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

Aims: To assess the utility of corneal confocal microscopy in identifying small fiber damage in patients with burning mouth syndrome (BMS). Methods: 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. Results: 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. Conclusion: 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. Keywords: burning mouth syndrome, corneal confocal microscopy