Your symptoms can be due to polyneuropathy. Following are the causes of polyneuropathy (many times cause it is not known);
2) An underactive thyroid gland
4) Thiamine deficiency
5) Vitamin B 12 deficiency (pernicious anemia)
6) Vitamin B 6 (pyridoxine) taken in excessive amounts
7) Drugs, medications, herbs
8) Autoimmune diseases
9) Heavy metals such as lead and mercury.
Following investigations are done (many of which had been done for you);
1) Electromyography/nerve conduction studies (EMG/NCS)
2) MRI of the spine and brain
3) blood glucose and glycosylated hemoglobin
4) serum B12 level with methylmalonic acid (with or without homocysteine),
5) serum protein electrophoresis
6) Anti-nuclear antibody
7) Lyme testing
8) Rheumatoid factor
9) Sjogren's syndrome testing (Anti-Ro, Anti-La Antibodies)
Skin and nerve biopsy may be needed / recommended after the results of these investigations
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.