I too have MMN, and I wish the doctor had answered your question. I worry about my child too.
Thank you for your question. Although without being able to examine you I can not offer you the specific advice on diagnosis and treatment that you need, but I would try to provide you some relevant information about your health concern.
With multifocal motor neuropathy (MMN) there are symptoms of progressive weakness, muscle wasting, and muscle fasciculations, spasticity. In this disease, motor neurons are affected mainly that may affect all voluntary motions. Investigations such as blood tests, EMG/MRI, genetic reasons are extremely important in order to know its progression. Usually, there is no permanent cure but effective rehabilitation program would surely help in providing relief in your symptoms. Hope this helps.