Pathophysiology of Infantile Spasms
The spasms are generalized seizures which consist of brief muscle extension, flexion, or mixed flexion-extension jerks involving the neck, trunk, or extremities.47,49 Lateralizing or localizing clinical features may be present during the spasms.
Infantile spasms can be associated with a wide variety of neurological conditions, including metabolic, dysplastic or dysgenetic abnormalities, and various prenatal, perinatal, and postnatal insults.51 In the symptomatic category, a specific neurological condition can be identified, whereas in the cryptogenic sub-group an underlying condition is suspected based on clinical features, EEG or other tests, but a specific diagnosis cannot be made.
There is a small group (<5%) of infants with spasms, the idiopathic subgroup, which is believed not to be associated with any underlying condition. Neurodevelopment is normal at presentation, and there is a lack of focal features on clinical examination, seizure semiology or EEG. Reappearance of hypsar-rhythmia between consecutive spasms in a cluster is said to be an important feature in this subgroup.34 There is rapid response of the spasms to medical treatment and an ultimately benign course is expected. This rare situation may represent a case in which, during development, there is a chemical or physiological disturbance resulting in spasms, but which can be totally reversed with medical treatment.
With rare exceptions,38 the spasms typically begin between age 3 and 8 months and disappear by age 2 to 3 years. In other words, there appears to be a developmental window during which various brain abnormalities may result in infantile spasms as one manifestation of the underlying disorder.
Although the vast majority of brain lesions that have been identified in patients with infantile spasms involve the cerebral cortex, their locations are not specific to any cortical region.
With some exceptions, the spasms do not appear to respond to conventional anticonvulsants, but rather, to therapeutic agents not typically used in epilepsy, such as corticosteroids. If the spasms respond to such treatment, the response is often abrupt and dramatic rather than graded, as is seen in other forms of epilepsy.
KeywordsPositron Emission Tomography Partial Seizure Infantile Spasm Kynurenic Acid Lenticular Nucleus
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