Congenital Myasthenic Syndromes (CMS)
The cholinesterase inhibitors used to treat myasthenia gravis (MG) are helpful in some types of congenital myasthenic syndromes (CMS) but may be harmful in others. See below for more.
It’s important to realize that since CMS isn’t an autoimmune disease, it doesn’t respond to immunosuppressant drugs or other treatments aimed at the immune system.
These drugs, also known as anticholinesterases, have been used against MG since the early 1990s and can produce relief from symptoms within minutes. The one most commonly used is pyridostigmine (Mestinon).
Cholinesterase inhibitors boost levels of ACh — a chemical necessary for proper muscle function — not only at the neuromuscular junction, but also in the autonomic nervous system (which controls involuntary bodily functions). Sometimes the drugs can cause diarrhea, abdominal cramps and/or excessive saliva. To minimize these side effects, the physician might lower the dose of cholinesterase inhibitors or prescribe atropine, which blocks the ACh receptors on nerve cells.
The types of CMS that respond to cholinesterase inhibitors include:
- Presynaptic CMS
- Postsynaptic CMS (ACh receptor deficiency, fast-channel CMS) — In addition to cholinesterase inhibitors, this type is also treated with 3,4-DAP, a drug that enhances ACh release.
Types of CMS that do not respond to cholinesterase inhibitors include:
- Postsynaptic CMS (slow-channel CMS) — This type is treated with quinidine or fluoxetine, both of which plug the ACh receptor.
- Synaptic CMS — There currently are no drug treatments for this type of CMS.