Morphological changes of the peripheral nerves evaluated by high‐resolution ultrasonography are associated with the severity of diabetic neuropathy, but not corneal nerve fiber pathology in patients with type 2 diabetes

Aims/Introduction To evaluate the morphological changes of the median and posterior tibial nerve using high‐resolution ultrasonography, and the corneal C fiber pathology by corneal confocal microscopy in type 2 diabetic patients. Materials and Methods The cross‐sectional area, hypoechoic area and maximum thickness of the nerve fascicle of both nerves were measured by high‐resolution ultrasonography in 200 type 2 diabetic patients, stratified by the severity of diabetic neuropathy, and in 40 age‐ and sex‐matched controls. These parameters were associated with corneal C fiber pathology visualized by corneal confocal microscopy, neurophysiological tests and severity of diabetic neuropathy. Results The cross‐sectional area, hypoechoic area and maximum thickness of the nerve fascicle of both nerves in patients without diabetic neuropathy were larger than those in control subjects ( P  < 0.05 to P  < 0.001), and further increased relative to the severity of neuropathy ( P  < 0.0001). All morphological changes of both nerves were negatively associated with motor and sensory nerve conduction velocity ( P  = 0.01 to P  < 0.0001), and directly associated with 2,000‐Hz current perception threshold ( P  = 0.009 to P  < 0.001). The significant corneal C fiber pathology occurred before developing the neuropathy, and deteriorated only in patients with the most severe neuropathy. The association between the morphological changes of both nerves and corneal C fiber pathology was poor. Conclusions The morphological changes in peripheral nerves of type 2 diabetic patients were found before the onset of neuropathy, and were closely correlated with the severity of diabetic neuropathy, but not with corneal C fiber pathology.