Intraepidermal nerve fiber density at the distal leg: a worldwide normative reference study

TLDR

Skin biopsy for small‑fiber neuropathy requires normative reference values to ensure diagnostic reliability. The study aimed to determine age‑stratified normative values for intraepidermal nerve fiber density at the distal leg. Data from 550 healthy adults across eight international laboratories were pooled using a standardized 3‑mm biopsy protocol and quantile regression, with BMI, height, and weight examined for influence. IENF density decreased significantly with age in both sexes, while height, weight, and BMI had no effect, providing new normative reference values for clinical use.

Abstract

The diagnostic reliability of skin biopsy in small fiber neuropathy depends on the availability of normative reference values. We performed a multicenter study to assess the normative values of intraepidermal nerve fiber (IENF) density at distal leg stratified by age deciles. Eight skin biopsy laboratories from Europe, USA, and Asia submitted eligible data. Inclusion criteria of raw data were healthy subjects 18 years or older; known age and gender; 3-mm skin biopsy performed 10-cm above the lateral malleolus; bright-field immunohistochemistry protocol, and quantification of linear IENF density in three 50-µm sections according to published guidelines. Data on height and weight were recorded, and body mass index (BMI) was calculated in subjects with both available data. Normative IENF density reference values were calculated through quantile regression analysis; influence of height, weight, or BMI was determined by regression analyses. IENF densities from 550 participants (285 women, 265 men) were pooled. We found a significant age-dependent decrease of IENF density in both genders (women p < 0.001; men p = 0.002). Height, weight, or BMI did not influence the calculated 5th percentile IENF normative densities in both genders. Our study provides IENF density normative reference values at the distal leg to be used in clinical practice.