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Infantile spasms: II. Lenticular nuclei and brain stem activation on positron emission tomography
H T Chugani1, D A Shewmon, R Sankar
1Department of Neurology, University of California, Los Angeles, School of Medicine 90024.
Insights
Infantile spasms, a type of infant seizure, show increased glucose metabolism in the brain's lenticular nuclei. This finding suggests the lenticular nuclei play a role in the development of these generalized seizures.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Pediatric Neurology
Background:
- Infantile spasms are generalized seizures occurring in early infancy.
- They are thought to arise from complex interactions between cortical and subcortical brain regions during development.
Purpose of the Study:
- To investigate the neuroanatomical substrates underlying infantile spasms.
- To determine local cerebral metabolic rates for glucose (1CMRG1c) in infants with spasms using PET.
Main Methods:
- Positron emission tomography (PET) was used to measure 1CMRG1c in 44 infants with spasms.
- Infants were studied awake with continuous electroencephalographic monitoring.
- Results were compared to age-matched normal infants.
Main Results:
- A symmetrical increase in 1CMRG1c in the lenticular nuclei was observed in 32 out of 44 infants.
- This hypermetabolism was independent of spasm etiology (cryptogenic or symptomatic).
- Associated cortical abnormalities included hypometabolism (22 infants) or hypermetabolism (5 infants).
Conclusions:
- The lenticular nuclei may contribute to the pathophysiology of infantile spasms.
- Findings support the symmetrical clinical presentation of spasms, even with focal cortical lesions.
- A proposed neuronal circuitry model for spasm generation is presented.
Abstract:
Infantile spasms are generalized seizures specific to early infancy, and are believed to result from complex cortical-subcortical interactions during a critical period of development. We used positron emission tomography (PET) to determine local cerebral metabolic rates for glucose (1CMRG1c) in 44 infants with spasms, in an attempt to define the neuroanatomical substrates that mediate these seizures. All infants were studied in the awake state during continuous electroencephalographic monitoring. The most consistent abnormality on PET, seen in 32 infants, was the symmetrical increase in 1CMRG1c in the lenticular nuclei, compared to age-matched normal infants (p less than 0.05). In 21 infants, even though the brain stem appeared to be visually more prominent compared to normal infants, statistically significant differences could not be demonstrated. Relative hypermetabolism of the lenticular nuclei (1) occurred irrespective of whether the spasms were cryptogenic or symptomatic, (2) was associated with focal cortical hypometabolism in 22 and focal cortical hypermetabolism in 5 of the 44 infants, and (3) was not characterized by any specific electroencephalographic abnormality during PET. These findings suggest that the lenticular nuclei may contribute to the pathophysiological state that predisposes to infantile spasms, and is consistent with the observation that spasms are clinically symmetrical even when focal cortical lesions are present. A scheme describing the neuronal circuitry likely to be involved in the generation of infantile spasms is proposed.