Gabopentin for horses?

Does anyone have any experience of using Gabopentin for undiagnosed pain in a horse? My horse has a severe skin condition with no external symptoms except that she mutilates herself scratching with her teeth (or on anything handy), Steroids have had zero effect so it appears that the problem is not actually in her skin. I suspect the problem is neuropathic as it is limited to specific parts of her back. Has anyone any experience of using Gabopentinn or can suggest any other possible remedy? This has been proven to NOT be an allergy but the vet has no idea what it is.