Hippocampal size and memory functioning in children and adolescents with congenital hypothyroidism

Despite early diagnosis and treatment of congenital hypothyroidism (CH) after newborn screening, selective and persistent neurocognitive weaknesses may be seen. One area of particular weakness is memory, especially on tasks known to be mediated by the hippocampus. However, the hippocampus has not been directly studied in this population.

Our objective was to use magnetic resonance imaging to determine whether children and adolescents with CH have reduced hippocampal size and abnormal hippocampal growth patterns relative to peers and whether reduced hippocampal volumes in CH predict poor memory performance.

Studied were 35 CH and 44 typically developing controls aged 9-15 yr. All were assessed using standardized tests of intelligence and verbal and visual memory and received an magnetic resonance imaging scan. Parents completed a questionnaire of their everyday memory functioning (EMF). Right and left hippocampal volumes were measured by manual tracing.

CH subjects scored significantly below controls on indices of verbal but not visual memory as well as aspects of EMF. CH subjects also had smaller hippocampal volumes, particularly on the left side. Unlike controls, who showed a positive relationship between age and hippocampal volumes, age was unrelated to hippocampal size in CH. Structure-function correlations revealed significant relationships between hippocampal volumes and EMF in controls and modest correlations between hippocampal volumes and memory test scores but not EMF in CH.

Compromised hippocampal development in CH may contribute to some of the memory weaknesses observed in this population.