Peripheral cholinergic function in humans with chronic fatigue syndrome, Gulf War syndrome and with illness following organophosphate exposure
Acetylcholine abnormalities are particularly implicated in people such as Gulf War veterans and agricultural workers, who have been exposed to substances which inhibit the activity of the enzyme cholinesterase. These people suffer from symptoms which can be very similar to those of ME/CFS, although there are important differences.
The acetylcholine blood flow responses of a group of these people were compared with the responses of ME/CFS patients, to see whether they have the same abnormalities. However, the Gulf War veterans and agricultural workers all tended to have a normal response to acetylcholine, suggesting that their illnesses are fundamentally different to ME/CFS. This is interesting considering that patients from all of these groups are often collected together under the term "chronic fatigue syndrome".
Methacholine is a chemical which is almost identical, and has similar effects, to acetylcholine, except that it is much less sensitive to the action of cholinesterase. For this reason, the blood flow response to methacholine is normally higher than that to acetylcholine. However, in patients with ME/CFS, they were similar; further evidence of a cholinesterase abnormality.