Brief Answer:
Can be ibs.
A diagnosis of exclusion.

Detailed Answer:
Hello,
Thanks for choosing HealthcareMagic for your query .
Have seen your details and i appreciate your concerns.
I can very well understand the level of frustration you must be having and i have my heart felt sympathy with the young kid but we humans don't have any thing in our hand except trying.

I hope that my answer would help you and would provide you with some basic informations which could help you understand things better,

First and the foremost thing which came to my mind after going through your
narration is irritable bowel disease or its variant but before that i have some questions as it is a complex case therefore a detailed history along with investigation plus response to medications would play a significant role.

1)My 40 year old son has debilitating stomach issues -What exactly are his symptoms
Does he have symptoms of unformed stools or have bloating ,constipation or diarrhea. Are they occasional or for a long period of time.
What were the medication tried on him?what was the doses of medications given?
Name the medicines and the duration for which they were given?
Mark response to medicine on a scale of 0-10.

As you have written that every type of test was normal i would consider that along with his his Colonoscopy and Upper gi endoscopy,Sigmoid endoscopy,MRI abdomen and PET abdomen has already been done.Ok!

Now let me sum up what i think it could be.
History is highly suggestive of IBS. In IBS there is some problem in the functional ability of the gut that leads to the symptoms of irritable bowel syndrome. The structure of the intestines is normal, only functional abnormality occurs in this condition.So frankly speaking (IBS) represents a functional disorder of gastrointestinal tract without the presence of an anatomic defect.As structure of gut and intestines are normal all the tests performed would turn up normal.Therefore doctor would say that all tests are normal however despite of this fact the patient would be symptomatic and sometimes even to level of debiliation.

Now the problem in treating such patient is that as we don't know the exact cause of problem we can never say which medicine would be effective on that particular patient.Recent studies by French scientists have indicated that the most important mechanisms including this mystery disease is visceral sensitivity, abnormal gut motility and autonomous nervous system dysfunction. The interactions between these three mechanisms make bowel's function susceptible to many exogenous and endogenous factors like gastrointestinal flora, feeding and psychosocial factors.
In easy language either intestines are not working properly or brain is not controlling intestines properly by using its regulators termed as hormones or there is a possibility that nerve supply to intestine is tempered.

Recently there are papers about the influence of genetic factors and polymorphisms of human DNA in the development of IBS is equally important.So it could also be related to genes and DNA.

The million dollar question is how to repair a system when you don't know which part of it is faulty.Some patients have symptoms of unformed stools some have bloating and some may have severe constipation. Some patients have occasional symptoms whereas others may have symptoms for a long period of time.So as seen above every patient is different.Intensity of symptoms in every patient is different as so is the response to medicines and life style change.A patient may respond good to one medication while other patient is totally unresponsive to the same.

Before moving to any other details i would like you to revert back with answers my question.

Hope i was a bit helpful to you.
Waiting for your answers.Please do specify name of all medications doses done on him.

Warm regards.

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Brief Answer:
follow up.

Detailed Answer:
Hi again,
Please take your time and give a elaborate presentation of this case.
As i can't physically examine him all i depend on is the history provided by you.

Waiting.

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