Intraepidermal nerve fiber density and its application in sarcoidosis

BACKGROUND: Intraepidermal nerve fiber density (IENFD) is considered a good diagnostic tool for small fiber neuropathy (SFN). OBJECTIVES: To assess stratified normative values for IENFD and determine the reliability and validity of IENFD in sarcoidosis. METHODS: IENFD was assessed in 188 healthy volunteers and 72 patients with sarcoidosis (n = 58 with SFN symptoms, n = 14 without SFN symptoms). Healthy controls were stratified (for age and sex), resulting in 6 age groups (20-29, 30-39, ... up to '70 years) containing at least 15 men and 15 women. A skin biopsy was taken in each participant 10 cm above the lateral malleolus and analyzed in accordance with the international guidelines using bright-field microscopy. Interobserver/intraobserver reliability of IENFD was examined. In the patients, a symptoms inventory questionnaire (SIQ; assessing SFN symptoms) and the Vickrey Peripheral Neuropathy Quality-of-Life Instrument-97 (PNQoL-97) were assessed to examine the discriminative ability of normative IENFD values. RESULTS:: There was a significant age-dependent decrease of IENFD values in healthy controls, with lower densities in men compared with women. Good interobserver/intraobserver reliability scores were obtained (κ values '0.90). A total of 21 patients with sarcoidosis had a reduced IENFD score (<5th percentile; 19 [32.8%] in patients with SFN symptoms, 2 [14.3%] in patients without SFN symptoms). The validity of the normative IENFD values was demonstrated by distinguishing between the SIQ scores and various PNQoL-97 values for the different patient groups. CONCLUSION: This study provides clinically applicable distal intraepidermal nerve fiber density normative values, showing age-and sex-related differences.