Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
There are 2 types of nerves that provide sensation to the feet, large nerves and small nerves. A problem with either of these could lead to burning and tingling. There are many many causes to this group of disorders called "neuropathies". They include but are not limited to most commonly diabetes, vitamin deficiencies, autoimmune disorders such as lupus or a disease called Sjogren's, certain types of neoplasm, and certain toxins (such as lead). Other causes could be genetic, metabolic, and hereditary disorders, and what tests need to be ordered depend on the history and physical examination of the patient. With small fiber neuropathy, the EMG/NCS test which measures how nerves conduct electricity and how muscles respond to them may be normal (as you mentioned). In large fiber neuropathy, it will be abnormal. Small fiber neuropathy can be diagnosed with a skin biopsy and with a test called a QSART. These are specialized tests performed at a limited number of centers. Treatment typically includes neuropathic medicines such as gabapentin or pregabalin.
If you continue to have a non-diagnostic workup, you may need to be referred to a large academic medical center with a neuromuscular center.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
I wanted to follow-up with my diagnosis. All of my lab tests that were looking for autoimmune disease or early signs of cancer came back negative. My diagnosis is "idiopathic generalized small fiber ganglionopathy". The paresthesia covers 100% of my skin including my face, scalp, inside my mouth and my tongue. So far I have tried Gabapentin, Lyrica, Cymbalta and Tramadol for relief but nothing has helped. The next step will be an attempt to merge a tricyclic antidepressant with my current antidepressant regimen which is based on Prozac. This really *****...
Thank you. I received my biopsy results yesterday which confirmed that I do have small fiber neuropathy. My Dr is sending me a lab request to dig much deeper into possible causes. In the mean time the spread of the paresthesia is complete and more severe. I am fortunate to be linked with a large academic medical center and am hopeful that they can find out what is behind this before it becomes more debilitating. They still seem somewhat baffled by the very atypical way my case has evolved. Thank you for listening.