Biopsy specimens of the sural nerve obtained from 28 middle-aged and elderly diabetics suffering from neuropathy were studied morphometrically. Myelinated nerve fiber density, especially large fibers, was decreased, and the bimodal distribution of myelinated fiber diameter shifted to unimodal distribution containing only a small fiber peak and the mean diameter of myelinated fiber was decreased. An insulin-treated group and a group with severe retinopathy showed a prominent decrease of myelinated fiber density; the severity and duration of diabetes may be a factor in this decrease. Large unmyelinated nerve fibers were also decreased and the mean diameter of unmyelinated fibers was reduced. Three patients with prominent autonomic nervous system symptoms showed a significant reduction of total unmyelinated fibers. The linear correlation between the square root of the transverse axis cylinder area and the number of myelin lamellae was obscured, and the plots were towards two directions, axonal atrophy and remyelination in diabetes. The latter process tended to be dominant in the middle-aged patients, but the importance of these two processes was reversed with age. To discuss the morphological changes of the sural nerve in diabetic neuropathy, the influence of aging as well as the duration, severity and clinical symptoms should be considered.
