I have been suffering with idiopathic small and large fiber neuropathy for 4 years. I personally have been worked up and tested by 4 different and capable neurologists. Had every test possible.
Every person with this condition is a little different. I have been on zneurontin - Lyrica - Vimpat - Trilipal, all for a significant amount of time. None of them helped my pain.

On the positive note, I suggest that your husband see at least one neurologist and follow directions. He must try everything possible to get the correct diagnosis. Keep active as much as possible.