Corneal Confocal Microscopy Detects Small-Fiber Neuropathy in Burning Mouth Syndrome: A Cross-Sectional Study

To assess the utility of corneal confocal microscopy in identifying small fiber damage in patients with burning mouth syndrome (BMS).

A prospective cross-sectional cohort study was conducted at two United Kingdom dental hospitals between 2014 and 2017. A total of 17 consecutive patients with idiopathic BMS aged between 18 and 85 years and 14 healthy age-matched control subjects were enrolled in this study. Corneal subbasal nerve plexus measures were quantified in images acquired using a laser-scanning in vivo corneal confocal microscope. The main outcome measures were corneal nerve fiber density, nerve branch density, nerve fiber length, and Langerhans cell density.

Of the 17 patients with BMS, 15 (88%) were women, and the mean (standard deviation) age of the sample was 61.7 (6.5) years. Of the healthy controls, 7 (50%) were women, and the mean (standard deviation) age was 59.3 (8.68) years. Corneal nerve fiber density (no./mm²) (BMS: 29.27 ± 6.22 vs controls: 36.19 ± 5.9; median difference = 6.71; 95% CI: 1.56 to 11.56; P = .007) and corneal nerve fiber length (mm/mm²) (BMS: 21.06 ± 4.77 vs controls: 25.39 ± 3.91; median difference = 4.5; 95% CI: 1.22 to 6.81; P = .007) were significantly lower in BMS patients compared to controls, and Langerhans cell density (no./mm²) (BMS: 74.04 ± 83.37 vs controls: 29.17 ± 45.14; median difference = -21.27; 95% CI: -65.35 to -2.91; P = .02) was significantly higher.

Using a rapid noninvasive ophthalmic imaging technique, this study provides further evidence for small fiber damage in BMS and has potential utility for monitoring disease progression and/or response. Furthermore, this technique shows a hitherto undocumented increased density of immune cells in this group of patients.