Abstracts

RATIONALE: Subcortical band heterotopia (SBH) is a disorder of neuronal migration that is associated with epilepsy and cognitive impairment. This condition is genetically related to lissencephaly and results from mutations of the doublecortin gene. Although it is known that patients with SBH display varying degrees of intellectual impairment, little is known about the pattern of spared and affected cognitive functions associated with this condition. We present a series of four patients with SBH who display intellectual deficits, but relatively intact memory abilities. This pattern of cognitive abilities has not been previously reported in individuals with SBH and is highly unique amongst individuals with focal epilepsy who characteristically display memory deficits. At the end of this activity the participants should be able to discuss the cognitive profile associated with subcortical band heterotopia.
METHODS: Clinical interviews and neuropsychological assessments of four patients (age 10-32 years) with SBH were conducted. Each patient was classified with SBH based on MRI evidence.
RESULTS: All four patients displayed deficits in overall intelligence, ranging from moderate mental retardation to the borderline level (IQ range: 44-77). Analysis of the pattern of performance of each patient across cognitive domains indicated a highly consistent pattern of impairment in processing speed, attention, language, and visuomotor abilities. By contrast, memory performance was a relative strength and clearly exceeded expectations based on intelligence and adaptive functioning. Table 1 presents a summary of the neuropsychological test findings.
CONCLUSIONS: The most notable neuropsychological finding in these four patients with SBH was of relatively preserved memory abilities in the context of intellectual impairment. This cognitive profile is highly unique amongst individuals with focal epilepsy and is suggestive of intact functioning of the mesial temporal areas in this condition. These findings are supported by radiological and pathological evidence in the literature of spared mesial temporal structures in SBH. Understanding the cognitive strengths and weaknesses of patients with SBH is necessary to assist them in obtaining optimal educational services and achieving maximal independence. Future research with larger groups of patients is required to determine whether this pattern of spared and impaired cognitive functions is related to features of the heterotopic band or the degree of cortical abnormality.[table1]