Since you mentioned "intense dryness of the sinuses", I'm curious if you have dry eyes or mouth? Sjogren's is an autoimmune disease that is not only common to include neuropathy, but 40% of patients have negative blood work. Have they run SSA & SSB for Sjogren's? If you have dry eyes or mouth, I would request they run these labs. If they are negative, then you might request a lip biopsy.

Also, did they diagnose neuropathy just from temperature & tuning fork? Did they do a skin biopsy for small fiber neuropathy? If not, it might be worth asking for.

BTW, iron deficiency anemia is also common with autoimmune disease. There are options to increase ferritin if supplements are not working. One is Ferrlecit (iron) by IV...if your doctor thinks it's bad enough. Do you know your ferritin level?