The relation of infantile spasms, tubers, and intelligence in tuberous sclerosis complex

Abstract

Background: The aetiology of the learning difficulty in tuberous sclerosis is debated. It may be related to the amount of tubers in the brain or caused by the infantile spasms that occur in early life.

Aims: To examine the relative contributions to final intelligence (IQ) made by both cerebral tubers and infantile spasms.

Methods: As part of an epidemiological study of tuberous sclerosis in the south of England, patients were recruited who were able to undergo magnetic resonance imaging (MRI) without the need for an anaesthetic. Epilepsy history was determined by interview and review of clinical records. IQ was assessed using either Wechsler intelligence scales or Raven's matrices.

Results: A total of 41 patients consented to have an MRI scan. IQ scores were normally distributed about a mean of 91. Twenty six patients had a positive history of epilepsy, and 11 had suffered from infantile spasms. There was a significant relation between the number of tubers and IQ. Infantile spasm status partly confounded the relation between tubers and IQ, but did not render the relation statistically insignificant. The relation between infantile spasms and learning difficulty remained strong even when controlling for the number of tubers.

Figure 1

Scatter plot of intelligence quotient scores versus total number of tubers identified on MRI scan. Patients with a negative history of infantile spasms are depicted by a triangle and those with a positive history by a circle. Two regression lines are drawn depicting the linear relation between intelligence quotient and tuber count both with (solid line) and without (dashed line) a positive history of infantile spasms.