Hi Doster - I am sorry your son is experiencing this issue. My son has had headaches of this nature and has had a lot of reasons for them. I will try to go through the things we did.
The one significant thing that you haven't mentioned is blood pressure. Has your son had his blood pressure checked, especially during the episode of headache? Hypertension (high blood pressure) is more common in NF1. My son had headaches from about age 3 and sometimes they would make him writhe around, become pale and vomit. Panadol (which I think is similar to tylenol) and ibuprofen only partially helped. After numerous investigations - but not taking his blood pressure - we were told he had migraine syndrome and that there was nothing we could do, but try and work out what triggered it and to avoid the triggers and to give him simple analgesia when they happened. We were also told that the MRI showed severe sinusitus and so he had some treatment for this, but we didn't think that was the culprit as it made little difference. He had a mini stroke (called a trans ischaemic attack) when he was 8 or 9 and was then found to have extremely high blood pressure. He now takes blood pressure pills and is stable. These helped to resolve his frequent headaches. If you are unsure about whether his BP has been checked this would be my first action. It is quick and only makes the child's arm tingle. I would even consider hiring a machine for a week and taking his BP at diferent times of the day, writing it down and asking the doctor to review the recordings. A machine is not always the most reliable method, but it would give you a ball park and if your sons' BP was up it would give an indication of this.
We sought medical assistance at one point (I think age 6) when Nathan went straight to sleep after he vomited and seemed to twitch. He had an EEG performed which indicated epilepsy. This same thing happened a year later and again the EEG indicated epilelpsy. All up Nathan has had four of these episodes in his life and it is possible that the really bad headaches are a form of epilepsy. We opted not to medicate him for this as the episodes are so far apart and he has a bad headaches beforehand. Perhaps you could ask the neurologist if this is a possibility?
Last year Nathan had a return of headaches but these were different. These he woke up with and were associated with nausea. He had a brain tumour and hydrocephalus which developed over a three month period between MRI's. I am unclear from your post whether your son had his last MRI 5 months ago or more recently? As you can see from my post these things can develope quickly. I am also aware of a condition of the blood vessels at the base of the brain which can cause headaches and (of course) are more common in NF1. For the life of me I can't recall what its name is - some sort of syndrome. Perhaps you could google it. A test for this was included in Nathan's early investigations because he would get a bad headache when blowing up balloons and this is a sign of this syndrome. I know it sounds crazy but I am sure you want to leave no stone unturned.
Have the MRI's included a scan of his spine? As teacher 33 says the spine can influence the head and headaches. Adding a spinal MRI to the head MRI doesn't add too much time to the MRI.
I am not sure why you would pursue a gluten free diet for headaches. Is there some evidence that this will help? Nathan was gluten free from age 5 to 9 as he was thought to be coeliac / gluten intolerant (long boring story). Being gluten free did not alter his headaches in any way. I am also curious about the pain relieving meds - are they given around the clock or only at the time of a headache?
There are some other more 'natural' avenues you could consider. I wonder if it could be muscular or posture related and whether seeing a chiropractor or a cranioskeletal person would be worthwhile. I have to say up front that I am not a fan of chiropractors, but muscle tension does cause headaches. Nathan also grinds his teeth and after a bad night of teeth grinding he can wake with a headache. It causes a lot of tension in his jaw. We only found out about the tooth grinding because we all went on holiday and had to share a room for 2 nights. His grinding was unbelievable! It started about 3 in the morning or at least that's when it woke us all up!
Another consideration might be light sensitivity?
I don't know your son or your situation but I seriously doubt that a 6 year old is making up headaches and needs to see a behavioural specialist. He is missing out on the joys of childhood because he has headaches - that doesn't sound behavioural to me. Nathan has headaches many times a week and always has had. However, he can manage them himself with simple analgesia. Having his BP sorted out and then his tumour have been very helpful. He also seems to get dehydrated occassionally and this gives him a headache. We ensure he drinks 8 glasses of water a day and he does sometimes comment that this helps.
I do hope you get to the bottom of this. I think you are trying very hard to help your son and I wish you all the very best,
Una in Oz