Corneal Confocal Mircoscopy in Impaired Glucose Tolerance
A recent study has shown a significant reduction in IENFD and abnormal corneal nerve morphology in patients with type 2 diabetes of short duration, suggesting that neuropathy may be an early complication, and of course, longitudinal data from the Rochester cohort suggest that duration and severity of exposure to hyperglycemia are related to the severity of neuropathy. In the current study, we show a significant increase in neuropathic symptoms, consistent with the MONICA/KORA Augsburg Surveys, which also found a threefold increase in neuropathic pain in subjects with IGT. We also show a significant alteration in sudomotor function, whereas cardiac autonomic function and electrophysiology were normal, similar to a previous study in subjects with IGT demonstrating an abnormal sympathetic skin response but normal results on electrophysiology and standard autonomic function tests. These latter findings are similar to a large population-based study that also showed no electrodiagnostic abnormalities in subjects with impaired fasting glucose or IGT. However, we demonstrate a significant abnormality in VPT, WT, and CT, similar to the San Luis Valley study, which also reported impaired VPT in 11.2% of subjects with IGT compared with 3.5% in control subjects.
Previous studies have demonstrated a reduction in IENFD in subjects with IGT, which improved after lifestyle intervention, suggesting that this early abnormality may be amenable to treatment. We now confirm a significant reduction in IENFD in subjects with IGT. In addition, we also demonstrate a significant abnormality in corneal nerve morphology using the noninvasive technique of CCM and indeed show that 40.5% of subjects with IGT have significant small-fiber damage based on CNFD reduction. CCM provides a unique opportunity to noninvasively and rapidly assess unmyelinated C fibers in vivo, which has important diagnostic and prognostic implications. In conclusion, this study shows evidence of neuropathy in subjects with IGT, as evidenced by abnormal symptoms, signs, quantitative sensory testing, skin biopsy, and CCM, but not neurophysiology.
Conclusions
A recent study has shown a significant reduction in IENFD and abnormal corneal nerve morphology in patients with type 2 diabetes of short duration, suggesting that neuropathy may be an early complication, and of course, longitudinal data from the Rochester cohort suggest that duration and severity of exposure to hyperglycemia are related to the severity of neuropathy. In the current study, we show a significant increase in neuropathic symptoms, consistent with the MONICA/KORA Augsburg Surveys, which also found a threefold increase in neuropathic pain in subjects with IGT. We also show a significant alteration in sudomotor function, whereas cardiac autonomic function and electrophysiology were normal, similar to a previous study in subjects with IGT demonstrating an abnormal sympathetic skin response but normal results on electrophysiology and standard autonomic function tests. These latter findings are similar to a large population-based study that also showed no electrodiagnostic abnormalities in subjects with impaired fasting glucose or IGT. However, we demonstrate a significant abnormality in VPT, WT, and CT, similar to the San Luis Valley study, which also reported impaired VPT in 11.2% of subjects with IGT compared with 3.5% in control subjects.
Previous studies have demonstrated a reduction in IENFD in subjects with IGT, which improved after lifestyle intervention, suggesting that this early abnormality may be amenable to treatment. We now confirm a significant reduction in IENFD in subjects with IGT. In addition, we also demonstrate a significant abnormality in corneal nerve morphology using the noninvasive technique of CCM and indeed show that 40.5% of subjects with IGT have significant small-fiber damage based on CNFD reduction. CCM provides a unique opportunity to noninvasively and rapidly assess unmyelinated C fibers in vivo, which has important diagnostic and prognostic implications. In conclusion, this study shows evidence of neuropathy in subjects with IGT, as evidenced by abnormal symptoms, signs, quantitative sensory testing, skin biopsy, and CCM, but not neurophysiology.