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MG is defined as a disease of the neuromuscular junction of striated muscle cells. Smooth muscle cells are excluded from this definition and I believe many of the digestive muscles are smooth.
One thing has been bothering me. Many smooth muscles utilize muscarinic acetylcholine receptors, versus the nicotinic acetylcholine receptors used in striated cells. If immune cells can create autoantibodies to nAChR, they sure could create autoantibodies to the muscarinic receptors mAChR. But only one lab in the world that I know of, CellTrend in Germany, specifically tests for mAchR antibodies in their POTS-CFS/ME-SFN-Long Covid test. This also raises the question whether the acetylcholine receptor antibody tests in many labs such as Mayo, LabCorp, Quest, CPL and others only detect nicotinic receptor antibodies.
Acetylcholine is a key neurotransmitter used by muscarinic receptors in the Autonomic Nervous System, which includes the digestive system, endocrine and many other parts of the body. But the ANS seems to be the orphan child among many neurologists as it’s a system, not a body part like the central nervous system, nerves and NMJ’s, partially controlled by neurotransmitters but also by hormones (which is an endocrinology thing).
I personally believe we are actually dealing with a spectrum disease of acetylcholine transmission, where MG is just a manifestation of this disease, and that an injustice is being served on patients who struggle with MG and other symptoms by restricting diagnosis and treatment to just the book definition of MG.