Sickle cell disease (SCD) -related neurological complications include overt stroke, silent infarctions and cognitive impairment (CI). CI significantly impacts developmental growth and quality of life. Despite the high prevalence of SCD in sub-Saharan Africa, there is limited information on the burden of neurological dysfunction. To address this gap, we conducted a study to elucidate the prevalence and correlates of CI in SCD-children in an urban tertiary care setting in Nigeria.
This case-control, cross-sectional study was approved by the University of Pittsburgh IRB, Lagos University Teaching Hospital (LUTH) and Lagos State University Teaching Hospital (LASUTH) in Nigeria. Participants were recruited from the LUTH sickle cell clinic and the Sickle Cell Foundation-associated clinics, which included a transcranial Doppler (TCD) clinic. Participants were English-speaking children between the ages 6-16 with laboratory-diagnosed homozygous SCD (HbSS, sickle cell anemia). Children who had an on-going sickle cell crisis or who received a blood transfusion within 3 months were excluded from the study. HbAA siblings of the patients and unaffected age-matched children from the LASUTH pediatric primary care clinic were recruited as control subjects. For a comprehensive assessment of cognitive function, subtests of the Wechsler Intelligence Scale for Children (WISC IV) were administered to assess processing speed (Symbol Search, Coding subtests) and Working Memory (Digit Span, Symbol search subtests) indices. Baseline hemoglobin levels were obtained via a Stat-site hemoglobin analyzer, and oxygen saturation levels were obtained using a pulse oximeter. Baseline demographic data was obtained by surveying the parents/guardians. Lastly, children recruited from the Sickle Cell Foundation TCD clinic (n=24) were stratified by stroke risk levels (standard, conditional, high and indeterminate) based on the TCD velocity values.
A total of 56 children diagnosed with sickle cell disease (M=29, mean age=9.2, SD: 2.76) and 42 unaffected children (M=24, mean age= 9.41, SD: 2.75) participated in this study. We found a higher prevalence of cognitive deficits, especially in areas of processing speed (p=0.013) and short-term auditory memory (p=0.002) in SCD patients as compared to controls. There was also a close association with working memory deficits (p=0.07). Surprisingly, we did not find an association between the cognitive performance of SCD children and their levels of anemia, oxygen levels or body mass index. TCD high risk level was marginally associated with a lower hemoglobin and severe anemia (p=0.05) although there was no significant correlation with working memory and processing speed indices.
Children with SCD in Nigeria suffer from cognitive deficits in the areas of memory and attention when evaluated with subtests of the Wechsler Intelligence Scale for Children. We found that, unlike other studies of cognitive function in SCD, our study did not find a correlation between cognitive function and hemoglobin level. It is, therefore, possible that other local environmental or disease-specific factors may be associated with CI in our SCD cohort, or that anemia may affect other cognitive domains not explored by our research. Larger, longitudinal studies should be performed to further elucidate the cognitive function of pediatric SCD patients in Nigeria so that appropriate, locally targeted, preventive interventions can be developed.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.