Ratio of Distal to Proximal Epidermal Nerve Fiber Density in Small Fiber Neuropathy
Georgette Dib1, Matthew Varon3, Omar Jawdat4, Constantine Farmakidis2, Swathy Chandrashekhar3, Jeffrey Statland3, Mazen Dimachkie3, Mamatha Pasnoor3
1Neurology, KUMC, 2KUMC, 3University of Kansas Medical Center, 4The University of Kansas Medical Center
Objective:
To assess the distal-to-proximal IENFD ratio in patients with SFN.
Background:
IENFD assessment has become an important tool for diagnosis of small fiber neuropathy (SFN). Distal leg, distal thigh and proximal thigh are the usual sites of biopsy. At least two-site biopsies are performed to assess for length dependency. Age dependent normative data have been established for distal leg. In some patients with paresthesia, although the distal and proximal biopsies are normal, the distal IENFD is much less compared to proximal density. There is limited literature looking at the significance of the ratio of distal-to-proximal biopsy IENFD.
Design/Methods:
After IRB approval, we retrospectively evaluated charts of subjects who underwent skin biopsy for evaluation of SFN from May 2020 to May 2023 in the neurology department of KUMC. The distal leg, proximal thigh IENFD information was collected, and ratio calculated for all subjects. Subjects were categorized as having possible or probable SFN based on the clinical criteria established by Diabetic Neuropathy Study Group of the European Association for the Study of Diabetes (NEURODIAB). Descriptive and correlation analysis was performed.
Results:
Total of 56 charts were reviewed. Female to male ratio was 3:1. Mean age was 50±26. Total number of patients with clinical diagnosis of neuropathy (probable and possible) was 46. IENFD was abnormal in 23, normal in 23 with mean distal to proximal ratio of 0.5 and 0.6 respectively. The mean ratio for patients without clinical diagnosis of neuropathy was 0.9. The 23 patients with clinical diagnosis of neuropathy with negative skin biopsy had significant difference in mean ratio compared to patients without clinical diagnosis of neuropathy using T-test (p 0.02).
Conclusions:
The findings of this study suggest that in patients with normal IENFD and clinical suspicion for SFN, the distal-to-proximal ratio may provide additional benefit in making the diagnosis.