Congenital myastenic syndrome (CMS)

Diagnosis 

If such symptoms are present, consult a neurologist. They will ask questions and perform a physical exam to assess the extent of weakness. To check for increased weakness with exertion, patients may be asked to perform tasks like sustaining an upward gaze, holding out their arms, or climbing steps. 

• Blood test: To check for Myasthenia Gravis (MG), a blood test can detect antibodies to the ACh receptor. A negative result can suggest CMS, but not always. 
• Electrodiagnostic testing: Electrodes are used to measure muscle electrical signals. Surface electrodes deliver small nerve shocks, and others record muscle responses. This helps assess muscle function. 
• Edrophonium test: In some cases, the neurologist may administer an intravenous injection of edrophonium. A temporary strength increase following this test is indicative of CMS. 
• Family history: While a family history of myasthenic symptoms supports a CMS diagnosis, it’s not always present. Genetic and muscle tissue tests may be required for some CMS types to provide a definitive diagnosis. 
• Genetic test: In cases where a conclusive genetic diagnosis is needed, further testing may be required. 

Treatment   

Cholinesterase inhibitors, which are commonly used to manage myasthenia gravis (MG), offer benefits in specific cases of congenital myasthenic syndrome (CMS) but can pose risks in others. It’s crucial to understand that CMS, unlike autoimmune conditions, does not react to therapies targeting the immune system, such as immunosuppressant drugs. 

Cholinesterase Inhibitors: 

Anticholinesterase drugs, also called cholinesterase inhibitors, have been used to treat myasthenia gravis (MG). They provide rapid relief from symptoms, with pyridostigmine (Mestinon) being the most common option. 

These drugs increase acetylcholine (ACh) levels, a crucial chemical for proper muscle function, not only at the neuromuscular junction but also in the autonomic nervous system, which controls involuntary bodily functions. Occasionally, they can cause diarrhea, abdominal cramps, or excessive saliva. To mitigate these side effects, the doctor may lower the dose or prescribe atropine, which blocks ACh receptors on nerve cells. 

Cholinesterase inhibitors are effective for: 

• Presynaptic CMS 
• Postsynaptic CMS with ACh receptor deficiency (fast–channel CMS). In addition to cholinesterase inhibitors, amifampridine–containing drugs are used to enhance ACh release. 

Cholinesterase inhibitors do not work for: 

• Postsynaptic CMS with slow–channel CMS. Quinidine or fluoxetine is used to block ACh receptors.
• Synaptic CMS. Unfortunately, there are currently no drug treatments available for this type of CMS.