Objective: Small-fiber neuropathies may be symptomatic yet escape detection by standard tests. We hypothesized that morphologic changes in intraepidermal nerves would correlate with clinical measures of small-fiber neuropathy.
Research design and methods: We studied 25 diabetic and 23 nondiabetic patients with neuropathy defined by signs, symptoms, and quantitative testing and 20 control subjects. Skin biopsies were obtained from forearm, thigh, proximal leg, and distal leg, and nerves identified using immunofluorescence with antibody to protein gene product (PGP) 9.5.
Results: Mean dendritic length (MDL) (P < 0.01) and intraepidermal nerve fiber density (IENF) (P < 0.001) progressively decreased from proximal to distal sites only in patients with neuropathy. There was a significant reduction in IENF when comparing control subjects and patient groups in the distal leg (P < 0.001). MDL was significantly decreased in the thigh (P < 0.005) and in the proximal (P < 0.01) and distal (P < 0.002) leg in patients compared with control subjects. IENF was not significantly altered in diabetic patients of <5 years' duration, but significantly decreased in patients with >5 years' duration. MDL showed a linear decrease with increasing duration of diabetes. Distal leg IENF showed significant negative correlations with warm (P < 0.02) and cold (P < 0.05) thermal threshold, heat pain (P < 0.05), pressure sense (P < 0.05), and neurological disability score total sensory (P < 0.03) and total neuropathy (P < 0.03) values.
Conclusions: IENF was not significantly altered in these patients at <5 years' duration of diabetes, but fell significantly after 5 years of diabetes. MDL exhibited a linear loss with time, suggesting a different mechanism of change. MDL and IENF together may prove a useful end point in therapeutic trials for neuropathy.