Why does paresthesia progress in post-polio syndrome?

Hi doctor,

The patient is a 50 year old woman with a history of polio in childhood and complains of paresthesia since a year. It started suddenly from the toes on both sides and it progressed to upper back (T4) in 20 days. She was hospitalized with post-polio syndrome and treated with intravenous immunoglobulin (IV Ig). She complained of bilateral tinnitus and seeing some flash of light in central vision after IV Ig therapy. She had paresthesia of fingers and both hands after two months. She was hospitalized again and treated. She lost left leg movement during hospitalization, which progressed to hemiplegia. She denies any trauma, fever or incontinence. Her medication includes Gabapentin, Vitamin D and B1, Duloxetine and Chlordiazepoxide. Past medical history includes polio and migraine. Family history includes father with Alzheimer's, mother with hypertension (HTN) and heart failure. She is married, monogamous with husband and adopted one child. On physical examination, pupil was normal and no nystagmus. Laboratory tests showed complete blood count (CBC) and differential nil, erythrocyte sedimentation rate (ESR) 40, CRP 25. Also, I have attached her magnetic resonance imaging (MRI) report.