Corneal nerve loss is related to the severity of painful diabetic neuropathy.

Overview

abstract

BACKGROUND AND AIM: Previously we have shown that patients with painful diabetic neuropathy have greater corneal nerve loss compared to patients with painless diabetic neuropathy. This study investigated if the severity of corneal nerve loss was related to the severity of painful diabetic neuropathy (PDN). METHODS: Participants with diabetic neuropathy (n=118) and healthy controls (n=38) underwent clinical and neurological evaluation, quantitative sensory testing, nerve conduction testing and corneal confocal microscopy (CCM) and were categorized into those with no (n=43), mild (n=34) and moderate-to-severe (n=41) neuropathic pain. RESULTS: Corneal nerve fibre density (P=0.003), corneal nerve fibre length (P<0.0001) and cold perception threshold (P<0.0001) were lower and warm perception threshold was higher (P=0.002) in patients with more severe pain, but there was no significant difference in the neuropathy disability score (P=0.5), vibration perception threshold (P=0.5), sural nerve conduction velocity (P=0.3) and amplitude (P=0.7), corneal nerve branch density (P=0.06) and deep breathing-heart rate variability (P=0.08) between patients with differing severity of painful diabetic neuropathy. VAS correlated significantly with CNFD (r= -0.3, P=0.0002), CNBD (r= -0.3, P=0.001) and CNFL (r= -0.4, P<0.0001). Receiver operating curve (ROC) analysis showed that CNFD had an area under the curve (AUC) of 0.78 with a sensitivity of 0.73 and specificity of 0.72 for the diagnosis of painful diabetic neuropathy. CONCLUSIONS: Corneal confocal microscopy reveals increasing corneal nerve fibre loss with increasing severity of neuropathic pain and a good diagnostic outcome for identifying patients with painful diabetic neuropathy.