Abstract and Introduction
Abstract
We sought to determine whether early nerve damage may be detected by corneal confocal microscopy (CCM), skin biopsy, and neurophysiological tests in 86 recently diagnosed type 2 diabetic patients compared with 48 control subjects. CCM analysis using novel algorithms to reconstruct nerve fiber images was performed for all fibers and major nerve fibers (MNF) only. Intraepidermal nerve fiber density (IENFD) was assessed in skin specimens. Neurophysiological measures included nerve conduction studies (NCS), quantitative sensory testing (QST), and cardiovascular autonomic function tests (AFTs). Compared with control subjects, diabetic patients exhibited significantly reduced corneal nerve fiber length (CNFL-MNF), fiber density (CNFD-MNF), branch density (CNBD-MNF), connecting points (CNCP), IENFD, NCS, QST, and AFTs. CNFD-MNF and IENFD were reduced below the 2.5th percentile in 21% and 14% of the diabetic patients, respectively. However, the vast majority of patients with abnormal CNFD showed concomitantly normal IENFD and vice versa. In conclusion, CCM and skin biopsy both detect nerve fiber loss in recently diagnosed type 2 diabetes, but largely in different patients, suggesting a patchy manifestation pattern of small fiber neuropathy. Concomitant NCS impairment points to an early parallel involvement of small and large fibers, but the precise temporal sequence should be clarified in prospective studies.
Introduction
Diagnosis of diabetic sensorimotor polyneuropathy (DSPN) by clinical assessment may be variable even among proficient examiners and is less reproducible than usually assumed.[1] Therefore, objective measures to accurately determine nerve pathology are required to detect early stages of DSPN, which may be more susceptible to intervention than late-stage sequelae. Small fibers, which constitute 70–90% of peripheral nerve fibers, may be quantified in skin biopsies by assessing intraepidermal nerve fiber density (IENFD), and it has been suggested that the earliest nerve fiber damage in DSPN is to the small fibers.[2] Recently, corneal confocal microscopy (CCM), a noninvasive modality for the study of the human cornea, has emerged as a promising technique for the detection of small nerve fiber alterations.[3,4]
CCM can be used to assess the corneal subbasal nerve plexus (SNP) lying between the basal epithelium and Bowman's membrane.[5,6] Recent data suggest that CCM shows good reproducibility[7] and could be useful to document nerve regeneration after treatment intensification and simultaneous pancreas and kidney transplantation.[8,9] Previous works have also looked at its sensitivity and specificity for the diagnosis of DSPN,[10,11] including comparison with IENFD.[12] However, the vast majority of previous studies using CCM in diabetic patients have analyzed relatively small image frames of 0.15 mm2, which may not be representative of larger corneal areas.[13] As possible solutions, multiple nonoverlapping image frames per patient or larger mosaic images generated from image sequences have both been proposed.[13,14] Moreover, image assessment has been hampered by the presence of ridge-like tissue deformations in the neighborhood of the SNP and image distortions. These are induced by the anterior corneal mosaic (ACM), which refers to a ridge and a groove pattern that can be induced on the epithelial surface and to an identical pattern seen deeper in the epithelium by retroillumination.[15] Further progress has been accomplished with new technologies reconstructing SNP images from three-dimensional image stacks and generating an extended field of view by mosaicking these SNP images.[15–17]
Peripheral nerve dysfunction may develop in patients with recently diagnosed diabetes[18,19] and even earlier in individuals with prediabetes.[20,21] Whether CCM and skin biopsy may detect nerve pathology shortly after diagnosis of type 2 diabetes (T2D) and to what extent it correlates with measures of peripheral nerve function and structure is currently unknown. Therefore, the aim of this study was to evaluate the role of CCM compared with IENFD and quantitative small nerve fiber and large nerve fiber function tests in detecting early nerve damage in patients with recently diagnosed T2D.
Diabetes. 2014;63(7):2454-2463. © 2014 American Diabetes Association, Inc.
