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It is very unlikely these are seizures, especially infantile spasms. Head shaking is often a behavioral issue, as the neurologists have suggested. If they were seizures you would not be able to stop them by getting his attention. Kids with infantile spasms start regressing developmentally when the spasms begin.
Another possibility is something called spasms nutans, which can show up around this time, but is associated with a head tilt and shaking of the eyes, called nystagmus. I would assume at least one of the two neurologists would have picked this up if it were present. Spasms nutans and other behaviors often go away over time and are typically benign. As long as he is developing normal there isn't much to worry about.
Behaviors can occur very frequently throughout the day. If they were seizures, the more he would do it, the more "out of it" he would get since the brain starts shutting down to recuperate after seizures. So, if he is doing it quiet a bit, the most likely diagnosis is behavioral, but he should be evaluated for spasms nutans as I mention above. This is a benign condition which he will grow out of any way. It is a very good sign that he is making normal development with such frequent episodes since it shows that it is not something bad.
Please let me know if you have any other questions.
I really don't think you have anything to worry about. Development is the best sign of how good or bad something is behaviorally. I will assume the EEG will be normal, but an easy test to get to help you feel assured as well.
Please let me know if there is anything else I can answer for you.
Given that he would need anesthesia to get a good scan, and many things can be missed on an MRI scan between 6 months and 18 months, due to the water content of the brain, if he is doing well developmentally and the EEG is normal, I would hold off on getting the MRI scan. If anything changes you can always get one. If there weren't the risk of anesthesia attached to getting one, I would be all for it since it is benign, as far as we know.
Typically kids grow out of these behaviors between the ages of 1 and 2 years, but some have gone on as long as through age 3. I can definitely appreciate your concern since my daughter used to bring her hands up in fists, shake them and screech for apparently no reason. Since she was doing so well developmentally, I watched her and she grew out of that behavior around a year of age. It seems like a long way to wait, but believe me, it will be here before you know it!
Typically EEGs are read the day they are done or the day after. If there is something abnormal on an EEG, the person reading it usually calls the referring doctor that day.
The spinning fan issue can be one of two things. First, the spinning sets off a normal response called optokinetic nystagmus. It's yours eyes constantly refocusing on a blade as it goes around. You can even see some adults bob their head while looking at a fan. Another possibility is these spells are seizures that are set off by flashing lights (photic induced seizures). These are extremely rare, but will be picked up the EEG assuming they flashed a strobe light in his eyes during the EEG.
I am happy to keep answering questions for you, but would ask that you accept my answer.