Follow-up Editors' Note: Intravenous Immunoglobulin Therapy in Patients With Painful Idiopathic Small Fiber Neuropathy

"Intravenous Immunoglobulin Therapy in Patients With Painful Idiopathic Small Fiber Neuropathy," by Geerts et al., compared the administration of IVIG to placebo for patients with idiopathic small fiber neuropathy (SFN) and found no significant difference in the Pain Intensity Numerical Rating Scale score. In the October 19th Editors' Note, we summarized an exchange about these findings between Wilder-Smith and Spoendlin and Faber (a coauthor on the article).(1) Wilder-Smith and Spoendlin worried that this article may inappropriately dissuade clinicians from giving IVIG to patients with autoimmune SFN. They asked the authors to (1) provide additional data on the patients who were excluded because of autoimmune disease and (2) perform subgroup analysis based on symptom duration because patients with shorter duration of symptoms may be more likely to benefit from IVIG. Faber responded that 193 of 257 (75%) patients screened for enrollment were excluded; 41 had known autoimmune conditions. Faber agreed that a randomized study on the impact of IVIG on autoimmune SFN is needed. Because 75% of patients who were screened were excluded, Wilder-Smith and Spoendlin suggested that the study population does not reflect the population of patients with SFN routinely seen in clinical practice. They also requested additional information about the excluded patients and more clinical data for all screened patients, and further underscored the potential benefit for IVIG in patients with autoimmune SFN. In response, Faber et al. provided a table detailing the explanations for exclusion and noted that their exclusion rate is on par with the median exclusion rate for randomized-controlled trials (77%). They also reiterated that their focus was on patients with idiopathic SFN, not patients with autoimmune SFN, and that their findings indicate IVIG is not beneficial for this select patient population. However, they agreed that a future randomized-controlled trial is needed to evaluate the role of IVIG in autoimmune SFN.