Infantile spasms represent an age-dependent epileptic syndrome that usually begins between 4 and 6 months of life; onset is before the age of 12 months in about 90% of cases. The spasms are characterized by symmetric, bilateral, brief, and sudden contractions of the flexor or extensor muscle groups. The seizures may be resistant to treatment, and the syndrome frequently is associated with mental retardation.
In 14% to 38% of cases, infantile spasms are "cryptogenic," without identifiable underlying cause. However, the majority of patients have so-called "symptomatic" infantile spasms, with some identifiable pre-, peri-, or postnatal factor that underlies the syndrome: hypoxemiaischemia, intrauterine infection, a cerebral malformation or degenerative disorder, tuberous sclerosis, a genetic abnormality, an inborn error of metabolism, an intracranial hemorrhage, traumatic delivery, head injury, or a central nervous system infection.