I can't put my finger on the other article I recently saw (other than yours), but here's the Gov't NIH starting clinical trials for IVIG for idiopathic SFN....because many doctors (mine included from Johns Hopkins) think there still may be an immunological element, even in idiopathic. They would not be doing this study if there wasn't a question of it possibly working.

Intravenous Immunoglobulin Therapy for Small Fiber Neuropathy - Full Text View - ClinicalTrials.gov