe the Inuit cohort led to significant overdiagnosis of macrocephaly and underdiagnosis of microcephaly, the researchers concluded. Using Inuit-specific percentiles, however, 25%-30% fewer boys and 15%-20% fewer girls had macrocephaly diagnoses, meaning that 651 fewer children would have macrocephaly diagnoses. Around 2% more children would be considered microcephalic, which was 79 more children than indicated by the WHO growth curves.
“Our research team fully anticipated that we would find larger head circumferences, though it was surprising to learn just how prevalent ‘macrocephaly’ is in otherwise neurologically healthy Inuit children,” said Joyal.
New Charts Coming 
Previous studies have found that standardized growth charts may not reflect local populations, including Indigenous groups in Canada and other countries, such as Cree children in Quebec, Inuit children in Greenland, and other native populations in Australia, Japan, and Turkey.
Joyal and colleagues now plan to work with local Inuit partners in Nunavut to create population-specific head circumference growth charts that can be used along with the WHO head circumference chart to help with clinical decisions, she said.
“This [work] would have implications for Inuit children throughout Canada and the world — and possibly other Indigenous children in Canada,” Joyal said.
Working with local communities is key, she noted, pointing to the partnerships with Nunavut Tunngavik, Qaujigiartiit Health Research Centre, and Government of Nunavut Department of Health for data analysis and clinical collaborations.
“Health-related research is best carried out in partnership with Indigenous people to ensure that the balance of harms and benefits is fully considered throughout the process,” said Sorcha Collins, a public health researcher at The University of British Columbia in Vancouver, British Columbia, Canada, who has studied child-maternal health and medical genetics among Inuit children in Nunavut.
“Research in Indigenous communities may inadvertently cause harm by creating stigma for those with a described risk,” she said. “However, there is also harm in avoiding research that may provide insights into health disparities.”
The study was funded by a grant from the Canadian Institutes of Health Research Partnerships for Health System Improvement program and by the Government of Nunavut. Joyal and Collins reported no relevant financial relationships.
Carolyn Crist is a health and medical journalist who reports on the latest studies for Medscape Medical News, MDedge, and WebMD.
 
Send comments and news tips to [email protected].