How often do you order imaging to assess for possible degenerative joint disease in the spine in patients with neuropathic itch?  

Only if the itch is localized, mainly unilateral like in notalgia paresthetica of the back or the forearm.

I agree with Dr. @Aida Lugo-Somolinos and will add that there is also a higher yield of spinal imaging in chronic anogenital pruritus. I personally find imaging quite unsatisfying because regardless of what you find the treatment algorithm is basically the same. However, theoretically as a last-line...