[Early diagnosis of painful diabetic neuropathy by corneal confocal microscopy]

To explore the early diagnosis of painful diabetic neuropathy by observing the alterations in corneal innervation with corneal confocal microscopy.

Fifty aged-matched control subjects, 45 diabetic neuropathy including 20 subjects with type 2 diabetes and painful neuropathy (PDN) and 25 subjects with type 2 diabetes and painless neuropathy (PLN) underwent detailed evaluations of their neuropathic symptoms. The examinations of visual analogue scale (VAS), contact heat evoked potential (CHEP) and corneal confocal microscopy (CCM) were employed to quantify small nerve fiber pathology and their degree of pain. We evaluated the use of a novel in vivo technique CCM in assessing painful neuropathy compared to CHEP.

The results of CHEP and CCM were significantly different in the diabetic groups compared to controls. T test indicated patients with PDN had significant reductions in corneal nerve fiber length (NFL), nerve branch density (NBD), nerve fiber density (NFD) and increased corneal nerve fiber tortuosity (NFT) (13 ± 4 vs 11 ± 3, 62 ± 24 vs 47 ± 19, 32 ± 13 vs 22 ± 8, 2.8 ± 0.9 vs 3.2 ± 0. 8; t = 40.43, 27.27, 42.21, 194.39, P = 0.039, 0.011, 0.017, 0.006), (t = 40.43, 27.27, 42.21, 194.39, P = 0.039, 0.011, 0.017, 0.006). Pearson's correlation analysis showed pain severity correlated significantly with cornea nerves damage. VAS correlated significantly with NFL, NBD, NFD and NFT (r = 0.782, -0.376, -0.504, all P < 0.001).

CCM provides a sensitive and noninvasive modality of detecting small nerve fiber damage in patients with PFN. And these abnormalities may be a sensitive predictor for the presence of pain in diabetic neuropathy patients.