Correlation between skin biopsy with quantification of intraepidermal nerve fiber and the severity of sciatic nerve traction injury in rats

BACKGROUND: To predict the severity of nerve traction injury by skin biopsy with quantification of intraepidermal nerve fibers density (IENFD). METHODS: Traction injuries to the right sciatic nerve of Sprague-Dawley rats with the use of different weights (0, 25, 50, 100, 200, 400, and 600 g) were performed. Sham operations were performed on the left sciatic nerve. After a period of 7 days, IENFD derived from quantification of protein gene product 9.5-immunoreactive intraepidermal nerve fibers of the hindpaw skin were calculated to compare with numbers of intact teased fibers of tibia nerve. RESULTS: There were 100% ± 0%, 94% ± 5%, 52% ± 8%, 48% ± 6%, 42% ± 7%, 9% ± 3%, and 0% ± 0% of teased nerve fibers remained intact after traction injury with 0 g, 25 g, 50 g, 100 g, 200 g, 400 g, and 600 g weights, respectively. When compared with IENFD of the control rats (ipsilateral paw: 21.6 ± 0.6; contralateral paw: 20.1 ± 0.8 fibers/mm), there were loss of nearly half of the small fibers after 50 g, 100 g, and 200 g weight traction injury in ipsilateral paw (10.1 ± 1.2, 7.4 ± 1.5, and 8.3 ± 2.2 fibers/mm, respectively) and contralateral paw (11.4 ± 0.9, 9.6 ± 0.6, and 10.0 ± 1.5 fibers/mm, respectively). After 400 g and 600 g weight traction injury, there was severe (0.2 ± 0.2 fibers/mm) to complete destruction of the small fibers in ipsilateral paw and marked reduction in contralateral paw (5.5 ± 0.7 and 4.3 ± 0.7 fibers/mm, respectively). CONCLUSIONS: With the ability to classify the nerve traction injury into a mild, moderate, or severe injury, correlations can be made between skin biopsy with IENFD and the severity of nerve traction injury. However, the extent of nerve injury cannot be differentiated within group of moderate injury with the use of three different traction weights.